A CORRELATIVE STUDY OF ENDOCRINE RHYTHMS IN RATS

Abstract

ABSTRACT Several endocrine rhythms have been studied simultaneously in the same group of rats under resting conditions. A parallel circadian periodicity was found for adrenal and plasma corticosterone, pituitary and plasma ACTH, and for the first time, for pituitary vasopressin. These rhythms are typical for nocturnal animals, demonstrating a distinct peak before the onset of darkness and lowest values at the beginning of the light period. An opposite behaviour was found for pituitary TSH in male rats showing a significant fall at the peak time of the other hormones, whereas in female rats this fluctuation was not observed. No CRF-like material could be obtained from hypothalamic tissue under resting conditions. The methods used in this study and the results obtained are discussed together with the relevant literature.