AGING AFFECTS DEVELOPMENT AND PERSISTENCE OF FEEDING-ASSOCIATED CIRCADIAN-RHYTHM IN RAT PLASMA-CORTICOSTERONE

Effects of aging on development and persistence of feeding-associated circadian rhythm were examined with respect to the prefeeding plasma c orticosterone peak under restricted feeding. Old (20 mo), middle-aged (12 mo), and young (2.5 mo) male rats were subjected to a restricted f eeding schedule for 21 days in which free across to food was limited t o 2 h/day in the light phase. Prefeeding corticosterone peak was detec ted 1 wk after the start of the schedule in the young and 3 wk after i n the old and middle-aged rats. After the restricted feeding, a feedin g/fasting cycle composed of 7 days of ad libitum feeding and 3 days of fasting was imposed four times. The persistence of feeding-associated rhythm was evaluated by examining the reappearance of the corticoster one peak at the previous meal time during each fasting period of the f eeding/fasting cycle. The corticosterone peak was not detected in the old and middle-aged rats even at the first cycle, but it was still dis tinct at the third cycle in the young rats. In conclusion, aging impai red the development and persistence of feeding-associated circadian rh ythm in rats.