Hormonal modulation of pineal melatonin synthesis in rats and Syrian hamsters: effects of adrenalectomy and corticosteroid implants.

Pineal levels of tryptophan, 5-hydroxytryptophan, serotonin, N-acetylserotonin, melatonin, 5-hydroxyindoleacetic acid and the activities of the enzymes N-acetyltransferase and hydroxyindole-O-methyltransferase were determined in male albino rats and Syrian hamsters that were implanted with the appropriate corticosteroid or adrenalectomized two weeks earlier. Melatonin content and NAT activity were increased at 4 hours (during darkness) in adrenalectomized hamsters; conversely, no alterations in melatonin levels were observed in either adrenalectomized or implanted rats. It is suggested that the changes in adrenal function probably have a minor influence on pineal melatonin production.