Temporal difference of thyrotropin-releasing hormone in prevention of testicular regression in golden hamsters exposed to short photoperiods: possible involvement of beta-endorphin.

Male golden hamsters were exposed to long photoperiod or short photoperiod (SP) and injected with 1 microgram TRH and/or 1 microgram LHRH at lights on (LO) or lights off (LX) for a total of 8 weeks. Both TRH and LHRH prevented testicular regression if they were injected at LO. Injected at LX, TRH did not prevent testicular regression, and LHRH was only partially effective. Plasma beta-endorphin levels were significantly higher in groups with atrophic testes. These results indicate that TRH like LHRH can prevent SP-induced testicular regression in hamsters by some unknown mechanism and that beta-endorphin may be involved in the control of testicular function in hamsters.