Inhibition of rat testicular heme synthesis and depression of microsomal cytochrome P-450 by estradiol benzoate.

Twenty-four hours after a single dose (50 microgram, s.c.) of estradiol benzoate (EB), rat testicular microsomal heme and cytochrome P-450 were decreased to 72 and 76% of control levels respectively. Treatment of rats with human chorionic gonadotropin (hCG) resulted in elevated levels of microsomal heme and cytochrome P-450 and increased activity of delta-aminolevulinic acid (ALA) synthase (EC 2.3.1.37). However, the hCG-mediated elevations of testicular microsomal heme and cytochrome P-450 content failed to occur in animals treated with EB. To investigate the possibility that the observed effect of EB was mediated through the pituitary, studies were conducted with hypophysectomized animals. The increased microsomal heme and cytochrome P-450 content mediated by hCG in hypophysectomized animals was again prevented by administration of EB. The elevated activity of testicular mitochondrial ALA synthase produced by hCG in both intact and hypophysectomized animals was not affected by EB. Incorporation of [14C]ALA into microsomal heme was depressed 60% 12 hr following a single dose of EB (50 microgram, s.c.). These data suggest that EB depresses testicular microsomal heme and cytochrome P-450 content by inhibiting the synthesis of heme at an enzymatic reaction other than ALA synthase.