Abstract
The downregulation of liver deiodinase type 1 (D1) is supposed to be one of the mechanisms behind the decrease in serum tri-iodothyronine (T3) observed during non-thyroidal illness (NTI). Liver D1 mRNA expression is positively regulated by T3, mainly via the thyroid hormone receptor (TR)β1. One might thus expect that lacking the TRβ gene would result in diminished downregulation of liver D1 expression and a smaller decrease in serum T3 during illness. In this study, we used TRβ−/− mice to evaluate the role of TRβ in lipopolysaccharide (LPS, a bacterial endotoxin)-induced changes in thyroid hormone metabolism. Our results show that the LPS-induced serum T3 and thyroxine and liver D1 decrease takes place despite the absence of TRβ. Furthermore, we observed basal differences in liver D1 mRNA and activity between TRβ−/− and wild-type mice and TRβ−/− males and females, which did not result in differences in serum T3. Serum T3 decreased rapidly after LPS administration, followed by decreased liver D1, indicating that the contribution of liver D1 during NTI may be limited with respect to decreased serum T3 levels. Muscle D2 mRNA did not compensate for the low basal liver D1 observed in TRβ−/− mice and increased in response to LPS in TRβ−/− and WT mice. Other (TRβ independent) mechanisms like decreased thyroidal secretion and decreased binding to thyroid hormone-binding proteins probably play a role in the early decrease in serum T3 observed in this study.
Introduction
Lipopolysaccharide (LPS, a bacterial endotoxin) administration is a well-established animal model for non-thyroidal illness (NTI; Boelen et al. 1995) via the induction of an acute phase inflammatory response (Palsson-McDermott & O'Neill 2004). This inflammatory response is accompanied by a decrease in liver type 1 deiodinase (D1) mRNA and activity and a decrease in serum tri-iodothyronine (T3) and thyroxine (T4), all characteristic of NTI (Boelen et al. 2004). Using this animal model, we have previously reported that liver TRβ1 mRNA decreased rapidly after LPS administration (Boelen et al. 2004), which was followed by a decrease in liver TRβ1 protein expression (Beigneux et al. 2003). In addition, in vitro studies in a hepatoma cell line have shown that the proinflammatory cytokine IL-1β induces a decrease in TRβ1 mRNA, which is mediated via the nuclear factor (NF)-κB inflammatory pathway. IL-1β also results in decreased D1 mRNA expression in vitro (Yu & Koenig 2000, Jakobs et al. 2002), which is mediated via the NF-κB and activator protein (AP)-1 inflammatory pathways simultaneously, suggesting different regulatory mechanisms (Kwakkel et al. 2006). A possible mechanism thought to be responsible for the observed D1 mRNA decrease is the competition for limiting amounts of steroid receptor coactivator-1 (Yu & Koenig 2000). The downregulation of liver D1 mRNA is supposed to be one of the mechanisms behind the LPS-induced decrease in serum T3 (Yu & Koenig 2006). D1 mRNA expression is positively regulated by T3 via the TRs, which activates gene transcription by binding to two thyroid hormone responsive elements (TREs) in the promoter region of the human D1 gene (Toyoda et al. 1995, Jakobs et al. 1997). Although no TREs have been identified in the promoter region of the mouse D1 gene, liver D1 in mice is upregulated by T3 administration and downregulated in hypothyroidism (Amma et al. 2001). In liver, D1 is mainly regulated via the TRβ1. In the absence of TRβ, liver D1 mRNA expression is decreased, although TRα1 partly takes over the T3-mediated D1 mRNA expression (Amma et al. 2001, Macchia et al. 2001). It is however unknown whether lacking the TRβ gene results in diminished downregulation of liver D1 mRNA expression and activity induced by LPS. In this study, we used TRβ−/− mice to evaluate the role of TRβ in LPS-induced changes in thyroid hormone metabolism.
