Thyroid hormone receptor β-specific agonist GC-1 increases energy expenditure and prevents fat-mass accumulation in rats

in Journal of Endocrinology

It is well known that thyroid hormone affects body composition; however, the effect of the thyroid hormone receptor β (TRβ)-selective thyromimetic GC-1 on this biological feature had not been demonstrated. In the current study, we compared the effects of a 6-week treatment with triiodothyronine (T3; daily injections of 3 or 6 μg/100 g body weight) or GC-1 (equimolar doses) on different metabolic parameters in adult female rats. Whereas all animals gained weight (17–25 g) in a way not basically affected by T3 or GC-1 treatment, only T3 treatment selectively increased food intake (50–70%). Oxygen consumption was significantly and equally increased (50–70%) by T3 and GC-1. Analysis of body composition by dual-energy X-ray absorptiometry (DEXA) revealed that, whereas control animals gained about 80% of fat mass, T3- or GC-1-treated animals lost 70–90 and ~20% respectively. Direct analysis of the carcass showed that T3 treatment promoted a 14–74% decrease in fat content but GC-1 treatment promoted only a 15–23% reduction. The gain in lean mass by DEXA and the carcass protein content were not affected by T3 or GC-1 treatment. However, the mass of individual skeletal muscles was negatively affected by T3 but only barely by GC-1. These findings highlight the potential use of GC-1 for the treatment of obesity and the metabolic syndrome.

Abstract

It is well known that thyroid hormone affects body composition; however, the effect of the thyroid hormone receptor β (TRβ)-selective thyromimetic GC-1 on this biological feature had not been demonstrated. In the current study, we compared the effects of a 6-week treatment with triiodothyronine (T3; daily injections of 3 or 6 μg/100 g body weight) or GC-1 (equimolar doses) on different metabolic parameters in adult female rats. Whereas all animals gained weight (17–25 g) in a way not basically affected by T3 or GC-1 treatment, only T3 treatment selectively increased food intake (50–70%). Oxygen consumption was significantly and equally increased (50–70%) by T3 and GC-1. Analysis of body composition by dual-energy X-ray absorptiometry (DEXA) revealed that, whereas control animals gained about 80% of fat mass, T3- or GC-1-treated animals lost 70–90 and ~20% respectively. Direct analysis of the carcass showed that T3 treatment promoted a 14–74% decrease in fat content but GC-1 treatment promoted only a 15–23% reduction. The gain in lean mass by DEXA and the carcass protein content were not affected by T3 or GC-1 treatment. However, the mass of individual skeletal muscles was negatively affected by T3 but only barely by GC-1. These findings highlight the potential use of GC-1 for the treatment of obesity and the metabolic syndrome.

Keywords:

Introduction

Thyroid hormone controls gene expression by interacting with nuclear receptors (TRs), which are hormone-inducible transcriptional factors (Lazar 1993). Two genes encode TRs, TRα and TRβ (Freedman 1992). At least two isoforms of TRα and TRβ have been identified and are the result of alternative splicing. TRα1, TRβ1 and TRβ2 isoforms bind T3, while TRα2 does not and functions, at least in vitro, as a TRα1 and TRβ1 antagonist (Katz & Lazar 1993). Activation of TRs causes a multitude of physiological effects that range from actions on the embryonic development to actions on the maintenance of energy homeostasis in adults (Motomura & Brent 1998).

It is fascinating that an excess of thyroid hormone can result in some therapeutically desirable effects, such as increased metabolic rate, lipolysis, cholesterol lowering, improvement of heart contractility and thyroid-stimulating hormone (TSH) suppression, which is beneficial in patients with thyroid cancer (Motomura & Brent 1998). At the same time, systemic thyrotoxicosis also results in undesirable effects, including tachycardia, arrhythmia, muscle wasting, nervousness, fatigue and loss of bone mass (Motomura & Brent 1998). A series of studies in mice with inactivation or mutation of different TR isoforms (Fowler et al. 1996, Fraichard et al. 1997, Johansson et al. 1998, Wikstrom et al. 1998, Gothe et al. 1999, Gauthier et al. 2001, Flamant et al. 2002), as well as studies in patients with the syndrome of resistance to thyroid hormone (characterised by mutations in TRβ; Refetoff 2003, Cheng 2005), suggests that TR isoforms selectively mediate tissue-specific thyroid hormone responses. It is a general consensus that TRα mediates the effects of thyroid hormone on the heart, while TRβ mediates its effects on plasma cholesterol and TSH secretion, some of the desirable effects of systemic thyrotoxicosis (Baxter et al. 2004). Therefore, the development of T3 analogues with preferred TRβ binding action could be a possible strategy of achieving desirable effects of T3 and bypassing the undesirable effects.

GC-1 is a synthetic analogue of thyroid hormone that is relatively selective for both binding and activation functions of TRβ1 over TRα1 (Chiellini et al. 1998). GC-1 has several structural differences with respect to the natural hormone T3, including replacement of the three iodine residues with methyl and isopropyl groups, of the biaryl ether linkage with a methylene linkage and of the amino acid side chain with an oxyacetic acid side chain (Chiellini et al. 1998). GC-1 binds TRβ1 with the same affinity as it does T3 but binds TRα1 with an affinity about ten times lower than that for T3. It is interesting that GC-1 presents selective actions in vitro (Chiellini et al. 1998) and in vivo (Trost et al. 2000, Ribeiro et al. 2001). The differential effects of GC-1 vs T3 on the thermogenesis by brown adipose tissue (Ribeiro et al. 2001), tadpole metamorphosis (Furlow et al. 2004) and the development of the bone and central nervous system (Morte et al. 2002, 2004, Manzano et al. 2003, Freitas et al. 2005) may be the result of GC-1 selectivity for TRβ. On the other hand, the selective effects of GC-1 may also be related to the body distribution of TR isoforms. In agreement with studies in which the TRβ gene has been disrupted (Johansson et al. 1999), GC-1 has almost no effects on the heart, which expresses mainly TRα1, but lowers serum levels of cholesterol and triglycerides, in agreement with a predominant expression of TRβ1 in the liver (Trost et al. 2000). Other studies also suggest that the selective actions of GC-1 might also be explained by differential tissue uptake since it presents clear tissue-specific accumulation (Trost et al. 2000, Baxter et al. 2004). It has been shown, for example, that GC-1 accumulates selectively in the liver as compared with the heart. The tissue/plasma ratio was similar for GC-1 and T3 in the liver but was 30 times lower in the heart (Trost et al. 2000).

It is well known that thyrotoxicosis affects body composition, reducing fat mass and lean mass (Lonn et al. 1998, Riis et al. 2005). In primates, treatment with GC-1 has been shown to increase oxygen consumption and to reduce body weight (Grover et al. 2004), but effects on body composition had not been determined yet. Here, we show that treatment with GC-1 increased the metabolic rate, had no effect on food intake and decreased fat mass while sparing the lean mass of rats. These data illustrate the potential of GC-1 as an agent for the treatment of metabolic disorders, including obesity.

