Melatonin Inhibition of Pineal Enzymes in Coturnix Quail

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Abstract
The activities of the melatonin-forming enzymes hydroxyindole-O-methyl transferase (HIOMT) and N-acetyl transferase (NAT) were determined in pineals of mature female Coturnix quail receiving implants of melatonin (10 mug, 1 mug, 0.1 mug) weekly for 4 weeks. Both HIOMT and NAT were significantly decreased by implants of 10 and 1 mug melatonin compared to vehicle and intact controls. Oviductal weights tended to be higher with increasing quantities of melatonin. These results suggest that melatonin exerts a feedback inhibition upon its synthesizing enzymes which may be of particular importance during the rapid sexual maturation of this species.