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 corticosterone peak under restricted feeding. Old (20 mo), middle-aged (12 mo), and young (2.5 mo) male rats were subjected to a restricted feeding schedule for 21 days in which free access to food was limited to 2 h/day in the light phase. Prefeeding corticosterone peak was detected 1 wk after the start of the schedule in the young and 3 wk after in the old and middle-aged rats. After the restricted feeding, a feeding/ 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 corticosterone peak at the previous meal time during each fasting period of the feeding/fasting cycle. The corticosterone peak was not detected in the old and middle-aged rats even at the first cycle, but it was still distinct at the third cycle in the young rats. In conclusion, aging impaired the development and persistence of feeding-associated circadian rhythm in rats.