Materials and Methods
Animal experiments
Male and female TRβ−/− and wild-type (WT; 129Sv/Ev) mice were used at 6–12 weeks of age. TRβ-/− were generated as described previously (Gauthier et al. 1999). Homozygous TRβ−/− mice were derived from heterozygous mothers to prevent the intra-uterine effects of the homozygous genotype. The WT and TRβ−/− mice were crossed and bred separately. The mice were kept in 12 h light:12 h darkness cycles in a temperature-controlled room. Acute illness was induced by an i.p. injection of 200 μg (LPS, Escherichia coli O127:B8; Sigma) diluted in 0.5 ml saline. Control mice received 0.5 ml saline. Due to diurnal variations (Zandieh et al. 2002), each time point had its own control and the experiment started at 0900 h. At time points 0, 4, 8, and 24 h after LPS or saline administration, two females and four males mice per group (two females and two to four males per group for t=24) were anaesthetized by i.p. injection of 100 mg/kg ketamine (Virbac, Carros Cedex, France) and 2 mg/kg xylazine (Bayer) and killed by cervical dislocation. Blood was taken by cardiac puncture and serum stored at −20 °C until analysis. Liver and hind limb muscle tissue were obtained and immediately stored in liquid nitrogen. The study was approved by the University Victor Segalen Animal Care and Use Committee.
Thyroid hormone levels
Serum T3 and T4 were measured with in-house RIAs (Wiersinga & Chopra 1982). To prevent inter-assay variation (T3, 6.2% and T4, 7.3%), all samples of one experiment were measured within the same assay (intra-assay variability T3, 3.6% and T4, 6.6%).
RNA isolation and RT-PCR
Liver and muscle mRNA was isolated with Magna Pure (Roche Molecular Biochemicals) using the Magna Pure LC mRNA tissue kit and ∼10 mg tissue. The protocol and buffers supplied with the corresponding kit were followed. cDNA synthesis was performed using the first strand cDNA synthesis kit for RT-PCR with oligo d(T) primers (Roche Molecular Biochemicals). Real-time PCR was performed using the LightCycler (Roche Molecular Biochemicals). For liver, PCR's LightCycler DNA master SYBR green I kit (Roche Molecular Biochemicals) was used, adding 3 mM MgCl2 and 50 ng primers (Biolegio, Nijmegen, The Netherlands) each. For muscle, PCR's LightCycler FastStart DNA MasterPlus SYBR green I kit (Roche Molecular Biochemicals) was used, adding 50 ng primers (Biolegio) each. Primer pairs for hypoxanthine phosphoribosyltransferase (HPRT), TRα1, D1, and IL-1β were previously described (Bouaboula et al. 1992, Bakker 2001, Sweet et al. 2001, Boelen et al. 2004). We designed primer pairs for D2 (D2 forward: 5′-GCT TCC TCC TAG ATG CCT ACA A-3′, D2 reverse: 5′-CCG AGG CAT AAT TGT TAC CTG-3′). Primers were intron spanning or genomic DNA contamination was tested using a cDNA synthesis reaction without the addition of reverse transcriptase. PCR programs were as follows: denaturation 30 s 95 °C, 40–45 cycles of 0–10 s 95 °C, 10 s annealing temperature, 72 °C, 15–20 s. For PCRs using FastStart, the denaturation time was extended to 10 min. Annealing temperatures were as follows: 54 °C for HPRT, 64 °C for TRα1, 52 °C for D1, 55 °C for D2, and 60 °C for IL-1β. For quantification, a standard curve was generated of a sequence-specific PCR product ranging from 0.01 fg/μl to 100 fg/μl (measurements taken during the exponential phase of amplification). Samples were corrected for their mRNA content using HPRT as a housekeeping gene. The samples were individually checked for their PCR efficiency (Ramakers et al. 2003). The median of the efficiency was calculated for each assay, and the samples that differed more than 0.05 of the efficiency median value were not taken into account (0% for liver TRα1, 2.5% for liver IL-1β and muscle D2, and 4% for liver D1). Aberrant PCR efficiencies occurred randomly and therefore did not bias the results.
Deiodinase activity
D1 activity was analyzed as described previously (Peeters et al. 2003). Samples were homogenized on ice in ten volumes of PED10 buffer (0.1 M sodium phosphate, 2 mM EDTA, and 10 mM dithiothreitol (DTT) pH 7.2)) using a Polytron (Kinematica, Luzern, Switzerland). Homogenates were snap frozen and stored at −80 °C until use. Protein concentration was measured with the Bio-Rad protein assay using BSA as the standard following the manufacturer's instructions (Bio-Rad Laboratories). Liver D1 activity was measured in duplicate, using 50 μl homogenate incubated in a final volume of 0.1 ml with 0.1 μM rT3 with the addition of ∼1×105 c.p.m. [3′5′-125I]rT3 in PED10. Reactions were stopped by adding 0.1 ml of 5% BSA on ice. The protein-bound iodothyronines were precipitated by the addition of 10% (w/v) trichloroacetic acid. After centrifugation, 125I− was separated from the supernatant by chromatography on Sephadex LH-20 columns with a bed volume of 0.25 ml, equilibrated, and eluted with 0.1 M HCl. Released 125I was counted using the Packard Cobra Auto-Gamma Counting System (Canberra Packard, Zürich, Switzerland) in the eluate. D1 activity was expressed as 125I pmol released per minute per mg liver protein.
