Reduced pineal and plasma melatonin levels and gonadal atrophy in old hamsters kept under winter photoperiods

Abstract

Young (3-month-old) and old (20-month-old) male Syrian hamsters were kept under natural photoperiodic and temperature conditions from Nov. & to Jan 9. Groups of animals were killed at either 1600 h (during the day) or at 0400 (during the night). In young hamsters, night time levels of pineal melatonin were increased 11-fold over those measured during the day. Conversely, in the old hamsters pineal melatonin levels at night were not statistically significantly elevated over those measured during the day. During both the day and night the pineal glands of old hamsters contained less melatonin than did those of the young animals (p<0.01 and p<0.001, respectively). Young animals exhibited a nocturnal increase in plasma melatonin titers; however, in the old hamsters no night time rise in plasma melatonin concentration could be documented. As in the pineal gland, plasma levels of melatonin were lower in the old hamsters during both the day and night. In both young and old hamsters the short days of the winter were associated with atrophy of the testes and accessory organs. The degree of regression of these organs seemed to be somewhat greater in the young animals than that in the old hamsters.