Materials and Methods

Animals and drugs

All experimental procedures were performed in accordance with the guidelines of the Standing Committee on Animal Research of the University of Sao Paulo. Female Wistar rats were obtained from our breeding colony and maintained under controlled conditions of light and temperature (12 h darkness:12 h light cycle at 25 °C). All animals were kept in plastic cages, four per cage, and had free access to food (rat chow containing 1.4% Pi, 0.7% Ca and 4.5 IU/g vitamin D) and water. At the age of 100 days and a weight of 210–220 g, the animals were randomly divided into five groups (n = 8 per group): (i) control, treated with saline; (ii) 10×T3, treated with 3 μg T3/100 g body weight (BW) per day, which is equivalent to ten times the physiological dose of T3 (Bianco & Silva 1987); (iii) 20×T3, treated with double of the previous T3 dosage (6 μg T3/100 g body weight (BW) per day); (iv) 10xGC-1, treated with 1.5 μg GC-1/100 g BW per day and (v) 20xGC-1, treated with 3 μg GC-1/100 g BW per day. The latter two groups were treated with GC-1 in equimolar doses of 10×T3 and 20×T3 respectively. The equimolar doses of GC-1 were calculated from the molecular mass of T3 (mol mass = 651) and GC-1 (mol mass = 328.4). T3 (Sigma Chemicals) was dissolved in 40 mM NaOH, and GC-1 was dissolved in dimethyl sulfoxide (DMSO) to a concentration of 1 mg/ml; either T3 or GC-1 were then diluted in saline and administered i.p. every day for 6 weeks. BW was measured thrice a week (on Mondays, Wednesdays and Fridays). Body length (nose to base of the tail) was determined at the end of the experimental period.

Serum parameters

At the end of the experimental period, the animals were killed by decapitation and the blood of the trunk was collected. The serum was separated by centrifugation and immediately frozen. Total thyroxine (T4) and T3 serum levels were measured by commercial RIA kits (RIA-gnost T4 and RIA-gnost T3, CIS Bio international, France). For the T4 and T3 assays, standard curves were constructed in our laboratory with a pool of charcoal-stripped rat serum. To determine whether GC-1 could cross-react in the T4 and T3 RIAs, we measured serum levels of T4 and T3 in hypothyroid rats treated with different doses of GC-1. Serum T4 was undetectable in all animals, and no differences were seen in serum levels of T3 between the GC-1-treated animals and the hypothyroid-untreated animals, indicating that T4 and T3 RIAs cannot detect GC-1.

Food intake

Once a week (weeks 1–6), the animals were individually maintained in metabolic cages for 24 h for determination of food intake. The rat chow (60–70 g) was weighed before (initial weight) and after (final weight) placing the animals in the metabolic cages for 24 h. Food intake was calculated by the difference between the final and initial weight of the chow (food intake = initial weight–final weight). A basal measurement was done 1 week before the initiation of T3 or GC-1 treatment (week 0).

Determination of body composition by dual-energy X-ray absorptiometry (DEXA)

Lean mass (LM) and fat mass (FM) were measured by dual-energy X-ray absorptiometry (DEXA) using the pDEXA Sabre Bone Densitometer and the pDEXA Sabre Software version 3.9.4 (Norland Medical Systems, Fort Atkinson, WI, USA), both specially designed for small animals. The research mode scan option was used for the measurements. Pixel spacing for the scan was set to 0.5×1.0 mm; the scan width to 10.5 cm; the scan length to 11.5 cm and the scan speed to 8 mm/s. Since the scan window of the bone densitometer was not large enough to allow a total body scan of the rats used in this study, the scans were performed from the first lumbar vertebra to the hind limbs. This region was named hind body (HB) in the present study. For the scans, the animals were anaesthetised with a cocktail of ketamine and xylazine (30 and 10 mg/kg BW i.p. respectively) and scanned in the prone position. The animals were scanned before (basal scan) and after (final scan) 6 weeks of treatment. ΔLM and ΔFM were calculated, for each animal, by the difference between both scans (final scan–basal scan). For the scan analysis, the bone mineral density (BMD) histogram averaging width (BHAW) was set to 0.01 g/cm2 for all scans. This parameter can be considered as a variable window that ‘refines’ the distribution of the scan data and allows the definition of the threshold for bone and soft tissues (LM and FM). To establish the appropriated BHAW to this study, we analysed scans of six rats. Two regions of interest (ROIs) were used: HB and soft tissue (ST), a ROI of 1 cm2 that included exclusively soft tissue. This ROI was placed 0.5 cm to the rear of the left femur and 0.5 cm to the left of the pelvis. BMD, LM and FM of HB and ST were measured using various BHAWs, ranging from 0.005 to 0.2 g/cm2. The values for each parameter were plotted and analysed. BMD and LM values increased and FM values decreased from the BHAW of 0.005–0.01 g/cm2. From the BHAW of 0.01–0.2 g/cm2, a plateau was established for each parameter. Thus, 0.01 g/cm2 was the BHAW of choice since it determined the first point in the plateau and allowed the greatest discrimination among BMD, FM and LM for all scans. The precision in vivo was evaluated by calculating the coefficient of variation (CV = 100× s.d./mean) of six repeated measurements of a 2-month-old female rat weighing 207 g. The animal was repositioned after each scan. The CV of LM and FM of the HB were 1.7 and 1.9% respectively. The precision in vitro was also expressed as CV and calculated by measuring the BMD of a phantom, with a nominal density of 0.929 g/cm2. This CV was 0.8% throughout the experiment. The performance of the system was assessed and maintained by the quality assurance test (QA test), which includes scanner calibration and phantom scanning. The QA test was carried out on each day that scans were to be performed.

Body composition by carcass analysis

Carcasses were thawed overnight at 4 °C, reweighed, cut in small pieces and then thoroughly homogenised with distilled water (the volume of water equals double the weight of the carcasses) in a blender (Kinematica AG., Lucerne, Switzerland). Aliquots of homogenate were used for measurement of water, protein and fat content. The water content was determined according to the method of Bertin et al.(1998). Briefly, two aliquots of homogenate per animal were weighed before and after drying for 18 h in an oven at 103 °C. Fat content was determined from triplicate aliquots of homogenate per animal according to Folch et al.(1957). Briefly, lipid was extracted from 0.3 g aliquots of homogenate with a 2:1 chloroform:methanol solution. The lipid-containing chloroform layer was separated and dried to a constant weight. The protein content was determined by the biuret method, as described by Brooks et al.(1995).

Weight of fat pads, skeletal muscles and heart

Immediately after animals were killed, the retroperitoneal fat pad, the heart and the quadriceps, gastrocnemius, soleus and extensor digitorum longus (EDL) were carefully dissected out and weighed (wet weight). The samples of the skeletal muscles were then transferred to an incubator at 60 °C for 48 h and weighed again (dry weight). The water content of each sample was determined by the difference between the wet and dry weights (water content = wet weight–dry weight). All weights were expressed in mg/g BW.

Oxygen consumption

Resting oxygen consumption (VO2) was measured in conscious rats in an open-circuit respirometer system (S-3A/1, Ametek, Pittsburgh, PA, USA) as previously described (Withers 1977) at the end of the experimental period. All measurements were carried out at room temperature (>25 °C) over a period of 1 h during the morning (0900–1200 h). Animals were studied while they were in the fed condition and were maintained under normal experimental conditions until immediately before the measurements were taken. Online data were collected and analysed with a computer system running on DataCan V software (Sable Systems, Salt Lake City, UT, USA). Results were corrected for environmental temperature and atmospheric pressure and expressed in terms of microlitres of O2 per min/g BW.

