Ex vivo studies on the acute and chronic effects of DHEA and DHEA-sulfate on melatonin synthesis in young- and old-rat pineal glands

Abstract

This study investigates the effects of acute and chronic injections of the neurosteroid dehydroepiandrosterone (DHEA) and its sulfate DHEA-S on pineal gland melatonin synthesis. Pineal melatonin production and plasma melatonin levels were investigated in young (9-week-old) and old (27-month-old) male Wistar rats. DHEA or DHEA-S have been administered acutely in a single intraperitoneal injection at a dosage of 50, 250, or 500 μg per animal, or on a long-term basis, i.e., for 8 days at a dosage of 100 μg per animal, 1 h before the onset of darkness. DHEA, at a dose of 50, 250, or 500 μg per animal, administered acutely to rats had no significant effects on pineal melatonin production whatever the age of the animals. In contrast, 500 μg DHEA-S induced a significant increase in the pineal melatonin content (15% in young animals and 35% in old animals) and the activity of N-acetyltransferase, the rate-limiting enzyme for melatonin synthesis in the pineal gland, (40% in young animals and 20% in old animals), whithout altering the activity of hydroxyindole- O-methyltransferase whatever the age of the animals. At lower concentrations (50 or 250 μg) DHEA-S had no effect on pineal melatonin production regardless of the age of the rats. Chronic injection of DHEA or DHEA-S at a dose of 100 μg had no effect on pineal melatonin or NAT and HIOMT activities in the two age groups. This work shows that DHEA-S (and not DHEA) is able, at pharmacological concentrations, to stimulate melatonin production by rat pineal glands regardless of the age of the animals.