D2: Muscle D2 activity was measured as described previously (Mebis et al. 2007). Samples were homogenized on ice in ten volumes of PED25 buffer (0.1 M sodium phosphate, 2 mM EDTA, and 25 mM DTT (pH 7.2)) using a Polytron (Kinematica, Luzern, Switzerland). Homogenates were used immediately. Protein concentration was measured with the Bio-Rad protein assay using BSA as the standard following the manufacturer's instructions (Bio-Rad Laboratories). D2 activity was measured in duplicate, using 50 μl (≈100 μg protein) homogenate incubated 4 h at 37 °C in a final volume of 0.1 ml with 1 nM T4 with the addition of ∼1×105 c.p.m. [3′5′-125I]T4 in PED25. Reactions were stopped by adding 0.1 ml ice-cold methanol. After centrifugation, 0.1 ml supernatant was added to 0.1 ml of 0.02 M ammonium acetate (pH 4), and 0.1 ml mixture was applied to 4.6×250 mm Symmetry C18 column connected to an Alliance HPLC system (Waters, Etten-Leur, The Netherlands). The column was eluted with a linear gradient of acetonitrile (28–42% in 15 min) in 0.02 M ammonium acetate (pH 4.0) at a flow of 1.2 ml/min. The activity of T4 and T3 in the eluate was measured online using a Radiomatic Z-500 flow scintillation detector (Packard, Meriden, CT, USA). D2 activity was expressed as fmol generated T3 per minute per gram muscle tissue.
Statistical analysis
Normal distribution of the data was tested using the Shapiro–Wilk test. Statistical significance between treatments and genotypes were evaluated using two-way ANOVA with two grouping factors (time and treatment, time and genotype; SPSS, Chicago, IL, USA). P values in the figures represent the significant effect of treatment or genotype. To test pair-wise comparisons, ANOVA was followed by Student's t-test (Excel Microsoft) when data were normally distributed or Mann–Whitney U tests (SPSS) when not normally distributed. The symbols in the figures represent the pair-wise P values. P<0.05 was considered statistically significant.
Results
Basal levels of thyroid hormones, deiodinases, and TRα1 mRNA
For the analysis of the basal values t=0 and 24 h saline groups were pooled (Table 1). Basal serum T3 and T4 levels were significantly higher in TRβ−/− mice compared with WT. Sex differences were not observed between male and female mice. Liver D1 mRNA and activity was significantly lower in TRβ−/− mice compared with WT. The lower expression of D1 mRNA was more pronounced in male TRβ−/− mice than that in female TRβ−/− mice, while no sex difference was observed in WT mice. In WT mice, liver TRα1 mRNA expression was higher in females than that in males, whereas this difference was absent in the TRβ−/− mice, resulting in a significant difference between female TRβ−/− compared with WT mice. Basal muscle D2 mRNA levels were not significantly different between TRβ−/− and WT mice; furthermore, no sex difference was observed. Muscle D2 activity was not detectable.
Basal laboratory values of thyroid hormone receptor (TRβ−/−) and wild-type (WT) mice. Mean values±s.e.m. are given
| Wild-type | TRβ−/− | |||
|---|---|---|---|---|
| ♀ | ♂ | ♀ | ♂ | |
| Serum T3 (nmol/l) | 1.55±0.34 | 1.34±0.14 | 2.53±0.24* | 2.68±0.21† |
| Serum T4 (nmol/l) | 67±6 | 57±4 | 133±14* | 151±16† |
| Liver D1 mRNA (a.u.) | 2.48±0.17 | 2.14±0.52 | 0.98±0.08†,‡ | 0.09±0.03† |
| Liver D1 activity (pmol/min per mg protein) | 5.34±0.5 | 5.0±0.6 | 2.5±0.3*,‡ | 0.1±0.02† |
| Muscle D2 mRNA (a.u.) | 0.091±0.028 | 0.145±0.058 | 0.216±0.064 | 0.163±0.120 |
| Liver TRα1 mRNA (a.u) | 0.75±0.06‡ | 0.39±0.04 | 0.52±0.00* | 0.38±0.05 |
Significances were evaluated by Student's t-test or Mann–Whitney U test when appropriate.*P≤0.05 and †P≤0.01 TRβ−/− compared with wild-type. ‡P≤0.01 females compared with males.
