Failure of Inbreeding to Influence Pineal-Induced Gonadal Regression in Short Day Exposed Hamsters1

The rate of testicular degeneration and the drop in plasma testosterone levels were compared in what were referred to a5 short-term domesticated (STD) and long-term domesticated (LTD) Syrian hamsters when they were maintained under short photoperiodic conditions (1ight:dark cycles of 10:14). STD hamsters were derived from wild stock captured in 1971; LTD animals were derived from the original stock captured in 1930. The rate of testicular degeneration as well as the fall in plasma testosterone levels were similar in both groups of animals. After 26 weeks exposure to short days, the testes and accessory sex organs regenerated to the fully mature state in both the STD and LTD animals; likewise, plasma testosterone levels had returned to normal in both groups. Pineal melatonin levels of STD and LTD female hamsters were compared during both the light phase (2000 and 0800hr) and dark phase (0200 and 0400hr) of the daily 1ight:dark cycle. These animals were kept under photoperiodic conditions of 14: 10 with lights on daily from 0600-2000hr. Day- and night-time levels of pineal melatonin were similar in both groups of hamsters. The results indicate that inbreeding does not influence the atrophic response of the reproductive organs of male hamsters to short day exposure or the ability of the pineal gland to produce melatonin.