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Failure to Detect the "Dawn Phenomenon" in Nondiabetic Subjects with Markedly Different Patterns of Nocturnal Growth Hormone Secretion^*

Departments of Pediatrics, Divisions of Endocrinology and Metabolism and Clinical Pharmacology, and the Diabetes Research and Teaching Center, Universty of Virginia Medical Center Charlottesville, Virginia 22908

Address requests for reprints to: Dr. William L. Clarke, Division of Endocrinology and Metabolism, Department of Pediatrics, Box 386, University of Virginia, Charlottesville, Virginia 22908.

Overnight serum insulin and plasma glucose concentrations were measured every 20 min from midnight to 0900 h in 13 nondiabetic subjects. Seven were normal men, and 6 had isolated GH deficiency. The prebreakfast increase in serum insulin concentrations ("dawn phenomenon") did not occur in either group of individuals, and a progressive decline in serum insulin concentrations occurred particularly in the dawn hours (0600–0900 h). The GH secretory patterns were strikingly different in the two groups, with normal spontaneous GH peaks mostly between 0100–0200 h in the normal subjects vs. virtually flat GH secretion in the isolated GH deficiency group. The absence of the dawn phenomenon in these nondiabetic subjects regardless of their GH secretory pattern suggests that the dawn phenomenon, as described in insulin-dependent diabetic patients, is not an exaggeration of normal circadian rhythmicity in insulin sensitivity.

^* This work was supported in part by NIH Grants AM-22125 and RR-00847.

Received September 30, 1985.

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