Critical role of food amount for prefeeding corticosterone peak in rats.

The effects of food on plasma corticosterone levels were examined in rats under restricted daily feeding or prolonged food deprivation. High hormone levels before feeding were observed when the daily meal was restricted to 2 h at a fixed time of day, but it was not detected when food availability was extended to 6 h. The amount of food intake under the latter condition was comparable to that in 24 h of ad libitum feeding. After the termination of restricted feeding, the prefeeding hormone peak was maintained in rats fasted subsequently but disappeared when rats were returned to ad libitum feeding. Food deprivation for 10 days increased plasma corticosterone levels in the light period, resulting in abolition of the circadian rhythm. A subsequent meal decreased the hormone level such that the 24-h mean hormone level after food ingestion was inversely related to the amount of food intake. When rats were allowed to feed for 6 h after prolonged food deprivation, the prefeeding hormone peak observed at the second meal disappeared at the fourth meal. The amount of food consumption in these rats increased and reached a level comparable to that with ad libitum feeding at the third meal. It is concluded that the amount of food intake is critical for the development and maintenance of the prefeeding hormone peak under restricted feeding; prolonged fasting.