A specific action of estradiol on enzymes involved in testicular steroidogenesis

Abstract

LH-Stimulated steroid production was studied in vitro in Leydig cells isolated from testes of 26, 32, 44, 54 and 64-day-old rats treated with estradiol implants. Five days after implantation of estradiol, the maximal testosterone production was decreased in 32, 44, 52, and 64-day-old rats, while maximal Δ5-pregnenolone production was not changed. In 26-day-old rats, however, production rates of both testosterone and Δ5-pregnenolone were decreased. The estradiol effect on testosterone production could be observed 48 h after implantation. Testosterone treatment for 5 days resulted in decreased testosterone as well as Δ5-pregnenolone production. Corticosterone implants were without effect. In contrast to the decrease in the maximal response with respect to testosterone production after estradiol treatment, a fivefold increase was observed in the sensitivity of Leydig cells for LH with respect to Δ5-pregnenolone and testosterone production. Administration of estradiol to 32-day-old rats resulted in decreased testicular levels of microsomal cytochrome P450 and in the formation of 3α-hydroxy-5α-pregnan-20-one. In Leydig cells from hypophysectomized 64-day-old rats treated for 5 days with estradiol, a decrease in C17-20-lyase and 17α-hydroxylase activity was found. It is concluded that the observed decrease in testosterone production by Leydig cells from rats treated in vivo with estradiol is the consequence of a specific action of estradiol on testicular microsomal enzymes (including 17α-hydroxylase, C17-20-lyase and cytochrome P450).