EFFECT OF SEASON AND PHOTOPERIOD ON THE FOLLICLE-STIMULATING-HORMONE RECEPTORS IN A SUBTROPICAL BIRD

Annual changes in and photoperiodic influence oh the weight of gonads, a parameter of gonadal activity, are much smaller in female birds tha n in males. Effect of season and photoperiod on the follicle-stimulati on, hormone receptors in the testis or ovary was studied using a subtr opical weaver finch. The number of follicle-stimulating hormone bindin g sites per unit testicular weight showed a peak in the non-breeding p hase; while the total number of binding sites per two testes was maxim al in the breeding phase and minimal in the regressive phase. In contr ast, seasonal changes in follicle-stimulating hormone binding sites in the ovary were less marked. Exposure to short-day during the breeding phase induced marked decreases in the numbers of binding sites per un it testicular weight and per two testes. These numbers markedly increa sed after transfer to long-day during the non-breeding phase. However, there was no significant effect of short-day or long-day exposure on follicle-stimulating hormone binding sites in the ovary. These results suggest that photoperiod is an effective environmental factor in the regulation of follicle-stimulating hormone receptors in the testis and the effect is manifested by pronounced changes in the testicular weig ht during annual breeding cycle.