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Biology of Reproduction, Vol 13, 475-481, Copyright © 1975 by Society for the Study of Reproduction
1 Department of Zoology, The University of Texas at Austin,
Austin, Texas 78712 Male golden hamsters were exposed to nonstimulatory short days for 25 weeks, and the effects
on gonadal weight and serum gonadotropin levels were assayed at biweekly intervals. Within 11
weeks after animals were transferred from a photostimulatory (LD 14:10) to a nonstimulatory (LD
6:18) light cycle, serum LH and FSH titers, as well as testicular weight had decreased markedly (4-,
5- and 13-fold, respectively). Continued exposure to LD 6:18 resulted in gradual increases in serum
gonadotropin levels and subsequently in the complete recrudescence (regrowth) of the testes by 25
weeks. The testis itself does not appear to be involved in the "spontaneous" increase in serum
gonadotropin levels since these levels also increased gradually in hamsters that were castrated after
10 weeks of LD 6:18 and then were exposed to LD 6:18 for an additional 17 weeks. The observation of a gradual increase in the activity of the neuroendocrine-testicular axis during
prolonged exposure to LD 6:18 suggested to us that the hamster’s reproductive system might
become more responsive to photostimulation with increasing length of prior exposure to
nonstimulatory photoperiods. To examine this possibility hamsters maintained on LD 6:18 for
either 10 or 13.5 weeks were transferred to LD 16:8 for 3.5 weeks, and then sacrificed. In those
hamsters exposed to nonstimulatory photoperiods for 13.5 weeks there was a greater increase in
testicular size after photostimulation (5.5-fold increase) than in those animals exposed for only 10
weeks (2.2-fold increase). A similar pattern was observed in serum gonadotropin levels, indicating
that the neuroendocrine-gonadal axis of the male hamster increases in sensitivity to photostimulation with a longer exposure to nonstimulatory photoperiods.
Accepted on August 6, 1975
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