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Biology of Reproduction, Vol 24, 551-556, Copyright © 1981 by Society for the Study of Reproduction
Í VAN
EK 2
1 Max-Planck-Institut für Verhaltensphysiologie, D-8131 Andrechs,
Federal Republic of Germany The proposition that the temporal pattern of pineal melatonin formation and release may serve
as a transducer of photic into humoral stimuli was tested. Adult male Djungarian hamsters were
maintained for 3-4 weeks under 16L:8D, 8L:16D, and 8L:16D with additional 1 min light in the
middle of the dark period. Pineal N-acetyltransferase activity was estimated at different daytimes
as an indicator of melatonin synthesis. The pattern of the rhythms in N-acetyltransferase was
similar under 16L:8D and 8L:16D + 1 min light and dissimilar to the pattern under 8L:16D. The
high nocturnal N-acetyltransferase activity lasted for
2 Institute of Physiology, Czechoslovak Academy of Sciences,
142-20 Prague, Czechoslovakia
5 h under 16L:8D, 6 h under 8L:16D + 1
min light, and 12 h under 8L:16D. The demonstration that the regimens 16L:8D and 8L:16D + 1
min light lead to similar rhythms in N-acetyltransferase and hence in melatonin formation, together
with our previous finding that the same regimen (8L:16D + 1 min light in the middle of the dark
period) mimics the effect of long photoperiods on gonadal development and body weight, further
supports the hypothesis that the changing rhythmic pattern of melatonin formation may be
involved in conveying the photoperiodic effects.
Note:
ACKNOWLEDGMENTS
This investigation was supported by the Deutsche
Forschungsgemeinschaft, SPP "Mechanismen biologischer Uhren" and by the Czechoslovak Academy of
Sciences. The skillful technical assistance of Mrs. Marie
Svobodavá is greatly appreciated. Mrs. S. Nieschlag
greatly improved the style.
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