Abstract

In this review, attempts were made to clarify the role of feeding behavior in modifying the basal 24-h pattern of plasma corticosterone in freely moving rats. An ethosecretogram, consisting of locomotor activity and plasma corticosterone levels in conscious rats over a period of several hours, was constructed. By analyzing the ethosecretogram, it was found that the feeding effectively induced an elevation of plasma corticosterone. Conscious rats were then exposed to various kinds of feeding regimens, emphasis being laid on the effect of restricted daily feeding on the circadian skeleton of plasma hormone rhythm. We found that feeding has a bidirectional effect on hormone level along with an initiation of an interval timer mechanism which in turn uniquely modify the basal pattern of circadian hormone rhythm, especially when a pre-feeding hormone peak is formed under restricted daily feeding schedules. Furthermore, it was shown that the pre-feeding hormone peak persisted after the termination of restricted feeding and free-ran in parallel with the circadian hormone peak. It is concluded that the pre-feeding hormone peak is driven by a damped oscillator which is entrainable to restricted feeding. It is most likely that this damped oscillator is loosely driven by the circadian oscillator which is not entrainable to restricted feeding.