Effects of LPS administration on serum thyroid hormone levels
LPS-treated WT mice were compared with saline-treated WT mice. As expected, serum T3 and T4 significantly decreased after LPS administration (T3, P<0.05 and T4, P<0.01). LPS administration in TRβ−/− mice also resulted in decreased serum T3 and T4 compared with saline-treated TRβ−/− mice (T3, P<0.01 and T4, P<0.05). Serum T3 significantly decreased 4 (only TRβ−/−), 8, and 24 h after LPS administration, whereas T4 decreased significantly after 8 h. No significant difference was observed in the relative serum T3 and T4 decrease after LPS administration between TRβ−/− and WT mice. The results are shown in Fig. 1.
Relative values of serum T3 and T4 after 0, 4, 8, and 24 h in (A) saline-treated (▪) and LPS-treated (•) WT mice; (B) saline-treated (□) and LPS-treated (○) TRβ−/− mice; and (C) LPS-treated WT (•) and TRβ−/− (○) mice. Mean values±s.e.m. (n=4/6) are shown. P values indicate differences between groups by ANOVA. Significances of separate time points were evaluated by Student's t-tests; *P≤0.05, **P≤0.01.
Citation: Journal of Endocrinology 197, 1; 10.1677/JOE-07-0601
Effects of LPS administration on liver D1, TRα1, and IL-1β expression
No significant difference was observed in liver IL-1β mRNA expression after LPS administration between the WT and TRβ−/− mice, indicating a similar inflammatory response after LPS administration (data not shown). Liver D1 mRNA expression decreased in WT and TRβ−/− mice 8 and 24 h after LPS administration (P<0.01). Liver D1 activity decreased significantly 24 h after LPS administration in WT mice compared with saline-treated controls. Liver D1 activity in TRβ−/− mice decreased 8 h but not 24 h after LPS administration, which is not in agreement with the observed decrease in mRNA levels. The discrepancy between WT and TRβ−/− mice at 24 h is caused by the large variation in D1 activity levels in TRβ−/− mice, which results in an abnormal distribution. Median values were not different (t=24; TRβ−/− mice: 77% of the basal value, WT mice: 67% of the basal value). The overall decrease in liver D1 mRNA expression and activity was not significantly different between TRβ−/− and WT mice.
Liver TRα1 mRNA was significantly decreased in the LPS-treated WT and TRβ−/− mice after 4, 8, and 24 h (P<0.01). Relative liver TRα1 mRNA returned to normal levels after 8 and 24 h of LPS treatment in TRβ−/− mice, while in WT mice TRα1 mRNA levels were still decreased (P<0.01). The results are shown in Fig. 2.
Relative values of liver D1 mRNA, liver D1 activity, and liver TRα1 mRNA expression after 0, 4, 8, and 24 h in (A) saline-treated (▪) and LPS-treated (•) WT mice; (B) saline-treated (□) and LPS-treated (○) TRβ−/− mice; and (C) LPS-treated WT (•) and TRβ−/− (○) mice. Mean values±s.e.m. (n=4/6) are shown. P values indicate differences between groups by ANOVA. Significances of separate time points were evaluated by Student's t-tests for TRα1 and Mann–Whitney U tests for D1; *P≤0.05, **P≤0.01.
Citation: Journal of Endocrinology 197, 1; 10.1677/JOE-07-0601
Effects of LPS administration on muscle D2 expression
LPS administration in WT and TRβ−/− mice resulted in increased muscle D2 mRNA expression compared with saline-treated WT and TRβ−/− mice (P<0.01). In WT mice, D2 mRNA significantly increased after 4, 8, and 24 h after LPS administration. In TRβ−/− mice, D2 mRNA significantly increased 24 h after LPS administration. The relative increase in muscle D2 mRNA was more pronounced in WT mice compared with TRβ−/− mice (P<0.01). The results are shown in Fig. 3. Muscle D2 activity was not detectable.