Statistical analysis

One-way ANOVA was used to compare more than two groups and was always followed by the Student–Newman–Keuls test to detect differences between groups. For all tests, P < 0.05 was considered statistically significant. All results are expressed as the mean ± s.e.m. For statistical analysis, we used the GraphPad Instat Software (GraphPad Software, San Diego, CA, USA).

Results

Serum levels of T3 and T4

As expected, serum levels of T3 were significantly higher in the 10×T3- and 20×T3-treated groups than in the controls (Table 1). Serum levels of T3 were not affected by treatment with GC-1. On the other hand, serum levels of T4 were lower in the 10×T3-, 20×T3- and 20×GC-1-treated animals than in the controls.

Effects of T3 and GC-1 on body weight and food intake

Body weight was barely affected by T3 and was not affected by GC-1 (Fig. 1A and B). Both 10×T3 and 20×T3 treatments reduced body weight by approximately 6 and 10% when compared with controls (P < 0.05 for both) respectively, from day 6 to day 10 of treatment. Rats treated with 20×T3 also presented with a lower body weight than control rats (−7.4%, P < 0.05) from day 24 to day 27 of treatment, but by the end of the treatment period, all animals were the same body weight. The body length was not affected by T3 or GC-1.

Treatments with 10×T3 and 20×T3 increased food intake by 50 and 72% (P < 0.001 for both vs controls) respectively, in week 2 of treatment, while treatment with GC-1 had no effect on food intake (Fig. 1C). Food intake in the T3-treated animals remained ≈63% greater than that in controls until the end of the treatment period.

Effects of T3 and GC-1 on oxygen consumption

At the end of the experimental period, resting oxygen consumption (VO2) was significantly and equally increased by treatment with T3 or GC-1 by about 46–88% when compared with that of controls (Fig. 2).

Effects of T3 and GC-1 on fat mass and fat content

Analysis of body composition by DEXA showed that treatment with T3 or GC-1 negatively affected ΔFM (Fig. 3A). While control rats presented an increase of approximately 83% (6.5 g) in fat mass, 10×T3- and 20×T3-treated rats lost approximately 74% (4.2 g) and 91% (5.9 g) respectively, of their fat mass. Treatment with 10×GC-1 resulted in a gain of fat mass of only 21% (1.7 g), and treatment with 20×GC-1 induced a decrease in fat mass of 20% (1.3 g).

The determination of fat content by analysis of the carcass showed that 10×T3, 20×T3, 10×GC-1 and 20×GC-1 significantly reduced the fat content by 14, 74, 15 and 23% respectively, when compared with controls (Fig. 3B). Treatment with 10×T3, 20×T3 and 20×GC-1 significantly reduced the mass of the retroperitoneal fat pad by 68, 73 and 48% respectively (Fig. 3C).

Effects of T3 and GC-1 on lean mass, protein content, skeletal muscle mass and heart mass

Treatment with T3 or GC-1 did not affect ΔLM, as determined by DEXA, and the protein content, as determined by carcass analysis. Nevertheless, skeletal muscle mass was negatively affected by T3 (Table 2). The wet and dry masses of the quadriceps, gastrocnemius and soleus of the T3-treated animals were significantly lower (13–36%) than those of the control animals, while these parameters were not affected in the EDL muscle. Treatment with 20×GC-1 significantly reduced wet and dry masses of the quadriceps by 16 and 24% respectively. None of the other skeletal muscles were affected by GC-1. The wet mass of the quadriceps increased 15% (P < 0.01 vs control) after treatment with 10× GC-1, which can be explained by an increase in its water content (19% vs control, P < 0.001). As expected, treatment with 10×T3 or 20×T3 resulted in cardiac hypertrophy, characterised by an increase in the dry mass of the heart (33 and 46% vs control respectively), while GC-1 treatment had no effect.

Discussion

The present study shows that treatment with GC-1 increases VO2 (Fig. 2), a finding corroborated by a previous report (Grover et al. 2004). It is interesting however that 10×GC-1 and 20×GC-1 increased VO2 by 53 and 90% respectively, whereas Grover et al.(2004) observed only modest (5–10%) increases in VO2 with doses of GC-1 in this range. Such a discrepancy might be explained by the much longer duration of GC-1 treatment in the current investigation (1 vs 6 weeks).

In addition, other differences between these studies may have accounted for some of the variation in oxygen consumption, such as gender (male vs female), strain of rats (Sprague–Dawley vs Wistar), the route of ligand administration (gavage vs i.p. injection) and diet (cholesterol-fed rats vs regular-fed rats). An important and original finding of the present investigation was that the GC-1-induced increase in VO2 was not accompanied by an increase in food intake (Fig. 1C) but led to a 20% reduction in body fat content (Fig. 3A–C) without substantially affecting lean or skeletal muscle mass (Table 2).

It is well known that thyroid hormone promotes lipolysis (Wahrenberg et al. 1994). In the present study, DEXA analysis showed that animals treated with 10×T3 and 20×T3 presented with a decrease in fat mass of approximately 74 and 91%, while control animals gained fat mass (Fig. 3A). This finding is in agreement with the data from carcass analysis of body composition. The treatments with 10×T3 and 20×T3 reduced the fat content of the animals by 14 and 74% respectively (Fig. 3B). It is noteworthy that GC-1 also decreased the fat mass. The animals treated with 10×GC-1 gained significantly less fat mass than did controls, and rats treated with 20×GC-1 lost approximately 20% of their fat mass (Fig. 3A). The carcass analysis showed that 10×GC-1 and 20××GC-1 reduced the fat content by 15 and 23% respectively, when compared with control animals (Fig. 3B), an effect that was less pronounced than that of T3. This could be explained by a lower uptake of GC-1 by the adipose tissue when compared with the uptake of T3 (Trost et al. 2000). In view of the recognised stimulatory effect of thyroid hormone on lipolysis (Moller et al. 1996), it is predictable that the reducing effect of GC-1 on fat mass shown in the present study was a consequence of an increase in lipolysis and not of a reduction in lipogenesis. Indeed, Ribeiro et al.(2001) showed that equimolar doses of T3 or GC-1 equally increased the mRNA expression of malic enzyme, an important NADPH-generating lipogenic enzyme, in the livers of mice, suggesting that GC-1, like T3, increases lipogenesis.

It is known that thyroid status strongly influences the contractile function and the mass of the skeletal muscle. However, by DEXA, we could not detect alterations in lean mass induced by T3 or GC-1. These results could be explained by a limited sensitivity of this method of body composition analysis in small animals. In addition, it is important to consider that lean mass by DEXA is determined by the content of minerals that are not from bone, proteins, water and glycogen. As a consequence, changes in these body components, or even the absence of alterations, may mask small or moderate changes in the skeletal muscle mass. In fact, in the present study, the effects of T3 excess on the skeletal muscle were compatible with those described in the literature (White et al. 2001). We showed that the quadriceps, gastrocnemius and soleus of animals treated with T3 present lower mass than do those of the control group (Table 2). The EDL mass however was not affected by T3 excess. This corroborates a series of studies that showed that this muscle is weakly responsive to the thyroid status in relation to protein metabolism (Angeras & Hasselgren 1985), muscular function (Nicol & Bruce 1981), the expression of genes related to their function (dos Santos et al. 2001) and histological modifications (Devor & White 1995, dos Santos et al. 2001). In the present study, we showed that the mass of all skeletal muscles, except for the quadriceps, was not decreased by GC-1 (Table 2). It is interesting that GC-24, a TRβ-selective compound similar to GC-1, mostly spares skeletal muscle from changes in fibre type and tropism induced by T3 (Miyabara et al. 2005). The predominance of TRα over TRβ (White et al. 2001) and/or the poorer penetration of GC-1 in the skeletal muscle (Trost et al. 2000), compared with T3, may explain in part the minimal effects of these TRβ-selective compounds on this tissue.

