Effects of short-term treatment with testosterone on the secretion of FSH and LH in castrated golden hamsters exposed to short days

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Abstract
Castrated hamsters which were transferred from long (14L: 10D [h of light: h of dark]) to short (9L: 15D) days and received testosterone-filled capsules for 1 wk after transfer failed to show a significant suppression in the plasma levels of FSH and luteinizing hormone after capsule removal. In contrast, gonadotropin concentrations were suppressed in hamster in which the long-day castration response had been blocked with exogenous testosterone. After castration on long days and exposure to 10 wk of short days pituitary gland weight and gonadotropin content, as well as plasma FSH titers, were higher in control animals than in those that had received testosterone implants for 7 wk of short days. Failure of castrated hamsters to respond to the suppressive effects of short days apparently reflects castration-induced changes in hypothalamo-pituitary physiology rather than a neuroendocrine mechanism by which photoperiod modulates gonadotropin secretion.