RESUMO
Hypothyroidism and thyrotoxicosis produce adverse effects in male reproduction by unknown mechanisms. We investigated whether triiodothyronine (T3) modulates luteinizing hormone (LH) and follicle stimulating hormone (FSH) synthesis/secretion, by inducing different thyroid states. In hypothyroidism, the content of Lhb and Fshb mRNAs was increased, while their association to ribosomes and the protein content were reduced and the serum LH and FSH concentrations were augmented and decreased, respectively. Thyrotoxicosis reduced Lhb mRNA and LH serum concentration, and increased Lhb mRNA translational rate. The Fshb mRNA content and its association to ribosomes were also increased, whereas FSH serum concentrations were comparable to euthyroid levels. Acute T3 treatment decreased the total content of Lhb and Fshb mRNAs, and increased their association to ribosomes, as well as the LHB and FSHB contents in secretory granules. This study shows that T3 acts on gonadotrophs, resulting in direct effects on LH and FSH synthesis/secretion of male rats, suggesting that some reproductive disorders observed in men may be associated with thyroid hormone imbalances.
Assuntos
Hormônio Foliculoestimulante/genética , Hormônio Foliculoestimulante/metabolismo , Hormônio Luteinizante/genética , Hormônio Luteinizante/metabolismo , Tri-Iodotironina/farmacologia , Animais , Expressão Gênica/efeitos dos fármacos , Hipotireoidismo/genética , Hipotireoidismo/metabolismo , Masculino , RNA Mensageiro/metabolismo , Ratos , Ratos Wistar , TireoidectomiaRESUMO
TSH, FSH and LH share the same glycoprotein alpha chain (CGA) as part of their protein structure. Therefore, it is possible that thyroid and gonadal dysfunction may affect the CGA expression. This study evaluated several steps of CGA synthesis and secretion in thyrotrophs and gonadotrophs of control and hypothyroid rats, acutely or chronically-treated with T3. Hypothyroidism increased the Cga mRNA expression and its association to ribosome, but decreased intracellular CGA content. These parameters were reversed after acute or chronic T3 treatment. We conclude that T3 not only down-regulates Cga mRNA expression, as expected, but also inhibits the association of Cga mRNA to ribosome, as well as the CGA secretion. These findings add novel insights into our understanding of the role of T3 on the regulation of the Cga gene expression and CGA secretion, which might have a potential repercussion in all pituitary glycoprotein hormone synthesis and secretion.
Assuntos
Subunidade alfa de Hormônios Glicoproteicos/genética , Subunidade alfa de Hormônios Glicoproteicos/metabolismo , Hipotireoidismo/tratamento farmacológico , Adeno-Hipófise/metabolismo , Tri-Iodotironina/administração & dosagem , Animais , Modelos Animais de Doenças , Hormônio Foliculoestimulante/metabolismo , Regulação da Expressão Gênica/efeitos dos fármacos , Gonadotrofos/metabolismo , Hipotireoidismo/metabolismo , Hormônio Luteinizante/metabolismo , Masculino , Ratos , Ratos Wistar , Ribossomos/genética , Tireotrofos/metabolismo , Tireotropina/metabolismo , Tri-Iodotironina/farmacologiaRESUMO
Rapid actions of T3 on TSH synthesis in posttranscriptional steps, such as polyadenylation and translation rate, have already been described. The focus of this paper was to characterize rapid actions of T3 on TSH secretion and the involvement of actin and microtubule cytoskeleton in this process. For that, sham-operated (SO) and thyroidectomized (Tx) rats were subjected to acute or chronic treatment with T3. We observed a disarrangement in microtubule and actin cytoskeletons and an increase in Tshb mRNA levels in Tx rats, whereas the total TSH protein content was reduced in the pituitary gland as a whole, but increased in the secretory granules close to the plasma membrane of thyrotrophs, as well as in the extracellular space. The acute T3 dose promoted a rapid increase and redistribution of TSH secretory granules throughout the cytoplasm, as well as a rearrangement in actin and microtubule cytoskeletons. The T3 chronic treatment outcome reinforces the acute effects observed and, additionally, evinces an increase in the α-tubulin content and a rearrangement in microtubule cytoskeleton. Thus, T3 is able to rapidly suppress TSH secretion and, in parallel, to promote a rearrangement in actin and microtubules assembly throughout the pituitary gland, effects that seem to be independent from each other.