In addition to evaluating the effect of T3 or GC-1 on skeletal muscle, we evaluated the effect of these agents on cardiac muscle mass. This analysis was done to obtain positive and negative controls for the treatment with T3 or GC-1 respectively. It is well known that an excess in thyroid hormone causes cardiac hypertrophy (Danzi & Klein 2004) and that GC-1 does not modify the cardiac mass and function (Trost et al. 2000). As expected, T3, but not GC-1, increased the heart mass (Table 2), which is a good positive control for the ability of the doses of T3 used in the present study to promote thyrotoxicosis.

We also found that body weight was barely affected by T3 treatment and, different from what has been shown in primates (Grover et al. 2004), body weight was not affected by GC-1. T3-treated animals presented a body weight that was lower than that of controls only from day 6 to day 9 and from day 24 to day 27 of treatment (Fig. 1A and B). The absence or minimal effects of T3 on body weight of rats were noticed previously (Yu et al. 1998, Soukup et al. 2001). In the present study, it can be explained by the increase in food intake induced by T3 (Fig. 1C). On the other hand, GC-1 had no effect on energy ingestion, despite an increase in oxygen consumption at the same magnitude as that with T3 (Fig. 2). The increase in food intake is characteristic of hyperthyroidism. It is believed that one of the mechanisms by which T3 increases food intake involves the progressive depletion of fat stocks, a signal known to regulate the ingestion of energy (Iossa et al. 2001). However, T3 was recently shown also to stimulate food intake directly, through the hypothalamic ventromedial nucleus and independently of modifications in energy consumption (Kong et al. 2004). Considering the selectivity of GC-1 for TRβ and that this T3 analogue increased oxygen consumption, reduced the body fat content, but did not affect food intake, our data suggest that the direct effect of T3 on energy ingestion is essential and likely to be mediated by TRαin rats. Another point to be considered is the lack of effect of GC-1 on body weight (Fig. 1B), which is unusual with regard to energy balance since it increased VO2 without increasing energy ingestion. The unchanged body weight is possibly explained by the fact that GC-1 significantly reduced body fat content and barely affected muscle mass.

As pointed out before, the TRβ selectivity of GC-1 may partially explain some effects of GC-1 observed in the present investigation. If this assumption is true, we could consider that TRβ mediates T3 actions that decrease fat mass and increase VO2, whereas TRα mediates T3 actions that decrease muscle mass and increase food intake. However, GC-1 presents other properties that must be considered and that may contribute to its selective effects. The selective tissue uptake of GC-1 is an important point, as mentioned before; there is a lower uptake of GC-1 by the skeletal muscle and adipose tissue than of T3 (Trost et al. 2000). In addition, a recent in vitro study showed that GC-1 behaves largely as a T3 agonist but recruits coactivators or corepressors on some thyroid hormone response elements differently and does this independently of the TR isoform (Gloss et al. 2005). The functional consequence of these observations would be a differential regulation of some genes by GC-1 vs T3 that is independent of the GC-1 selectivity for TRβ. It seems therefore that the mechanisms underlying the differential effects of GC-1 vs T3 on the biological systems, including body composition, depend on a series of different properties of these ligands, besides the TRβ selectivity of GC-1, which remains to be further investigated.

In conclusion, this is the first study showing that treatment with GC-1 decreases the body content of adipose tissue while it does not increase food intake and barely affects the mass of skeletal muscle. The reduction of body fat content added to other GC-1 effects previously described, such as reduction of serum levels of cholesterol, triglycerides and TSH (Trost et al. 2000, Freitas et al. 2003, Grover et al. 2004), and the lack of deleterious effects of GC-1 on the heart structure and function (Trost et al. 2000), skeletal muscle mass and bone mass (Freitas et al. 2003) suggest that GC-1 has the potential to be used as a therapeutic agent for a variety of disorders, such as obesity, hyperlipidaemia and hypercholesterolaemia.

Table 1

Serum levels (ng/ml) of T3 and T4. Values are the means ± s.e.m. (n = 8 for all groups)

T3T4
Significance among groups was determined by ANOVA followed by Student–Newman–Keuls test. *P < 0.001 vs control.
Group
Control1.02 ± 0.248.0 ± 2.7
10×T3>230.2 ± 1.2*
20×T3>231.9 ± 3*
10×GC-10.80 ± 0.0746.7 ± 1.3
20×GC-10.84 ± 0.0932.9 ± 2.9*
Table 2

Effects of T3 and GC-1 on skeletal mass and heart mass

Control10×T320×T310×GC-120×GC-1
Wet mass and dry mass are expressed as mg/g BW and H2O content as μl/g BW. Values are the mean ± s.e.m. (n = 8 for all groups). Significance among groups was determined by ANOVA followed by Student–Newman–Keuls test. *P < 0.01 vs control. P < 0.05 vs control. P < 0.001 vs control.
Muscle
Quadriceps
    Wet mass7.97 ± 0.286.38 ± 0.336.90 ± 0.16*9.19 ± 0.366.62 ± 0.28
    Dry mass2.27 ± 0.111.78 ± 0.101.96 ± 0.07*2.44 ± 0.141.73 ± 0.08
    H2O content5.69 ± 0.194.60 ± 0.234.94 ± 0.10*6.75 ± 0.244.90 ± 0.21*
Gastrocnemius
    Wet mass4.66 ± 0.143.00 ± 0.193.95 ± 0.284.71 ± 0.224.55 ± 0.15
    Dry mass1.31 ± 0.060.83 ± 0.0510.07 ± 0.0810.26 ± 0.091.21 ± 0.05
    H2O content3.35 ± 0.112.16 ± 0.132.88 ± 0.193.44 ± 0.153.34 ± 0.10
Soleus
    Wet mass1.14 ± 0.120.84 ± 0.04*0.85 ± 0.01*0.98 ± 0.051.10 ± 0.07
    Dry mass0.32 ± 0.030.24 ± 0.01*0.23 ± 0.004*0.27 ± 0.010.29 ± 0.01
    H2O content0.82 ± 0.080.60 ± 0.03*0.61 ± 0.01*0.71 ± 0.040.81 ± 0.05
EDL
    Wet mass0.37 ± 0.010.35 ± 0.010.35 ± 0.010.41 ± 0.010.40 ± 0.03
    Dry mass0.11 ± 0.0040.10 ±.0040.10 ± 0.0040.11 ± 0.010.11 ± 0.01
    H2O content0.27 ±.0.010.24 ±.0.010.25 ± 0.010.29 ± 0.0040.28 ± 0.01
Heart
    Wet mass3.48 ± 0.094.60 ± 0.095.34 ± 0.223.50 ± 0.093.43 ± 0.12
    Dry mass0.89 ± 0.051.18 ± 0.021.30 ± 0.050.85 ± 0.030.82 ± 0.03
    H2O content2.59 ± 0.083.42 ± 0.084.04 ± 0.172.65 ± 0.072.61 ± 0.10
Figure 1
Figure 1

Effects of T3 and GC-1 on body weight and food intake. (A) Body-weight response to treatment with T3. (B) Body-weight response to treatment with GC-1. Body weight was measured thrice a week in control rats and rats treated for 6 weeks with T3 or GC-1. (C) Food intake was determined weekly in control rats and rats treated for 6 weeks with T3 or GC-1. All values (A–C) are expressed as the mean ± s.e.m. (n = 8 per group). *P < 0.05 and P < 0.001, control vs 10×T3 and 20×T3 and P < 0.05, control vs 20×T3 by Student–Newman–Keuls test.

