RU-486 inhibits rat gonadal steroidogenesis.

RU-486 is a synthetic steroid analogue that can inhibit adrenal steroid synthesis in the rat and rhesus monkey. We measured the activities of five testicular and two ovarian microsomal steroidogenic enzymes to assess the potential effect of RU-486 on rat gonadal steroidogenesis. Hypophysectomized, gonadotropin-replaced rats received RU-486 or a vehicle solution twice daily for seven days. The animals were sacrificed and their gonads were resected, weighed, and microsomal enzyme activities were measured according to RU-486 treatment. Testicular 17-hydroxylase and aromatase activity decreased in RU-486 treated animals whereas 17,20-desmolase, 3 beta-hydroxysteroid dehydrogenase and 17-ketosteroid reductase activities were unaffected. Ovarian 17-hydroxylase but not 3 beta-hydroxysteroid dehydrogenase activity was decreased in the animals receiving the drug. We conclude that RU-486 inhibits both testicular and ovarian steroidogenesis in the rat.