Danazol Inhibits Steroidogenesis in the Rat Testisin Vitro

Abstract

The effects of danazol on steroidogenesis in vitro in the rat testis were examined by studying androgen synthesis in rat Leydig cells cultured with danazol, danazol binding to rat testis microsomal cytochrome P-450, and enzyme kinetics of danazol inhibition of the microsomal enzymes of testicular steroidogenesis. Concentrations of danazol as low as 1 .mu.M suppressed LH[luteinizing hormone]-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 .mu.M. Danazol inhibited progesterone and 17.alpha.-hydroxyprogesterone binding to microsomal P-450 with apparent spectral inhibition constants of 2.4 .mu.M and 2.8 .mu.M, respectively. Danazol competitively inhibited 3.beta.-hydroxy-.delta.5-steroid dehydrogenase-isomerase (KI = 5.8 .mu.M), 17.alpha.-hydroxylase (KI = 2.4 .mu.M), 17,20 lyase (KI = 1.9 .mu.M), and 17.beta.-hydroxysteroid dehydrogenase (KI = 4.4 .mu.M). Low concentrations of danazol apparently directly inhibit steroidogenesis in the rat testis in vitro.