Citation: Journal of Endocrinology 193, 1; 10.1677/joe.1.07066

Figure 2
Figure 2

Effects of T3 and GC-1 on oxygen consumption. Resting oxygen consumption was measured at the end of the experimental period in control rats and rats treated for 6 weeks with T3 or GC-1. All values are expressed as the mean ± s.e.m. (n = 5 per group). *P < 0.01 and P < 0.001 vs control by Student–Newman–Keuls test.

Citation: Journal of Endocrinology 193, 1; 10.1677/joe.1.07066

Figure 3
Figure 3

Effects of T3 and GC-1 on change in fat mass, carcass fat content and retroperitoneal fat pad. All parameters were determined in control rats and rats treated for 6 weeks with T3 or GC-1. (A) ΔFat mass (final fat mass-basal fat mass) was determined in vivo by DEXA. (B) Carcass fat content. (C) Retroperitoneal fat pad. All values are expressed as the mean ± s.e.m. (n = 8 per group). *P < 0.05, P < 0.01 and P < 0.001 vs control by Student–Newman–Keuls test.

Citation: Journal of Endocrinology 193, 1; 10.1677/joe.1.07066

The authors are grateful to Dr Patrícia C Brum, from the Physical Education and Sports School, University of Sao Paulo, Brazil, for essential contributions in the VO2 measurements.

Funding
 This work was supported by a grant (process # 05/52910-4) from Fundação de Amparo à Pesquisa do Estado de São Paulo, Brazil (C H A Gouveia). The authors declare that there is no conflict of interest that would prejudice the impartiality of this scientific work.

References

  • AngerasU & Hasselgren PO 1985 Protein turnover in different types of skeletal muscle during experimental hyperthyroidism in rats. Acta Endocrinologica10990–95.

    • Search Google Scholar
    • Export Citation
  • BaxterJD Webb P Grover G & Scanlan TS 2004 Selective activation of thyroid hormone signaling pathways by GC-1: a new approach to controlling cholesterol and body weight. Trends in Endocrinology and Metabolism15154–157.

    • Search Google Scholar
    • Export Citation
  • BertinE Ruiz JC Mourot J Peiniau P & Portha B 1998 Evaluation of dual-energy X-ray absorptiometry for body-composition assessment in rats. Journal of Nutrition1281550–1554.

    • Search Google Scholar
    • Export Citation
  • BiancoAC & Silva JE 1987 Nuclear 353′-triiodothyronine (T3) in brown adipose tissue: receptor occupancy and sources of T3 as determined by in vivo techniques. Endocrinology12055–62.

    • Search Google Scholar
    • Export Citation
  • BrooksSP Lampi BJ Sarwar G & Botting HG 1995 A comparison of methods for determining total body protein. Analytical Biochemistry22626–30.

    • Search Google Scholar
    • Export Citation
  • ChengSY2005 Thyroid hormone receptor mutations and disease: beyond thyroid hormone resistance. Trends in Endocrinology and Metabolism16176–182.

    • Search Google Scholar
    • Export Citation
  • ChielliniG Apriletti JW Yoshihara HA Baxter JD Ribeiro RC & Scanlan TS 1998 A high-affinity subtype-selective agonist ligand for the thyroid hormone receptor. Chemistry and Biology5299–306.

    • Search Google Scholar
    • Export Citation
  • DanziS & Klein I 2004 Thyroid hormone and the cardiovascular system. Minerva Endocrinologica29139–150.

  • DevorST & White TP 1995 Myosin heavy chain phenotype in regenerating skeletal muscle is affected by thyroid hormone. Medicine and Science in Sports and Exercise27674–681.

    • Search Google Scholar
    • Export Citation
  • FlamantF Poguet AL Plateroti M Chassande O Gauthier K Streichenberger N Mansouri A & Samarut J 2002 Congenital hypothyroid Pax8(−/−) mutant mice can be rescued by inactivating the TR alpha gene. Molecular Endocrinology1624–32.

    • Search Google Scholar
    • Export Citation
  • FolchJ Lees M & Sloane Stanley GH 1957 A simple method for the isolation and purification of total lipids from animal tissues. Journal of Biological Chemistry226497–509.

    • Search Google Scholar
    • Export Citation
  • FowlerPB McIvor J Sykes L & Macrae KD 1996 The effect of long-term thyroxine on bone mineral density and serum cholesterol. Journal of the Royal College of Physicians of London30527–532.

    • Search Google Scholar
    • Export Citation
  • FraichardA Chassande O Plateroti M Roux JP Trouillas J Dehay C Legrand C Gauthier K Kedinger M Malaval L et al.1997 The T3R alpha gene encoding a thyroid hormone receptor is essential for post-natal development and thyroid hormone production. EMBO Journal164412–4420.

    • Search Google Scholar
    • Export Citation
  • FreedmanLP1992 Anatomy of the steroid receptor zinc finger region. Endocrine Reviews13129–145.

  • FreitasFR Moriscot AS Jorgetti V Soares AG Passarelli M Scanlan TS Brent GA Bianco AC & Gouveia CH 2003 Spared bone mass in rats treated with thyroid hormone receptor TRβ-selective compound GC-1. American Journal of Physiology. Endocrinology and Metabolism285E1135–E1141.

    • Search Google Scholar
    • Export Citation
  • FreitasFR Capelo LP O’Shea PJ Jorgetti V Moriscot AS Scanlan TS Williams GR Zorn TM & Gouveia CH 2005 The thyroid hormone receptor beta-specific agonist GC-1 selectively affects the bone development of hypothyroid rats. Journal of Bone and Mineral Research20294–304.

    • Search Google Scholar
    • Export Citation
  • FurlowJD Yang HY Hsu M Lim W Ermio DJ Chiellini G & Scanlan TS 2004 Induction of larval tissue resorption in Xenopus laevis tadpoles by the thyroid hormone receptor agonist GC-1. Journal of Biological Chemistry27926555–26562.

    • Search Google Scholar
    • Export Citation
  • GauthierK Plateroti M Harvey CB Williams GR Weiss RE Refetoff S Willott JF Sundin V Roux JP Malaval L et al.2001 Genetic analysis reveals different functions for the products of the thyroid hormone receptor alpha locus. Molecular and Cellular Biology214748–4760.

    • Search Google Scholar
    • Export Citation
  • GlossB Giannocco G Swanson EA Moriscot AS Chiellini G Scanlan T Baxter JD & Dillmann WH 2005 Different configurations of specific thyroid hormone response elements mediate opposite effects of thyroid hormone and GC-1 on gene expression. Endocrinology1464926–4933.