Assuntos
Citoesqueleto/fisiologia , Vesículas Secretórias/fisiologia , Tireotrofos/citologia , Tireotropina/metabolismo , Tri-Iodotironina/farmacologia , Actinas/metabolismo , Animais , Masculino , Ratos , Ratos Wistar , Tireoidectomia , Tireotrofos/metabolismo , Tireotropina Subunidade beta/genética , Tireotropina Subunidade beta/metabolismoRESUMO
BACKGROUND: Studies in men are not consistent regarding the effects of thyroid hormone on the production of gonadotropins. In hypothyroidism consequent to diverse causes, an increase or no change in serum luteinizing hormone (LH) have been reported. The attempt to explain the mechanisms involved in this pathology using rats as an experimental model also seems to repeat this divergence, since hypothyroidism has been shown to induce hypogonadotropic hypogonadism, a hypergonadotropic state, or not to affect the basal levels of LH. Notably, the promoter region of the gene encoding the Lh beta subunit and GnRH (gonadotropin-releasing factor) does not contain a thyroid responsive element. Therefore, we investigated the hypothesis that, in male rats, posttranscriptional mechanisms of LH synthesis are altered in hypothyroidism. We also attempted to determine if hypothyroidism directly affects testicular function in male rats. METHODS: Male Wistar rats, 60 days old, were thyroidectomized or sham-operated. After 20 days, they were decapitated, and the pituitaries were collected and analyzed for Lh mRNA, LH content, poly(A) tail length, and polysome profile. The testes were collected and analyzed for Lh receptor mRNA, LH receptor content, and histology using morphometric analyses. The testis, epididymis, seminal vesicle, and ventral prostate were weighed, and serum concentrations of LH, testosterone, thyrotropin (TSH), and triiodothyronine (T3) were measured. RESULTS: Hypothyroidism was associated, in the pituitary, with an increase in Lh mRNA expression, a reduction in Lh mRNA poly(A) tail length, a reduction in the number of LH transcripts associated with polysomes. Pituitary LH was decreased but serum LH was increased from 102 to 543 pg/mL. Despite this, serum testosterone concentrations were decreased from 1.8 to 0.25 ng/mL. A decreased germinative epithelium height of the testes and a reduced weight of androgen-responsive tissues were observed (ventral prostrate: 74 vs. 23 mg/100 g body weight [BW]; seminal vesicle undrained: 280 vs. 70 mg/100 g BW; and seminal vesicle drained: 190 vs. 60 mg/100 g BW). CONCLUSIONS: Hypothyroidism in adult male rats has dual effects on the pituitary testicular axis. It alters posttranscriptional mechanisms of LH synthesis and probably has a direct effect on testicular function. However, these data suggest the possibility that reduced LH bioactivity may account in part for impaired testicular function.
Assuntos
Hipotireoidismo/metabolismo , Hormônio Luteinizante/biossíntese , Hipófise/metabolismo , Animais , Epididimo/metabolismo , Hormônio Liberador de Gonadotropina/genética , Hormônio Liberador de Gonadotropina/metabolismo , Hipotireoidismo/genética , Hormônio Luteinizante/sangue , Masculino , Próstata/metabolismo , RNA Mensageiro/genética , RNA Mensageiro/metabolismo , Ratos , Ratos Wistar , Testículo/metabolismo , TireoidectomiaRESUMO
BACKGROUND: Glucose transporter 4 (GLUT4) is highly expressed in muscle and fat tissue, where triiodothyronine (T(3)) induces solute carrier family 2 facilitated glucose transporter member 4 (SLC2A4) gene transcription. T(3) was also shown to rapidly increase glucose uptake in myocytes exposed to cycloheximide, indicating that it might act nongenomically to regulate GLUT4 availability. We tested this hypothesis by evaluating, in thyroidectomized rats (Tx rats), the acute and/or chronic T(3) effects on GLUT4 mRNA expression and polyadenylation, protein content, and trafficking to the plasma membrane (PM) in skeletal muscle, as well as on blood glucose disappearance rate (kITT) after insulin administration. METHODS: Rats were surgically thyroidectomized and treated with T(3) (0.3 to 100 µg/100 g body weight) from 10 minutes to 5 days, and killed thereafter. Sham-operated (SO) rats were used as controls. Total RNA was extracted from the skeletal muscles (soleus [SOL] and extensorum digitalis longus [EDL]) and subjected to Northern blotting analysis using rat GLUT4 cDNA probe. Total protein was extracted and subjected to specific centrifugations for subcellular fractionation, and PM as well as microsomal (M) fractions were subjected to Western blotting analysis, using anti-GLUT4 antiserum as a probe. GLUT4 mRNA polyadenylation was examined by a rapid amplification of cDNA ends-poly(A) test (RACE-PAT). RESULTS: Thyroidectomy reduced skeletal muscle GLUT4 mRNA, mRNA poly(A) tail length, protein content, and trafficking to the PM, as well as the kITT. The acute T(3) treatment rapidly (30 minutes) increased all these parameters compared with Tx rats. The 5-day T(3) treatment increased GLUT4 mRNA and protein expression, and restored GLUT4 trafficking to the PM and kITT to SO values. CONCLUSIONS: The results presented here show for the first time that, in parallel to its transcriptional action on the SLC2A4 gene, T(3) exerts a rapid post-transcriptional effect on GLUT4 mRNA polyadenylation, which might increase transcript stability and translation efficiency, leading to the increased GLUT4 content and availability to skeletal muscle, as well as on GLUT4 translocation to the PM, improving the insulin sensitivity, as shown by the kITT.