Circadian Rhythms and Episodic Hormone Secretion in Man

The temporal ordering of physiological and pathological processes has always been of considerable interest to the biological scientist as well as to the clinician. How­ ever, the historical dominance of the concept of constancy of the milieu interior and biological homeostasis as formulated by Claude Bernard in France and Walter B. Cannon in the United States has directed most past research efforts in the direction of studying stimulus-response and steady-state mechanisms. During the past 25 years, however, the field of biological rhythms has made great strides and has emphasized that all singleand multicell organisms and a wide variety of biological functions within these organisms demonstrate endogenous oscillatory behavior. The disciplines of endocrinology and neuroendocrinology have been at the forefront of these issues because of the critical interface relationsips of the central and peripheral nervous system, endocrine secretory systems, and the blood circulat­ ing communicative pathway. During the past ten years there has been a major conceptual change emphasizing the rhythmic oscillatory and episodic temporal ordering of neuroendocrine events in relation to the 24-hr sleep-waking rhythm. The cross-fertilization of the disciplines of biological rhythms, sleep physiology, and neuroendocrinology has led to a series of important observations which have chal­ lenged 24-hr homeostatic and steady-state concepts. The use of the techniques of frequent serial blood sampling, sophisticated microchemical assay techniques, and polygraphic sleep stage analysis have allowed studies to be carried out in man correlating large numbers of sequential multiple hormone measurements with sleep­ waking functional states. The results of these studies have demonstrated that hor-