    • Search Google Scholar
    • Export Citation
  • GotheS Wang Z Ng L Kindblom JM Barros AC Ohlsson C Vennstrom B & Forrest D 1999 Mice devoid of all known thyroid hormone receptors are viable but exhibit disorders of the pituitary–thyroid axis growth and bone maturation. Genes and Development131329–1341.

    • Search Google Scholar
    • Export Citation
  • GroverGJ Egan DM Sleph PG Beehler BC Chiellini G Nguyen NH Baxter JD & Scanlan TS 2004 Effects of the thyroid hormone receptor agonist GC-1 on metabolic rate and cholesterol in rats and primates: selective actions relative to 353′-triiodo-l-thyronine. Endocrinology1451656–1661.

    • Search Google Scholar
    • Export Citation
  • IossaS Lionetti L Mollica MP Crescenzo R Barletta A & Liverini G 2001 Fat balance and serum leptin concentrations in normal hypothyroid and hyperthyroid rats. International Journal of Obesity and Related Metabolic Disorders25417–425.

    • Search Google Scholar
    • Export Citation
  • JohanssonC Vennstrom B & Thoren P 1998 Evidence that decreased heart rate in thyroid hormone receptor-alpha1-deficient mice is an intrinsic defect. American Journal of Physiology275R640–R646.

    • Search Google Scholar
    • Export Citation
  • JohanssonC Gothe S Forrest D Vennstrom B & Thoren P 1999 Cardiovascular phenotype and temperature control in mice lacking thyroid hormone receptor-beta or both alpha1 and beta. American Journal of Physiology276H2006–H2012.

    • Search Google Scholar
    • Export Citation
  • KatzD & Lazar MA 1993 Dominant negative activity of an endogenous thyroid hormone receptor variant (alpha 2) is due to competition for binding sites on target genes. Journal of Biological Chemistry26820904–20910.

    • Search Google Scholar
    • Export Citation
  • KongWM Martin NM Smith KL Gardiner JV Connoley IP Stephens DA Dhillo WS Ghatei MA Small CJ & Bloom SR 2004 Triiodothyronine stimulates food intake via the hypothalamic ventromedial nucleus independent of changes in energy expenditure. Endocrinology1455252–5258.

    • Search Google Scholar
    • Export Citation
  • LazarMA1993 Thyroid hormone receptors: multiple forms multiple possibilities. Endocrine Reviews14184–193.

  • LonnL Stenlof K Ottosson M Lindroos AK Nystrom E & Sjostrom L 1998 Body weight and body composition changes after treatment of hyperthyroidism. Journal of Clinical Endocrinology and Metabolism834269–4273.

    • Search Google Scholar
    • Export Citation
  • ManzanoJ Morte B Scanlan TS & Bernal J 2003 Differential effects of triiodothyronine and the thyroid hormone receptor beta-specific agonist GC-1 on thyroid hormone target genes in the brain. Endocrinology1445480–5487.

    • Search Google Scholar
    • Export Citation
  • MiyabaraEH Aoki MS Soares AG Saltao RM Vilicev CM Passarelli M Scanlan TS Gouveia CH & Moriscot AS 2005 Thyroid hormone receptor-beta-selective agonist GC-24 spares skeletal muscle type I to II fiber shift. Cell and Tissue Research321233–241.

    • Search Google Scholar
    • Export Citation
  • MollerN Nielsen S Nyholm B Porksen N Alberti KG & Weeke J 1996 Glucose turnover fuel oxidation and forearm substrate exchange in patients with thyrotoxicosis before and after medical treatment. Clinical Endocrinology44453–459.

    • Search Google Scholar
    • Export Citation
  • MorteB Manzano J Scanlan T Vennstrom B & Bernal J 2002 Deletion of the thyroid hormone receptor alpha 1 prevents the structural alterations of the cerebellum induced by hypothyroidism. PNAS993985–3989.

    • Search Google Scholar
    • Export Citation
  • MorteB Manzano J Scanlan TS Vennstrom B & Bernal J 2004 Aberrant maturation of astrocytes in thyroid hormone receptor alpha 1 knockout mice reveals an interplay between thyroid hormone receptor isoforms. Endocrinology1451386–1391.

    • Search Google Scholar
    • Export Citation
  • MotomuraK & Brent GA 1998 Mechanisms of thyroid hormone action. Implications for the clinical manifestation of thyrotoxicosis. Endocrinology and Metabolism Clinics of North America271–23.

    • Search Google Scholar
    • Export Citation
  • NicolCJ & Bruce DS 1981 Effect of hyperthyroidism on the contractile and histochemical properties of fast and slow twitch skeletal muscle in the rat. Pflügers Archiv39073–79.

    • Search Google Scholar
    • Export Citation
  • RefetoffS2003 The syndrome of resistance to thyroid stimulating hormone. Journal of the Chinese Medical Association66441–452.

  • RibeiroMO Carvalho SD Schultz JJ Chiellini G Scanlan TS Bianco AC & Brent GA 2001 Thyroid hormone–sympathetic interaction and adaptive thermogenesis are thyroid hormone receptor isoform–specific. Journal of Clinical Investigation10897–105.

    • Search Google Scholar
    • Export Citation
  • RiisAL Jorgensen JO Gjedde S Norrelund H Jurik AG Nair KS Ivarsen P Weeke J & Moller N 2005 Whole body and forearm substrate metabolism in hyperthyroidism: evidence of increased basal muscle protein breakdown. American Journal of Physiology. Endocrinology and Metabolism288E1067–E1073.

    • Search Google Scholar
    • Export Citation
  • dos SantosRA Giannocco G & Nunes MT 2001 Thyroid hormone stimulates myoglobin expression in soleus and extensorum digitalis longus muscles of rats: concomitant alterations in the activities of Krebs cycle oxidative enzymes. Thyroid11545–550.

    • Search Google Scholar
    • Export Citation
  • SoukupT Zacharova G Smerdu V & Jirmanova I 2001 Body heart thyroid gland and skeletal muscle weight changes in rats with altered thyroid status. Physiological Research50619–626.

    • Search Google Scholar
    • Export Citation
  • TrostSU Swanson E Gloss B Wang-Iverson DB Zhang H Volodarsky T Grover GJ Baxter JD Chiellini G Scanlan TS et al.2000 The thyroid hormone receptor-beta-selective agonist GC-1 differentially affects plasma lipids and cardiac activity. Endocrinology1413057–3064.

    • Search Google Scholar
    • Export Citation
  • WahrenbergH Wennlund A & Arner P 1994 Adrenergic regulation of lipolysis in fat cells from hyperthyroid and hypothyroid patients. Journal of Clinical Endocrinology and Metabolism78898–903.

    • Search Google Scholar
    • Export Citation
  • WhiteP Burton KA Fowden AL & Dauncey MJ 2001 Developmental expression analysis of thyroid hormone receptor isoforms reveals new insights into their essential functions in cardiac and skeletal muscles. FASEB Journal151367–1376.

    • Search Google Scholar
    • Export Citation
  • WikstromL Johansson C Salto C Barlow C Campos Barros A Baas F Forrest D Thoren P & Vennstrom B 1998 Abnormal heart rate and body temperature in mice lacking thyroid hormone receptor alpha 1. EMBO Journal17455–461.

    • Search Google Scholar
    • Export Citation
  • WithersPC1977 Measurement of VO2 VCO2 and evaporative water loss with a flow-through mask. Journal of Applied Physiology42120–123.

