The purpose of this study was to develop an animal model in which a change in the length of the day could induce a rapid alteration in pituitary gonadotropin release. The transfer of castrated male hamsters (castrated for 34 days) that had been maintained on a nonstimulatory LD 6:18 light cycle for 14 weeks to a stimulatory LD 14:10 light regime resulted in a 2–3 fold increase in serum FSH levels within three days. Furthermore, exposure to a single LD 14:10 light cycle also induced a significant increase in serum FSH titers within three days, even though the animals had been returned to LD 6:18. This animal model should prove extremely useful in elucidating the neural, endocrine and cellular events which mediate the effects of light on reproductive function.
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