Effect of Melatonin on Photic-Independent and Photic-Dependent Testicular Growth in Juvenile and Adult Male Golden Hamsters1

Four-week-old male hamsters were implanted with either empty or melatonin filled Silastic capsules that totaled 100 mm in length. The animals were maintained on either LD 6:18 or LD 14:10, and testicular development was monitored until the animals were 10 weeks old. Testicular development was not influenced by either the photoperiod or melatonin treatment and at 10 weeks of age the testes of all the animals had reached a size comparable to that observed in sexually mature animals. Exposure of hamsters to LD 6:18 beyond 10 weeks of age resulted in complete testicular regression. In contrast to juvenile hamsters, testicular growth was suppressed by melatonin treatment in adult hamsters transferred from a nonstimulatory LD 6:18 light cycle to a stimulatory LD 14:10 photoperiod. These results suggest that melatonin treatment via hormone filled Silastic capsules does not influence photic-independent testicular growth, but does influence photic-dependent testicular recrudescence.