RESUMO
To assess the influence of various light-dark cycles on the reproductive system of sexually immature male albino rats, 64 immature rats were included in this study. The rats were grouped into 4 equal groups: Group I: exposed to long photoperiod, Group II: exposed to short photoperiod. a Group III: exposed to complete darkness Group IV: control group exposed to natural day light. These groups were divided into 2 equal subgroups and received treatment for 1 and 3 months respectively. The rats were sacrificed following daily exposure, blood was collected, and plasma was separated and used for determination of L.H.-and testosterone by RIA. The testes were dissected, weighed and prepared for histological study. The rats exposed to long photoperiod had reached puberty earlier than the control. While those exposed to short photoperiod and complete darkness remained immature. Testicular weight and number of round spermatids had significantly increased in long photoperiod group compared with control, while those exposed to short photopericd and complete darkness group had significantly reduced testicular weight and less number of round spermatids compared with controls. LH and testosterone were significantly increased in Icng photoperiod group compared with control, short photcperiod and complete darkness group. The alterations observed in short photoperiod and complete darkness exposed rats were presumably due to inhibitory effect of melatonin on the neuroendocrine gonadal axis in those animals