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The Introduction of sensitive radioimmunological techniques for the determination of human growth hormone (GH) (1,2) has made it possible to study its concentration in plasma under various physiological and pathological conditions. Secretion of GH has been shown to respond to different stimuli, e.g., hypoglycemia (3), infusion of certain amino acids (4) and physical activity (5), but the relative importance of these factors for the release of hormone under physiological conditions has not yet been fully established. Considerable variations in the hormone level of an individual have been observed when repeated determinations were done on a single day. This and the occasional finding of unexpectedly high concentrations after an overnight fast have complicated our understanding of the normal regulation of GH concentration in plasma. Very little is known about the physiological variations of GH release during a 24-hour period. We report determinations of GH during a 24-hour fast in normal adults. These studies show a pattern of intermittent bursts of GH secretion during the night and a part of the day, with concentrations varying from undetectable to very high values. Some of the implications of this finding are discussed.
QUABBE et al. (1966) studied this question.