Immunocytochemical and biochemical studies on the localization and changes of 17 α-hydroxylase/C17–C20 lyase activity in immature rat ovary treated with PMSG and hCG

Summary

The localization of cytochrome P-450 of 17 α-hydroxylase/C17–C20 lyase (P-450_{17 α, lyase}) and the changes of the enzyme activity were studied immunocytochemically and biochemically in the ovaries of immature rats treated with PMSG (pregnant mare serum gonadotropin) and hCG (human chorionic gonadotropin). Immunocytochemically, P-450_{17 α, lyase} was localized in both the theca interna cells and interstitial gland cells of the ovaries of immature rats treated with PMSG for 48 h. After hCG administration, the immunoreactive cells rapidly decreased in number in the PMSG-pretreated rat ovary. Namely, 6 h after the hCG injection, positive staining for P-450_{17 α, lyase} was recognized only in a few theca interna cells, while 12 h after the injection to immunostained cells were detected in the ovary. Forty-eight hours after the hGC treatment (96 h after the PMSG injection), most of the theca interna cells and the interstitial gland cells became immunopositive for P-450_{17 α, lyase} again. The 17 α-hydroxylating activity of P-450_{17 α, lyase} was 0.5, 0.22 and 0.03 nmol/min/mg protein in the ovarian microsomes of PMSG-treated, PMSG+hCG(3 h)-treated and PMSG+hCG(6 h)-treated rats, respectively. Changes of the hydroxylase activities in all the experimental groups are almost parallel to those of P-450 contents in the microsomes. These immunocytochemical and biochemical findings suggest that 1) P-450_{17 α, lyase} is localized in both the theca interna cell and interstitial gland cell, and these cells are the main site of the androstenedione production in the ovary, and that 2) the decreased production of estrogen occurring just before ovulation is not brought about by the decreased activity of P-450_{17 α, lyase}, but done by the loss of the enzyme.