Effects of Melatonin and an Aqueous Pineal Extract on Adrenal Secretion of Reduced Steroid Metabolites in Female Rats

The effects of melatonin and an aqueous extract of bovine pineal glands on adrenal function were studied in pinealectomized, ovariectomized and hypophysectomized rats. Melatonin (50 microgram i.p., twice daily for 1 week) stimulates adrenal 5 alpha-reductase activity in intact animals and after ovariectomy. A corresponding enhancement in the secretion of the principal 5 alpha-reduced metabolites of corticosterone (B), dihydrocorticosterone (DHB) and tetrahydrocorticosterone (THB), occurs in vivo. As a result, proportional output of B declines. In contrast, an aqueous pineal extract (360 mg bovine pineal tissue/day for 1 week) fails to alter reductase activity or to produce the secretory changes associated with increased reductive metabolism of B. Melatonin also stimulates adrenal reductase activity in hypophysectomized rats. The results suggest that melatonin is a potential contributor to the physiologic regulation of adrenal steroidogenesis.