Biol Reprod Keystone Symposia Conference on Frontiers in Reproductive Biology & Regulation of Fertility.
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Biology of Reproduction, Vol 21, 385-391, Copyright © 1979 by Society for the Study of Reproduction

Pineal Serotonin N-Acetyltransferase Activity in the Rat During the Estrous Cycle and in Response to Light

B. D. SHIVERS 1, and J. M. YOCHIM 1

1 Department of Physiology and Cell Biology, University of Kansas, Lawrence, Kansas 66045


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.

In a second experiment, SNAT activity was determined 6 times/day in rats exposed to lighting conditions of continuous darkness (DD), 2L:22D, 6L:18D, 14L:10D, 20L:4D or continuous light (LL). Although no alterations in SNAT activity were measured in LL, SNAT activity was elevated for sim8 h during the dark phase of the photoperiod throughout a broad range of other lighting conditions. Peaks in SNAT activity showed a parabolic relationship to increasing proportions of light/day and were related as well to the midpoint of the dark phase of each photoperiod. If SNAT activity is an index of melatonin production and release, these findings do not support a proposal that melatonin levels provide the rat with a measure of the duration of darkness. Instead, the results suggest that melatonin may act as an internal synchronizer cuing the animal to the midpoint of the dark phase of a photoperiod.

Note:
ACKNOWLEDGMENTS A preliminary report of these studies was presented at the Seventh Annual Meeting of the Society for the Study of Reproduction, 1974, Abstr. 120.

Submitted on December 22, 1978
Accepted on May 4, 1979






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Copyright © 1979 by the Society for the Study of Reproduction.