Relative values of muscle D2 mRNA expression after 0, 4, 8, and 24 h of LPS treatment in (A) saline-treated (▪) and LPS-treated (•) WT mice; (B) saline-treated (□) and LPS-treated (○) TRβ−/− mice; and (C) LPS-treated WT (•) and TRβ−/− (○) mice. Mean values±s.e.m. (n=4/6) are shown. P values indicate differences between groups by ANOVA. Significances of separate time points were evaluated by Mann–Whitney U tests; *P≤0.05, **P≤0.01.
Citation: Journal of Endocrinology 197, 1; 10.1677/JOE-07-0601
Discussion
In this study, we aimed to investigate whether the TRβ gene is involved in altered thyroid hormone metabolism during illness. To this end, we studied TRβ−/− and WT mice in an established animal model of NTI. TRβ−/− mice have a disturbed pituitary and hypothalamic feedback mechanism that results in high serum T3 and T4 levels, without decreased thyroid-stimulating hormone and thyrotropin-releasing hormone levels (Forrest et al. 1996, Gauthier et al. 1999, Nikrodhanond et al. 2006). Furthermore, it has been shown that these mice have low basal liver D1 mRNA expression and D1 activity (Amma et al. 2001, Macchia et al. 2001). The elevated basal serum T3 and T4 levels and low liver D1 mRNA expression and activity in TRβ−/− mice observed in our experiments are in line with these findings.
Despite the differences in basal levels, LPS administration resulted in similar relative decreases in serum T3 and T4 and liver D1 decrease in TRβ−/− and WT mice. WT and TRβ−/− mice had similar liver IL-1β mRNA levels, indicating that the inflammatory response to LPS might be the same in TRβ−/− and WT mice. Part of the illness-induced alterations might be due to diminished food intake, as it is known that prolonged fasting influences both peripheral and central thyroid hormone metabolism (Boelen et al. 2006). However, we study a model of acute illness that takes place within 24 h. LPS experiments using pair-fed control mice have shown that although T3 and T4 decrease after reduced food intake, T3 and T4 serum levels were significantly lower after LPS administration. Furthermore, it was shown that liver D1 mRNA was not or only marginally affected after 24 h of starvation (Boelen et al. 1996). Therefore, we conclude that the acute alterations shown in this study cannot be attributed to decreased food intake due to LPS administration.
No difference in time course of the relative serum T3 and T4 decrease after LPS administration could be observed between TRβ−/− and WT mice. We concluded that the absence of TRβ had no effect on the illness-induced serum T3 and T4 decrease. Because TRβ1 regulates D1 gene expression (Amma et al. 2001, Macchia et al. 2001), which is thought to be responsible for the decrease in serum T3 during illness (Yu & Koenig 2006), liver D1 mRNA expression and activity were evaluated. LPS administration resulted in a similar overall decrease in relative liver D1 mRNA expression and activity in both genotypes. However, LPS administration resulted in decreased D1 activity levels after 24 h in WT mice while we did not observe this in TRβ−/− mice. This is caused by biological variation in D1 levels in TRβ−/− mice. In addition, LPS also induced a more pronounced decrease in D1 activity levels in TRβ−/− mice compared with saline-treated controls at 8 h. Absolute D1 activity levels were low in TRβ−/− mice, and despite the fact that the relative decrease was not different, we cannot exclude the effect of LPS on D1 activity that might also be related to the absolute amount of D1 present.
From these observations, we concluded that the decrease in liver D1 mRNA and activity observed during illness is not mediated via the TRβ1. Although we cannot exclude the possibility that the TRβ-mediated declines in the WT are mimicked by compensatory mechanisms in the TRβ knockout mice.
Additionally, liver TRα1 mRNA expression was evaluated because TRα1 might compensate for the lack of TRβ1 in D1 regulation (Amma et al. 2001, Macchia et al. 2001). However, in TRβ−/− mice TRα1 seemed to return to normal levels more quickly after LPS administration, while D1 mRNA remained low, although we cannot exclude that TRα1 protein levels were still low 24 h after LPS administration. Recently, it has been shown that D1 is not essential as a determinant of serum T3 during euthyroidism in mice (Schneider et al. 2006). We observed a significant difference in liver D1 between TRβ−/− and WT mice and between TRβ−/− males and females, which was not reflected in serum T3 levels, supporting the observation made by Schneider et al.
