Thyroid hormone and anti-Mullerian hormone (AMH) on Leydig cell differentiation: studies using C57BL/6 mice and AMH over expressing mice.

Although the thyroid hormone has stimulatory effects and anti-Mullerian hormone (AMH) has inhibitory effects on prepubertal Leydig cell (LC) differentiation, it is important to find out whether the stimulatory effect of thyroid hormone could overcome the inhibitory effect of AMH on postnatal LC differentiation. Therefore, the objective of the present study was to use the anti-Mullerian hormone overexpressing mouse (AMH++) model to understand the simultaneous effects of AMH and thyroid hormone on postnatal LC differentiation, proliferation, maturation and function and to test whether the inhibitory effect of AMH could be overcome by the stimulatory effect of the thyroid hormone. Four age groups (7, 21, 40, 90 days) of control (C57BL/6; C) and AMH++ were used. Mice received either saline or triiodothyronine (T3) SC injections daily from birth to 21days. The four experimental groups were C, C+T3, AMH++ and AMH+T3. Body and testis weights of both C+T3 and AMH+T3 mice were significantly reduced at days 21, 40 and 90, compared to their age-matched saline-treated mice (C and AMH++). BrdU studies revealed the absence of LC proliferation in AMH++ mice at day7, however, same-aged mice of C+T3 and AMH+T3 mice showed increased LC proliferation; the rate was highest in C+T3 at day21. C+T3 mice of day 21 had more LC than C mice as well as AMH+T3 and AMH++ mice. At days 40 and 90, LC number/testis in C+T3 was lower than C, however, AMH+T3 had higher LC numbers than AMH++ mice. Cellular apoptosis was not seen as the cause of reduced LC numbers. Serum testosterone was not different among groups at day 21, but significantly higher levels were seen in AMH+T3 compared to AMH++ mice at days 40 and 90. Similar pattern was seen for luteinizing hormone (LH)-stimulated testicular testosterone and androstenedione production in vitro. Findings suggest that T3-treatment for the first postnatal 21 days was able to partially counteract the inhibitory effect of AMH on prepubertal LC differentiation. Whether continuation of the T3-treatment beyond 21 days would have resulted in complete removal of this inhibition, is a question that needs to be addressed.