Abstract
The photoperiodic and hormonal regulation of melatonin-synthesizing enzymes was determined in pineals of Coturnix quail. N-Acetyl transferase (NAT) and hydroxyindole-O-methyl transferase (HIOMT) were twofold higher in pineals of female and male Coturnix quail during exposure to darkness (16L:8D). Castration decreased pineal HIOMT activity in both female and male Coturnix, while selective gonadal steroids restored activity. NAT was not affected by castration or gonadal steroids. Implantation of melatonin into female Coturnix decreased both HIOMT and NAT activities. These results suggest that NAT is regulated primarily by photoperiodicity, while HIOMT activity is a consequence of the external perceptive environment and the internal hormonal milieu, with both enzymic activities modulated by the feedback inhibitory influence of endogenous melatonin.
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