Evidence for mutually antagonistic actions of thyroid releasing hormone and inhibin at pituitary-gonadal-prostate-spermatozoal axis

In-vivo as well as in-vitro studies carried out demonstrate for the first time the interaction between thyroid releasing hormone (TRH) and inhibin at the pituitary, testes, prostate and spermatozoa levels. At the pituitary level both peptides act as antagonists to each other and modify the release of pituitary hormones. Further, these peptides act at the prostatic level wherein they modulate ornithine decarboxylase activity as well as 5 α-reductase activity. At the testicular level TRH blocks inhibin biosynthesis whereas in semen, it significantly reduces the binding of spermatozoa to specific antibodies directed against inhibin. In conclusion, although TRH and inhibin are widely different in their molecular size and chemical structure, these peptides seems to act antagonistically at multiple sites.