Short-Day Exposure Eliminates the LH Response to Naloxone in Golden Hamsters

Abstract
Short-day-induced testicular regression in golden hamsters is accompanied by changes in opiatergic control of LH release. Serum LH in long-day-exposed hamsters is elevated by subcutaneous injections of naloxone. By day 42 of short-day exposure, naloxone is unable to stimulate LH secretion; responsiveness to naloxone is restored after reexposure to long days. The change in response to naloxone may reflect a loss of opiate regulation of LH release; an alternative, but not mutually exclusive, hypothesis is that additional opiate-independent mechanisms inhibit LH despite the blockade of opiate LH inhibition by naloxone.

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