Ultradian endocrine rhythms: A multioscillatory system

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Abstract
In this study, we analyse the temporal organization within the 24‐h period of three different endocrine systems, renin‐angiotensin, insulin and glucose, ACTH and cortisol, which display similar cycles with a period of about 100 min, and examine their relationships to meal intake and to the cyclic alternation of REM‐NREM sleep. The 24‐h profiles were established simultaneously in 6 subjects who had standard meals and in 4 subjects under continuous enterai nutrition. During night‐sleep, plasma renin activity displayed sustained oscillations which were closely related to the REM‐NREM sleep cycles. No systematic relationship was found between the sleep stages and, either the small nocturnal fluctuations in insulin and glucose observed in normally eating subjects, or the sustained oscillations observed in subjects under continuous enterai nutrition. Similarly, the secretory episodes of ACTH and cortisol were not coordinated with the REM‐NREM sleep cycles. During the day‐time, meals amplified ACTH, cortisol and renin release, and thus synchronized the spontaneously occurring fluctuations. Meals also stimulated pancreatic secretion and induced two to five postprandial insulin and glucose peaks, which gave damped oscillatory patterns. No temporal concordance was found between cortisol secretory episodes, and renin or insulin oscillations. The different relationships between the hormonal oscillations and the REM‐NREM sleep cycles, as well as the different effect of meals which either modify the oscillatory patterns or initiate them, suggest that there are wide variations in the processes generating the ultradian endocrine rhythms. Their functional and adaptational significance has yet to be explored.