Analysis of circadian rhythms in human adrenocortical secretory activity

Abstract

The major rhythms in adrenal steroid secretion appear to be related to habitual patterns of activity and are not related in any fixed way to the external environment. They exhibit distinct circadian (approximately 24-hr.) periodicity only if habitual activity patterns follow a circadian schedule. The dominant factor conferring apparent circadian rhythmicity upon aldosterone secretion is the effect of upright posture, which acts apparently by stimulating the renal production of renin. The dominant factor conferring apparent circadian rhythmicityuponACTH ([adreno corticotrophic hormone] and thereby cortisol) secretion is the sleep-wake schedule. By rescheduling postural and sleep-wake patterns, it is possible to abolish the 24-hr, periodicity of adrenal steroid secretion. The concept that there is an adrenal cycle with inherent periodicity of about 24 hrs. cannot be accepted without further reappraisal.