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Min Lu and Reigh-Yi Lin

Although TSH is the main regulator of thyroid growth and function, TSH binding activity in fat has long been reported. Since the TSH receptor (TSHR) has been detected in both preadipocytes and adipocytes, we hypothesized that it may play a role in adipose differentiation. Here, we use an in vitro model of adipogenesis from mouse embryonic stem (ES) cells to define TSH function. Directed differentiation of ES cells into the adipose lineage can be achieved over a 3-week period. Although adipocyte differentiation is initiated early in the development of cultured ES cells, TSHR up-regulation is precisely correlated with terminal differentiation of those adipocytes. The adipocytes express TSHR on the cell surface and respond to TSH with increased intracellular cAMP production, suggesting the activation of the protein kinase A signaling pathway. To determine whether TSH impacts adipogenesis, we examined how adipocytes responded to TSH at various points during their differentiation from cultured ES cells. We found that TSH greatly increases adipogenesis when added in the presence of adipogenic factors. More importantly, our data suggest that TSH also stimulates adipogenesis in cultured ES cells even in the absence of adipogenic factors. This finding provides the first evidence of TSH being a pro-adipogenic factor that converts ES cells into adipocytes. It further highlights the potential of ES cells as a model system for use in the study of TSH's role in the regulation of physiologically relevant adipose tissue.

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A Boelen, J Kwakkel, DC Thijssen-Timmer, A Alkemade, E Fliers and WM Wiersinga

During illness, major changes in thyroid hormone metabolism and regulation occur; these are collectively known as non-thyroidal illness and are characterized by decreased serum triiodothyronine (T(3)) and thyroxine (T(4)) without an increase in serum TSH. Whether alterations in the central part of the hypothalamus-pituitary-thyroid (HPT) axis precede changes in peripheral thyroid hormone metabolism instead of vice versa, or occur simultaneously, is presently unknown. We therefore studied the time-course of changes in thyroid hormone metabolism in the HPT axis of mice during acute illness induced by bacterial endotoxin (lipopolysaccharide; LPS).LPS rapidly induced interleukin-1beta mRNA expression in the hypothalamus, pituitary, thyroid and liver. This was followed by almost simultaneous changes in the pituitary (decreased expression of thyroid receptor (TR)-beta2, TSHbeta and 5'-deiodinase (D1) mRNAs), the thyroid (decreased TSH receptor mRNA) and the liver (decreased TRbeta1 and D1 mRNA). In the hypothalamus, type 2 deiodinase mRNA expression was strongly increased whereas preproTRH mRNA expression did not change after LPS. Serum T(3) and T(4) fell only after 24 h.Our results suggested almost simultaneous involvement of the whole HPT axis in the downregulation of thyroid hormone metabolism during acute illness.

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I. M. D. JACKSON, C. R. M. PRENTICE and MARGARET T. McKIDDIE

Although the clinical association of hypothyroidism and diabetes mellitus is well known (Phair, Bondy & Abelson, 1965; Hecht & Gershberg, 1968) there have been few studies of glucose and insulin metabolism in hypothyroidism before and after treatment; this paper reports our findings in ten such subjects.

Ten patients (9 female, 1 male; aged 43–73 yr.) with obvious clinical hypothyroidism, due to primary thyroid failure confirmed by a combination of serum protein-bound iodine, radioactive iodine studies with thyroid-stimulating hormone stimulation (as appropriate) and thyroid antibody studies, were investigated. None were known to be diabetic. An oral glucose tolerance test (50 g.) before and after treatment was performed, venous blood being removed for determination of blood sugar and plasma insulin levels at 0, 30, 60, 90 and 120 min. The sugar was measured as total reducing substances in a Technicon auto-analyser and plasma insulin by the double antibody radioimmunoassay method of Hales

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Y. Chandrasekhar, M. K. Holland, M. J. D'Occhio and B. P. Setchell

ABSTRACT

Mature Merino rams were made hypothyroid by daily oral drenching with methylthiouracil or hyperthyroid by daily subcutaneous injections of thyroxine for 8 weeks. Neither hypothyroidism nor hyperthyroidism had any apparent effect on either spermatogenesis or daily sperm production, but motility of ejaculated spermatozoa and circulating testosterone concentrations were reduced in both conditions. The ratio of testosterone concentrations in plasma from the internal spermatic vein to those in peripheral blood plasma was higher in hyperthyroid (21·2 ± 3·5) than in control (11·1 ±4·4 and hypothyroid (7·6±1·4) rams. The basal secretion rate for testosterone was slightly lower in hypothyroid rams and testosterone responses to human chorionic gonadotrophin and after LH-releasing hormone (LHRH) were very much reduced. Basal serum LH levels were low in both hypothyroid and hyperthyroid rams compared with controls whereas there were no differences in FSH levels. The LH response to exogenous LHRH was reduced in hypothyroid rams but not in hyperthyroid rams. Serum prolactin levels on the other hand were higher than control in both hypothyroid and hyperthyroid rams.

