The overall objectives of this project are to clarify further the hormonal regulation and intra-testicular site or sites of estrogen and androgen synthesis by mammalian testes. Studies are planned or are in progress to determine: 1) the intra-testicular site of estrogen formation in rat testes and whether the site of estrogen formation by rat testes is age-dependent; and 2) the in vitro and in vivo effects of purified gonadotropins, growth hormone, and prolactin on estrogen formation and metabolism by intact testes, isolated seminiferous tubules and isolated interstitial tissue. Our recent experiments have demonstrated that the interstitial tissue is the major site of estrogen formation in human testes. The factors which regulate estrogen formation throughout development remain unknown. In view of the recent demonstration of estrogen receptors and interstitial tissue and the possible regulatory effect of 17 beta-estradiol on 17 oxidoreductase activity of interstitial tissue, further studies are planned to determine the intratesticular role of estrodiol. BIBLIOGRAPHIC REFERENCES: Payne, A.H., and R.P. Kelch, Comparison of Steroid Metabolism in Testicular Compartments of Human and Rat Testes, in Hormonal Regulation of Spermatogenesis, eds. F.S. French, V. Hansson, E.M. Ritzen, and S.N. Nayfeh, Plenum Publishing Corp., New York, N.Y., 1975, pp. 97-108. Payne, A.H., R.P. Kelch, S.S. Musich, and M.E. Halpern, Intratesticular Site of Aromatization in the Human, J. Clin. Endocrinol. (In press - June, 1976.