Effect of starvation on the circadian adrenocortical rhythm in rats

The circadian rhythm of blood corticosterone was examined in rats whose feeding was restricted to a specific time of day. The peak of the corticosterone level was found just before feeding time regardless of whether, the rats were kept on a 12-h light, 12-h dark cycle or in constant light or were blinded. It took at least 10 days to establish the corticosterone rhythm corresponding to the feeding time, but once it had been established, it persisted for at least 2 days of stravation regardless of the lighting condition. It is concluded that the corticosterone rhythm entrained by food is endogenous.