Abstract
SummaryPineal 5-hydroxytryptamine (5-HT) and hydroxyindole-O-methyl transferase (HIOMT) activity were measured in adult rhesus macaques killed at 6 times during daily periods with a standard photoperiod (6:00 AM to 5:00 PM). Pineal 5-HT increased during the daily light period to a peak of 83.8 ng/mg (Se = 8.4) just before the daily period of darkness, at which time it fell to about one-fourth of its peak level. HIOMT activity was greatest at night and was significantly lower during the daily light period. Comparisons of these rhythms in the macaque with those of rat and pigeon suggest the desirability of studies of pineal darkness-dependent responses and activities in primates.
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