Changes in serum immunoreactive inhibin-α during photoperiod-induced testicular regression and recrudescence in the golden hamster

Serum immunoreactive inhibin-α (irIα), FSH, LH, and testosterone (T) were measured in male golden hamsters during short-day-induced testicular regression and during testicular recrudescence following the transfer from short to long days. Serum FSH levels were maximally suppressed within 2 wk of transfer to short days. In contrast to FSH, irIα levels were not fully reduced until after 6 wk of exposure to short days, closely paralleling the timing of testicular regression. LH and T levels were also reduced within two 2k, with maximal suppression observed between 6 and 8 wk. Conversely, when males with regressed testes were transferred to long days, serum FSH rose to peak (25 ng/ml) levels by 3 wk and then declined to usual long-day levels. In contrast, serum irIα levels rose gradually, reaching adult long-day levels following 10 wk of exposure. Serum LH and T levels rose to peak levels between 5 and 8 wk before declining to adult levels. FSH, LH, and irIα levels were also measured after castration in male hamsters maintained on long or short days. Twenty-four hours after castration, levels of irIα were reduced in long-day males to levels comparable to those observed in castrated short-day males. Serum irIα levels respond slowly to abrupt changes in FSH levels after transfer to either long or short days, suggesting that testicular irIα secretion may not be directly and immediately influenced by circulating FSH levels in the hamster. Taken together, these results demonstrate that gradual changes in serum irIα occur during photoperiod- induced changes in gonadal activity and that these changes are associated with gonadal function.