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 C_17–20-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, C_17–20-lyase and cytochrome P₄₅₀).