  • YuF Degens H Li X & Larsson L 1998 Gender- and age-related differences in the regulatory influence of thyroid hormone on the contractilityand myosin composition of single rat soleus muscle fibres. Pflügers Archiv43721–30.

    • Search Google Scholar
    • Export Citation

If the inline PDF is not rendering correctly, you can download the PDF file here.

 

      Society for Endocrinology

Sept 2018 onwards Past Year Past 30 Days
Abstract Views 0 0 0
Full Text Views 787 127 13
PDF Downloads 244 54 2
  • View in gallery

    Effects of T3 and GC-1 on body weight and food intake. (A) Body-weight response to treatment with T3. (B) Body-weight response to treatment with GC-1. Body weight was measured thrice a week in control rats and rats treated for 6 weeks with T3 or GC-1. (C) Food intake was determined weekly in control rats and rats treated for 6 weeks with T3 or GC-1. All values (A–C) are expressed as the mean ± s.e.m. (n = 8 per group). *P < 0.05 and P < 0.001, control vs 10×T3 and 20×T3 and P < 0.05, control vs 20×T3 by Student–Newman–Keuls test.

  • View in gallery

    Effects of T3 and GC-1 on oxygen consumption. Resting oxygen consumption was measured at the end of the experimental period in control rats and rats treated for 6 weeks with T3 or GC-1. All values are expressed as the mean ± s.e.m. (n = 5 per group). *P < 0.01 and P < 0.001 vs control by Student–Newman–Keuls test.

  • View in gallery

    Effects of T3 and GC-1 on change in fat mass, carcass fat content and retroperitoneal fat pad. All parameters were determined in control rats and rats treated for 6 weeks with T3 or GC-1. (A) ΔFat mass (final fat mass-basal fat mass) was determined in vivo by DEXA. (B) Carcass fat content. (C) Retroperitoneal fat pad. All values are expressed as the mean ± s.e.m. (n = 8 per group). *P < 0.05, P < 0.01 and P < 0.001 vs control by Student–Newman–Keuls test.

  • AngerasU & Hasselgren PO 1985 Protein turnover in different types of skeletal muscle during experimental hyperthyroidism in rats. Acta Endocrinologica10990–95.

    • Search Google Scholar
    • Export Citation
  • BaxterJD Webb P Grover G & Scanlan TS 2004 Selective activation of thyroid hormone signaling pathways by GC-1: a new approach to controlling cholesterol and body weight. Trends in Endocrinology and Metabolism15154–157.

    • Search Google Scholar
    • Export Citation
  • BertinE Ruiz JC Mourot J Peiniau P & Portha B 1998 Evaluation of dual-energy X-ray absorptiometry for body-composition assessment in rats. Journal of Nutrition1281550–1554.

    • Search Google Scholar
    • Export Citation
  • BiancoAC & Silva JE 1987 Nuclear 353′-triiodothyronine (T3) in brown adipose tissue: receptor occupancy and sources of T3 as determined by in vivo techniques. Endocrinology12055–62.

    • Search Google Scholar
    • Export Citation
  • BrooksSP Lampi BJ Sarwar G & Botting HG 1995 A comparison of methods for determining total body protein. Analytical Biochemistry22626–30.

    • Search Google Scholar
    • Export Citation
  • ChengSY2005 Thyroid hormone receptor mutations and disease: beyond thyroid hormone resistance. Trends in Endocrinology and Metabolism16176–182.

    • Search Google Scholar
    • Export Citation
  • ChielliniG Apriletti JW Yoshihara HA Baxter JD Ribeiro RC & Scanlan TS 1998 A high-affinity subtype-selective agonist ligand for the thyroid hormone receptor. Chemistry and Biology5299–306.

    • Search Google Scholar
    • Export Citation
  • DanziS & Klein I 2004 Thyroid hormone and the cardiovascular system. Minerva Endocrinologica29139–150.

  • DevorST & White TP 1995 Myosin heavy chain phenotype in regenerating skeletal muscle is affected by thyroid hormone. Medicine and Science in Sports and Exercise27674–681.

    • Search Google Scholar
    • Export Citation
  • FlamantF Poguet AL Plateroti M Chassande O Gauthier K Streichenberger N Mansouri A & Samarut J 2002 Congenital hypothyroid Pax8(−/−) mutant mice can be rescued by inactivating the TR alpha gene. Molecular Endocrinology1624–32.

    • Search Google Scholar
    • Export Citation
  • FolchJ Lees M & Sloane Stanley GH 1957 A simple method for the isolation and purification of total lipids from animal tissues. Journal of Biological Chemistry226497–509.

    • Search Google Scholar
    • Export Citation
  • FowlerPB McIvor J Sykes L & Macrae KD 1996 The effect of long-term thyroxine on bone mineral density and serum cholesterol. Journal of the Royal College of Physicians of London30527–532.

    • Search Google Scholar
    • Export Citation
  • FraichardA Chassande O Plateroti M Roux JP Trouillas J Dehay C Legrand C Gauthier K Kedinger M Malaval L et al.1997 The T3R alpha gene encoding a thyroid hormone receptor is essential for post-natal development and thyroid hormone production. EMBO Journal164412–4420.

    • Search Google Scholar
    • Export Citation
  • FreedmanLP1992 Anatomy of the steroid receptor zinc finger region. Endocrine Reviews13129–145.

  • FreitasFR Moriscot AS Jorgetti V Soares AG Passarelli M Scanlan TS Brent GA Bianco AC & Gouveia CH 2003 Spared bone mass in rats treated with thyroid hormone receptor TRβ-selective compound GC-1. American Journal of Physiology. Endocrinology and Metabolism285E1135–E1141.

    • Search Google Scholar
    • Export Citation
  • FreitasFR Capelo LP O’Shea PJ Jorgetti V Moriscot AS Scanlan TS Williams GR Zorn TM & Gouveia CH 2005 The thyroid hormone receptor beta-specific agonist GC-1 selectively affects the bone development of hypothyroid rats. Journal of Bone and Mineral Research20294–304.

    • Search Google Scholar
    • Export Citation
  • FurlowJD Yang HY Hsu M Lim W Ermio DJ Chiellini G & Scanlan TS 2004 Induction of larval tissue resorption in Xenopus laevis tadpoles by the thyroid hormone receptor agonist GC-1. Journal of Biological Chemistry27926555–26562.

    • Search Google Scholar
    • Export Citation
  • GauthierK Plateroti M Harvey CB Williams GR Weiss RE Refetoff S Willott JF Sundin V Roux JP Malaval L et al.2001 Genetic analysis reveals different functions for the products of the thyroid hormone receptor alpha locus. Molecular and Cellular Biology214748–4760.

    • Search Google Scholar
    • Export Citation
  • GlossB Giannocco G Swanson EA Moriscot AS Chiellini G Scanlan T Baxter JD & Dillmann WH 2005 Different configurations of specific thyroid hormone response elements mediate opposite effects of thyroid hormone and GC-1 on gene expression. Endocrinology1464926–4933.

    • Search Google Scholar
    • Export Citation
  • GotheS Wang Z Ng L Kindblom JM Barros AC Ohlsson C Vennstrom B & Forrest D 1999 Mice devoid of all known thyroid hormone receptors are viable but exhibit disorders of the pituitary–thyroid axis growth and bone maturation. Genes and Development131329–1341.