Muscle D2 has been proposed to play a significant role in regulating serum T3 (Maia et al. 2005). Therefore, we evaluated whether muscle D2 might be responsible for the serum T3 decrease during NTI as was previously suggested (Peeters et al. 2005). However, LPS administration did not result in a D2 mRNA decrease; on the contrary, D2 mRNA increased in response to LPS in WT and TRβ−/− mice. D2 activity could not be detected. Our results were confirmed in a recent study by Mebis et al. (2007) who described an increase in muscle D2 mRNA and activity in muscle tissue of ICU patients. The muscle D2 mRNA increase was more pronounced in WT mice, indicating that the increase in response to LPS might be partly mediated by TRβ.
The question remains whether a decrease in liver D1 is responsible for the observed decrease in serum T3. The rapid decrease in serum T3, followed by decreased liver D1, suggests that other mechanisms play a role. It is known that 50% of the serum T3 in rodents is derived from the thyroid and 50% from peripheral conversion (Chanoine et al. 1993). We previously observed early effects on thyroidal gene expression in LPS-treated mice (Boelen et al. 2004), but this could only partly be responsible for the rapid serum T3 decrease observed in this study because the half-life of serum T3 is 10 h. The effects of LPS on thyroid hormone-binding proteins might also influence serum T3 levels shortly after LPS administration. It is known in humans that during the acute phase response serum levels of thyroid hormone-binding proteins quickly decrease, thereby also decreasing serum total thyroid hormone levels (Afandi et al. 2000, Wiersinga 2005). However, it is known that 24 h after LPS administration fT3 decreases, so the thyroid hormone-binding protein effect can only account for the early T3 decrease (Boelen et al. 1995). Interestingly, we observed that the low basal liver D1 mRNA expression and enzyme activity was more pronounced in male than in female TRβ−/− mice, while no sex difference was observed in WT mice. Although sex differences in liver D1 mRNA and activity have been described in rats (Harris et al. 1979, Miyashita et al. 1995) and mice (Riese et al. 2006), we only observed a sex difference in TRβ−/− and not in WT mice. Furthermore, no discrepancy was observed between D1 mRNA expression and D1 enzyme activity as described previously by Riese et al. (2006), which could be due to the different genetic background of the mice. The sex difference observed in the TRβ−/− mice might be the result of other transcription factors involved in the regulation of the D1 gene via the TRE when the TRβ is absent. The estrogen receptor (ER) seems a logical candidate for mediating sex differences. The ER and TR share a common half site in the consensus DNA-binding sequence. Furthermore, it has been reported for several genes that the ER and TR influence each other's transcriptional activity, both inhibitory and stimulatory (Vasudevan et al. 2002). This regulatory mechanism might be impaired when the TR is absent, which is clearly evident from the disturbed lordosis behavior of female TRβ−/− mice (Dellovade et al. 2000). In addition, it has been shown for the human growth hormone promoter that when the TR is absent, the ER can activate gene transcription by binding to the TRE (Graupner et al. 1991). It might be possible that when the TRβ is absent, the ER binds the TRE and regulates D1 mRNA expression in female TRβ−/− mice.
From this study, we can conclude that illness-induced serum T3 and T4 and liver D1 decrease takes place despite the absence of TRβ. Furthermore, the observed basal differences in liver D1 mRNA and activity did not result in the differences in serum T3. Serum T3 decreased rapidly after LPS administration, followed by decreased liver D1, indicating that the contribution of liver D1 during NTI may be limited with respect to the decreased serum T3 levels. It could be that the decrease in liver D1 might only be involved in the serum T3 decrease 24 h after LPS administration. Muscle D2 mRNA did not compensate for the low basal liver D1 observed in TRβ−/− and increased in response to LPS. Therefore, muscle D2 cannot be responsible for the observed serum T3 decrease during NTI. In this mouse model, it is most likely that the decreased thyroidal secretion and the decreased binding of thyroid hormone to thyroid hormone-binding proteins are involved in the early decrease in T3 and T4 after LPS administration, whereas the liver D1 decrease and downregulation of the HPT axis might be involved later in time.
Acknowledgements
We would like to thank the staff of the Laboratory of Endocrinology for measuring thyroid hormones. Dr M T Ackermans (Laboratory of Endocrinology) is thanked for technical assistance with the D2 activity measurements. This study was supported in part by a grant from the French Ministry of Research (OC).
Disclosure
References
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