Spontaneous testicular recrudescence of Syrian hamsters: role of stimulatory photoperiods.

The gonads of hamsters maintained in short photoperiods first undergo regression and then spontaneous recrudescence. The latter is indicative of refractoriness of the neuroendocrine axis to short day lengths. We tested the hypothesis that the absence of long-day stimulation contributes to the development of refractoriness to short photoperiods. Male Syrian hamsters were maintained for 26 weeks in a short-day photoperiod (8 hr light/day). Testicular regression was confirmed in all animals at week 10; thereafter different groups of hamsters were stimulated with one long day (16 hr light) every 10, 15, 20 or 30 days until week 26. Control groups were maintained continuously in long or short photoperiods, respectively. The rate of gonadal recrudescence of short-day hamsters was not affected by intermittent stimulation with long photoperiods. After 26 weeks, testes in all short-day groups had undergone recrudescence. Refractoriness to short day lengths is not counteracted by long photoperiods. The role of the pineal gland in the development of refractoriness is considered.