Effect of calcium on melatonin secretion in chick pineal gland I.

Melatonin is the neurohormone which is synthesized by the pineal gland and secreted rhythmically. The role of calcium in the activation of melatonin production remains unknown. In this study, we demonstrated that calcium input participates in the regulation of chick pineal gland. Pineal glands from Gallus domesticus were perifuse with Krebs medium (controls) or with Krebs medium plus drugs (ethylene glycol tetraacetic acid (EGTA) or calcium ionophore A23187). When EGTA was added to the perifusion medium, free extracellular calcium concentrations were dramatically decreased and melatonin synthesis was decreased. On the other hand, when the calcium ionophore A23187 was added to the perifusion medium, chick pineal glands exhibited a marked increase in secretion of melatonin. No effects were observed when chick pineal glands were treated with drugs during or after the time of the natural peak levels. We propose that calcium input from extracellular medium and output from intracellular calcium reserves are primary mechanisms in the activation of melatonin synthesis in the chick pineal gland.