Effects of hypothyroidism on anti-mullerian hormone expression in the prepubertal rat testis

Differentiation of adult Leydig cells (ALC) in the prepubertal rat testis is stimulated by thyroid hormone (Thy) and inhibited by the Anti-Mullerian Hormone (AMH) produced by the immature Sertoli cell (SC). As Thy induces SC maturation in the prepubertal rat testis, we hypothesized that Thy stimulation of ALC differentiation is mediated via inhibition of AMH production by the SC with their maturation. If this hypothesis is true, AMH production by the prepubertal Sertoli cells in hypothyroid rats should not decline immediately after birth as in euthyroid rats, but should be maintained throughout the hypothyroid period at a similar or higher level to that of day 1 rats. This concept was tested using control rats of postnatal days (pd) 1, 7 and 14 and hypothyroid (fed 0.1% propyl thiouracil/PTU to lactating mothers) rats of pd7 and pd14. Presence of AMH in SC was examined by immunocytochemistry for AMH. Results demonstrated that testes of pd1 rats had intense AMH positive labeling exclusively in cytoplasm of SC. In testes of pd7 and pd14 control and PTU rats, a positive but weak labeling was also observed in cytoplasm of some SC; Germ cells and testicular interstitial cells were negative for AMH at all tested ages in both experimental groups. These findings suggest that AMH production by the prepubertal SC is independent of Sertoli cell maturation and not regulated by Thy. Therefore, Thy regulation of ALC differentiation in the prepubertal rat testis is unlikely to be mediated via inhibition of AMH produced by the SC with their maturation

Comparison of testis structure, function and thyroid hormone levels in control C57BL/6 mice and anti-mullerian hormone over expressing mice

Anti-Mullerian hormone (AMH) is considered as a negative regulator of postnatal Leydig cell (LC) differentiation, because AMH over expressing mice (Mt-hAMH mice) testes are deficient in LC. Therefore, in the present study Mt-hAMH mice was used as a model to examine the process of postnatal LC differentiation. Testis structure-function studies were performed in age-matching Mt-hAMH and C57BL/6 (controls) mice; testicular components were quantified and circulating testosterone and thyroid hormone levels (thyroxine/T4 and triiodothyronine/T3; necessary for postnatal LC differentiation) were determined. Results revealed that Mt-hAMH mice were heavier and their testis weights were smaller compared to controls. Mast cells were present in Mt-AMH testis interstitium, but absent in controls. The absolute volumes of seminiferous tubules (ST), testis interstitium, LC and blood vessels per testis were lower and lymphatic space was higher in Mt-hAMH mice than in controls (p<0.05). The average cell LC volume and their number per testis, ST length, plasma testosterone, luteinizing hormone-stimulated testosterone secretion per testis and per LC in vitro, plasma T4 and T3 were significantly lower in Mt-hAMH mice compared to controls (p<0.05). Increased body weight in Mt-hAMH mice could be attributed to the reduced T4 and T3. Reduced testis weight in Mt-AMH mice is explained by the reduced ST volume in them. Reduced plasma testosterone, testicular and LC testosterone secretion in vitro in Mt-hAMH mice can be explained by the reduced number, size and steroidogenic potential of LC in Mt-hAMH mice. Study revealed several structure-function deficiencies in Mt-AMH mouse compared to controls, which were not documented in previous investigations. As hypothyroidism causes arrest in postnatal LC differentiation, it is suggested that the reduced LC number in Mt-hAMH testes could be at least in part due to their reduced thyroid hormone levels. However, latter concept needs to be further tested in future investigations