Reduced testosterone secretion in hypothyroid rams indicates that the normal function of Leydig cells depends on an adequate level of thyroid hormones. The decrease in circulating testosterone concentrations in hyperthyroid rams with normal secretion rates suggests an increased testosterone clearance rate in these animals. The decreased spermatozoal motility in hypo- and hyperthyroid rams suggests that the lowered testosterone level in these animals has altered the androgen-dependent maturation of spermatozoa in the epididymis. Changes in testis function together with decreased LH secretion in hypothyroid rams indicate that thyroid hormones can act at both the pituitary gland and testes to influence reproductive function in mature rams.

J. Endocr. (1985) 105, 39–46

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D. I. R. JONES

Metronidazole (1-β-hydroxyethyl-2-methyl-5-nitroimidazole; Flagyl, May & Baker Ltd.), an effective trichomonicidal agent, has recently been credited with widespread metabolic and endocrine effects including biochemical and clinical improvement of thyrotoxicosis (Taylor, 1962, 1965). Harden, Chisholm & Cant (1967), however, found no antithyroid action in either healthy volunteers or thyrotoxic patients but noted improvement of exophthalmos in 9 of 13 patients. The present trial was undertaken to establish the effect of metronidazole on exophthalmos.

Twenty thyrotoxic patients were selected; all had established exophthalmos with a minimum exophthalmometer reading of 20 mm. The patients had all been treated for thyrotoxicosis between 1·5 and 17 yr. previously (mean 5·9 yr.), either with radioactive iodine (14), surgically (3) or with antithyroid drugs (3). At the time of inclusion in the trial 6 patients were euthyroid and 11 were hyperthyroid and receiving antithyroid drugs; three had become hypothyroid after radioactive iodine therapy and were receiving thyroxine.

A

Free access

CA Isman, BC Yegen and I Alican

Depression of metabolism by hypothyroidism decreases oxidant production and thus protects tIssues against oxidant damage. Moreover, it is well-known that abnormal gut motility is a common manifestation in hypo/hyperthyroidism. In this study, we aimed to investigate the putative beneficial effects of methimazole on oxidative injury and dysmotility in a rat colitis model. Methimazole (0.04%) was administered in drinking water starting 15 days prior to induction of colitis. Colitis was induced by intracolonic administration of trinitrobenzene sulfonic acid (30 mg/ml; 0.8 ml) in ethanol. Six days after the induction of colitis, the fecal output was measured and used as an index for colonic motility. All rats were decapitated on the seventh day. The distal colon was weighed and the mucosal lesions were scored. Colonic lipid peroxidation (LP) and glutathione (GSH) measurements were performed. The macroscopic score, the colonic wet weight and LP values of the euthyroid colitis group were found to be higher than those of the control group (P<0.05-0.001). All these parameters were reduced in the methimazole-treated colitis group (P<0.01-0.001). The decrease in colonic GSH levels in the colitis group was completely abolished in the methimazole-treated colitis rats (P<0.01). Induction of colitis increased the average fecal output compared with the control group (P<0.05) and methimazole in the colitis group exaggerated the fecal output (P<0.001). In conclusion, methimazole reduces colonic oxidative injury probably due to hypometabolism, which is associated with a decrease in the production of reactive oxygen intermediates and an increase in the response of antioxidant systems.

Free access

Luana Lopes Souza, Aline Cordeiro, Lorraine Soares Oliveira, Gabriela Silva Monteiro de Paula, Larissa Costa Faustino, Tania Maria Ortiga-Carvalho, Karen Jesus Oliveira and Carmen Cabanelas Pazos-Moura

n-3 polyunsaturated fatty acids (n-3 PUFA) from fish oil (FO) exert important lipid-lowering effects, an effect also ascribed to thyroid hormones (TH) and TH receptor β1 (TRβ1)-specific agonists. n-3 PUFA effects are mediated by nuclear receptors, such as peroxisome proliferator-activated receptors (PPAR) and others. In this study, we investigated a role for TH signaling in n-3 PUFA effects. Euthyroid and hypothyroid adult rats (methimazole-treated for 5 weeks) received FO or soybean oil (control) by oral administration for 3 weeks. In euthyroid rats, FO treatment reduced serum triglycerides and cholesterol, diminished body fat, and increased protein content of the animals. In addition, FO-treated rats exhibited higher liver expression of TRβ1 and mitochondrial α-glycerophosphate dehydrogenase (mGPD), at protein and mRNA levels, but no alteration of glutathione S-transferase or type 1 deiodinase. In hypothyroid condition, FO induced reduction in serum cholesterol and increase in body protein content, but lost the ability to reduce triglycerides and body fat, and to induce TRβ1 and mGDP expression. FO did not change PPARα liver abundance regardless of thyroid state; however, hypothyroidism led to a marked increase in PPARα liver content but did not alter TRβ1 or TRα expression. The data suggest that part of the effect of n-3 PUFA from FO on lipid metabolism is dependent on TH signaling in specific steps and together with the marked upregulation of PPARα in liver of hypothyroid rats suggest important in vivo consequences of the cross-talking between those fatty acids and TH pathways in liver metabolism.