    • Search Google Scholar
    • Export Citation
  • GroverGJ Egan DM Sleph PG Beehler BC Chiellini G Nguyen NH Baxter JD & Scanlan TS 2004 Effects of the thyroid hormone receptor agonist GC-1 on metabolic rate and cholesterol in rats and primates: selective actions relative to 353′-triiodo-l-thyronine. Endocrinology1451656–1661.

    • Search Google Scholar
    • Export Citation
  • IossaS Lionetti L Mollica MP Crescenzo R Barletta A & Liverini G 2001 Fat balance and serum leptin concentrations in normal hypothyroid and hyperthyroid rats. International Journal of Obesity and Related Metabolic Disorders25417–425.

    • Search Google Scholar
    • Export Citation
  • JohanssonC Vennstrom B & Thoren P 1998 Evidence that decreased heart rate in thyroid hormone receptor-alpha1-deficient mice is an intrinsic defect. American Journal of Physiology275R640–R646.

    • Search Google Scholar
    • Export Citation
  • JohanssonC Gothe S Forrest D Vennstrom B & Thoren P 1999 Cardiovascular phenotype and temperature control in mice lacking thyroid hormone receptor-beta or both alpha1 and beta. American Journal of Physiology276H2006–H2012.

    • Search Google Scholar
    • Export Citation
  • KatzD & Lazar MA 1993 Dominant negative activity of an endogenous thyroid hormone receptor variant (alpha 2) is due to competition for binding sites on target genes. Journal of Biological Chemistry26820904–20910.

    • Search Google Scholar
    • Export Citation
  • KongWM Martin NM Smith KL Gardiner JV Connoley IP Stephens DA Dhillo WS Ghatei MA Small CJ & Bloom SR 2004 Triiodothyronine stimulates food intake via the hypothalamic ventromedial nucleus independent of changes in energy expenditure. Endocrinology1455252–5258.

    • Search Google Scholar
    • Export Citation
  • LazarMA1993 Thyroid hormone receptors: multiple forms multiple possibilities. Endocrine Reviews14184–193.

  • LonnL Stenlof K Ottosson M Lindroos AK Nystrom E & Sjostrom L 1998 Body weight and body composition changes after treatment of hyperthyroidism. Journal of Clinical Endocrinology and Metabolism834269–4273.

    • Search Google Scholar
    • Export Citation
  • ManzanoJ Morte B Scanlan TS & Bernal J 2003 Differential effects of triiodothyronine and the thyroid hormone receptor beta-specific agonist GC-1 on thyroid hormone target genes in the brain. Endocrinology1445480–5487.

    • Search Google Scholar
    • Export Citation
  • MiyabaraEH Aoki MS Soares AG Saltao RM Vilicev CM Passarelli M Scanlan TS Gouveia CH & Moriscot AS 2005 Thyroid hormone receptor-beta-selective agonist GC-24 spares skeletal muscle type I to II fiber shift. Cell and Tissue Research321233–241.

    • Search Google Scholar
    • Export Citation
  • MollerN Nielsen S Nyholm B Porksen N Alberti KG & Weeke J 1996 Glucose turnover fuel oxidation and forearm substrate exchange in patients with thyrotoxicosis before and after medical treatment. Clinical Endocrinology44453–459.

    • Search Google Scholar
    • Export Citation
  • MorteB Manzano J Scanlan T Vennstrom B & Bernal J 2002 Deletion of the thyroid hormone receptor alpha 1 prevents the structural alterations of the cerebellum induced by hypothyroidism. PNAS993985–3989.

    • Search Google Scholar
    • Export Citation
  • MorteB Manzano J Scanlan TS Vennstrom B & Bernal J 2004 Aberrant maturation of astrocytes in thyroid hormone receptor alpha 1 knockout mice reveals an interplay between thyroid hormone receptor isoforms. Endocrinology1451386–1391.

    • Search Google Scholar
    • Export Citation
  • MotomuraK & Brent GA 1998 Mechanisms of thyroid hormone action. Implications for the clinical manifestation of thyrotoxicosis. Endocrinology and Metabolism Clinics of North America271–23.

    • Search Google Scholar
    • Export Citation
  • NicolCJ & Bruce DS 1981 Effect of hyperthyroidism on the contractile and histochemical properties of fast and slow twitch skeletal muscle in the rat. Pflügers Archiv39073–79.

    • Search Google Scholar
    • Export Citation
  • RefetoffS2003 The syndrome of resistance to thyroid stimulating hormone. Journal of the Chinese Medical Association66441–452.

  • RibeiroMO Carvalho SD Schultz JJ Chiellini G Scanlan TS Bianco AC & Brent GA 2001 Thyroid hormone–sympathetic interaction and adaptive thermogenesis are thyroid hormone receptor isoform–specific. Journal of Clinical Investigation10897–105.

    • Search Google Scholar
    • Export Citation
  • RiisAL Jorgensen JO Gjedde S Norrelund H Jurik AG Nair KS Ivarsen P Weeke J & Moller N 2005 Whole body and forearm substrate metabolism in hyperthyroidism: evidence of increased basal muscle protein breakdown. American Journal of Physiology. Endocrinology and Metabolism288E1067–E1073.

    • Search Google Scholar
    • Export Citation
  • dos SantosRA Giannocco G & Nunes MT 2001 Thyroid hormone stimulates myoglobin expression in soleus and extensorum digitalis longus muscles of rats: concomitant alterations in the activities of Krebs cycle oxidative enzymes. Thyroid11545–550.

    • Search Google Scholar
    • Export Citation
  • SoukupT Zacharova G Smerdu V & Jirmanova I 2001 Body heart thyroid gland and skeletal muscle weight changes in rats with altered thyroid status. Physiological Research50619–626.

    • Search Google Scholar
    • Export Citation
  • TrostSU Swanson E Gloss B Wang-Iverson DB Zhang H Volodarsky T Grover GJ Baxter JD Chiellini G Scanlan TS et al.2000 The thyroid hormone receptor-beta-selective agonist GC-1 differentially affects plasma lipids and cardiac activity. Endocrinology1413057–3064.

    • Search Google Scholar
    • Export Citation
  • WahrenbergH Wennlund A & Arner P 1994 Adrenergic regulation of lipolysis in fat cells from hyperthyroid and hypothyroid patients. Journal of Clinical Endocrinology and Metabolism78898–903.

    • Search Google Scholar
    • Export Citation
  • WhiteP Burton KA Fowden AL & Dauncey MJ 2001 Developmental expression analysis of thyroid hormone receptor isoforms reveals new insights into their essential functions in cardiac and skeletal muscles. FASEB Journal151367–1376.

    • Search Google Scholar
    • Export Citation
  • WikstromL Johansson C Salto C Barlow C Campos Barros A Baas F Forrest D Thoren P & Vennstrom B 1998 Abnormal heart rate and body temperature in mice lacking thyroid hormone receptor alpha 1. EMBO Journal17455–461.

    • Search Google Scholar
    • Export Citation
  • WithersPC1977 Measurement of VO2 VCO2 and evaporative water loss with a flow-through mask. Journal of Applied Physiology42120–123.

  • YuF Degens H Li X & Larsson L 1998 Gender- and age-related differences in the regulatory influence of thyroid hormone on the contractilityand myosin composition of single rat soleus muscle fibres. Pflügers Archiv43721–30.

    • Search Google Scholar
    • Export Citation