Dynamics of steroid uptake in rat testis studied by quantitative autoradiography.

Localization of radioactive steroids in rat testis was studied by autoradiography of tissue section. For autoradiography small tissue samples were frozen, freeze-dried under vacuum, fixed with osmium vapor and embedded in epon. The transfer of radioactive steroids was studied after in vitro perfusion of radioactive steroids in the testes isolated from hypophysectomized animals, thereby excluding the interference of endogenous steroids. Quantitative autoradiography on the basis of grain densities after perfusion of testes with tritiated pregnenolone or testosterone, revealed an accumulation of the label in the Leydig cell cytoplasm. After longer perfusion periods the amount of label in the seminiferous tubules increased and a preferential localization was observed in the basal cytoplasm of Sertoli cells and in lipid droplets. Perfusion of testes with estradiol-17 beta resulted in a distinctly different pattern of radioactivity in the autoradiographs. A high labeling of the Leydig cell nuclei was observed in combination with a low general labeling of all the other cell structures. The results suggest that different steroids are localized in different specific areas of the rat testes in vivo.