Endocrinology, Vol 101, 1676-1682, Copyright © 1977 by Endocrine Society

ARTICLES

Danazol inhibits steroidogenesis in the rat testis in vitro

RL Barbieri, JA Canick and KJ Ryan

The effects of danazol on steroidogenesis in vitro in the rat testis were examined by studying: 1) androgen synthesis in rat Leydig cells cultured with danazol, 2) danazol binding to rat testis microsomal cytochrome P-450, and 3) enzyme kinetics of danazol inhibition of the microsomal enzymes of testicular steroidogenesis. Concentrations of danazol as low as 1 micrometer suppressed LH-stimulated testosterone and androstenedione production in cultured Leydig cells. The addition of danazol to a preparation of testicular microsomes elicited a type I cytochrome P-450 binding spectrum, with an apparent spectral dissociation constant (Ks) of 4.8 micrometer. Danazol inhibited progesterone and 17alpha-hydroxy-progesterone binding to microsomal P- 450 with apparent spectral inhibition constants of 2.4 micrometer and 2.8 micrometer, respectively. Danazol competitively inhibited 3beta- hydroxy-delta5-steroid dehydrogenase-isomerase (apparent enzymatic inhibition constant, KI = 5.8 micrometer), 17alpha-hydroxylase (KI = 2.4 micrometer), 17,20 lyase (KI = 1.9 micrometer), and 17beta- hydroxysteroid dehydrogenase (KI = 4.4 micrometer). These findings indicate that low concentrations of danazol directly inhibit steroidogenesis in the rat testis in vitro.