Free access

K De, G Ghosh, M Datta, A Konar, J Bandyopadhyay, D Bandyopadhyay, S Bhattacharya and A Bandyopadhyay

Experiments were carried out to identify the altered genes in hyperthyroid rat heart and their influence on the functions of cardiac myocytes. Chronic treatment of rats with 3,5,3' triiodo-L-thyronine (T3) resulted in a prominent increase in the size of the left ventricle with increased wall thickness and reduced chamber volume leading to concentric cardiac hypertrophy. The heart weight to body weight ratio (HW/BW) in hyperthyroid rats was increased by about 58% over that of normal rats. Using cDNA microarray comprising 588 genes, we compared the differences in mRNA expression of hyperthyroid and normal rat heart. Based on a threshold of greater than 10% change, about 37 genes were found to be regulated by T3. Further analyses by Western blotting, Northern blotting and real-time quantitative RT-PCR of some of the genes confirmed the microarray results. The T3-altered genes encode various types of proteins related to metabolism, matrix and cytoskeletal structures, growth factors, transcription factors, Ca(2+)-channels etc. The physiological significance of one of these altered proteins in hyperthyroid heart, insulin-responsive glucose transporter (GLUT) type 4 (GLUT4), was studied in detail. The expression of GLUT4 was drastically reduced in the ventricular tissues of hyperthyroid heart. Insulin-induced glucose uptake in hyperthyroid cardiomyocytes was reduced significantly, indicating the impaired glucose transport in cardiac cells. Interestingly, a few genes such as GLUT4, cytochrome P450 isoforms, superoxide dismutase (SOD), collagens, matrix metalloproteinases (MMP), tissue inhibitors of matrix metalloproteinases etc. which had not been reported earlier were found to be altered in hyperthyroid heart. Our results show some new aspects of hyperthyroid heart which will be important in assessing the pathophysiology of hypertrophied cardiomyocytes.

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J Rodriguez-Arnao, J Miell, M Thomas, A M McGregor and R J M Ross

Abstract

Changes in thyroid status have a major effect on the GH/insulin-like growth factor (IGF) axis. The majority of IGF in the circulation is bound to specific IGF-binding proteins (IGFBPs) of which six have been cloned and sequenced. We have studied changes in hepatic gene expression of IGFBP-1, -2 and -3, in male Wistar rats rendered hyperthyroid (thyroxine, 200 μg/kg per day) or hypothyroid (propylthiouracil, 0·1% daily). Littermates of the same age were used as controls (n=6 in each group). Thyroxine was measured by radioimmunoassay, and hepatic IGFBP-1, -2 and -3 mRNA levels by Northern blot analysis using specific rat cDNA probes with a 28S ribosomal probe as a loading control. Mean± s.e.m. thyroxine levels were 247·0±44·5 (hyperthyroid group), <9·0 (hypothyroid group) and 76·0 ± 4·5 nmol/l (control group). IGFBP-1 and -2 mRNA levels in the hypothyroid animals compared with the controls were significantly increased, but similar levels of expression were found in thyrotoxic and control rats. IGFBP-3 mRNA levels in hypothyroid animals were decreased, and increased in thyrotoxic animals. Thus, in the adult rat, hypothyroidism is associated with increased hepatic IGFBP-1 and -2 gene expression, but decreased IGFBP-3 gene expression, while in thyrotoxicosis there are normal IGFBP-1 and -2 mRNA levels but increased IGFBP-3 gene expression. These results suggest that there is specific and different transcriptional regulation for IGFBP-1, -2 and -3 in hypoand hyperthyroid rats.

Journal of Endocrinology (1994) 140, 251–255

Free access

Type 1 iodothyronine deiodinase in human physiology and disease

Deiodinases: the balance of thyroid hormone

Ana Luiza Maia, Iuri Martin Goemann, Erika L Souza Meyer and Simone Magagnin Wajner

Thyroid hormone is essential for the normal function of virtually all tissues. The iodothyronine deiodinases catalyze the removal of an iodine residue from the pro-hormone thyroxine (T4) molecule, thus producing either the active form triiodothyronine (T3; activation) or inactive metabolites (reverse T3; inactivation). Type I deiodinase (D1) catalyzes both reactions. Over the last years, several studies have attempted to understand the mechanisms of D1 function, underlying its effects on normal thyroid hormone metabolism and pathological processes. Although peripheral D1-generated T3 production contributes to a portion of plasma T3 in euthyroid state, pathologically increased thyroidal D1 activity seems to be the main cause of the elevated T3 concentrations observed in hyperthyroid patients. On the other hand, D1-deficient mouse models show that, in the absence of D1, inactive and lesser iodothyronines are excreted in feces with the loss of associated iodine, demonstrating the scavenging function for D1 that might be particularly important in an iodine deficiency setting. Polymorphisms in the DIO1 gene have been associated with changes in serum thyroid hormone levels, whereas decreased D1 activity has been reported in the nonthyroid illness syndrome and in several human neoplasias. The current review aims at presenting an updated picture of the recent advances made in the biochemical and molecular properties of D1 as well as its role in human physiology.