Effects of photoperiod and temperature on the binding of follicle-stimulating hormone (FSH) to testicular preparations and plasma FSH concentration in the Djungarian hamster, Phodopus sungorus

The effects of artificial photoperiod and temperature on testicular FSH binding and plasma FSH levels were studied in adult male Djungarian hamsters. In Exp I, hamsters were transferred to long day (LD) photoperiods (16-h light, 8-h dark) after 8 weeks of adaptation in short day (SD) photoperiods (8-h light, 16-h dark), but the ambient temperature was maintained at 25 C throughout the experiments. A marked increase in the total FSH binding per two testes occurred between 10 and 47 days after transfer to LD, a change that was accompanied by testicular growth. Binding of FSH per testicular weight decreased during the same period. Scatchard plot analyses of the parameters indicated that LD decreased both the concentration of FSH binding sites and the equilibrium dissociation constant (K(d)). Plasma FSH levels increased between 10 and 47 days after transfer to LD. In contrast, when hamsters reared under LD for 12 weeks were transferred to SD (Exp II), FSH binding per unit weight basis increased 19 weeks after transfer to SD, but the total binding per two testes decreased markedly. In Exp III, sexually mature male hamsters were subjected to different ambient temperature and photoperiods. There were no significant effects of different ambient temperatures on the testicular weight and testicular FSH binding in animals exposed for 8 weeks to either LD or SD. However, plasma FSH levels of hamsters maintained at 25 C under LD was significantly higher than FSH levels at 7 C under LD. A similar effect of temperature on plasma FSH levels was observed in hamsters under SD. The present study indicates that photoperiod is a more important environmental factor than temperature for the regulation of FSH receptor in the Djungarian hamster.