Abstract
Pineal serotonin N-acetyltransferase (SNAT; E.C.2.3.1.5) activity was determined 3 times/day throughout the estrous cycle in rats exposed to 6L:18D or 14L:10D lighting conditions. The magnitude of increased SNAT activity measured during the dark phase of a photoperiod did not vary significantly throughout the estrous cycle in either photoperiod examined suggesting that SNAT does not regulate changes found in pineal melatonin content during the estrous cycle.