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Am J Physiol Endocrinol Metab 271: E246-E252, 1996;
0193-1849/96 $5.00
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AJP - Endocrinology and Metabolism, Vol 271, Issue 2 E246-E252, Copyright © 1996 by American Physiological Society

ARTICLES

Evidence for a circadian rhythm of insulin secretion

G. Boden, J. Ruiz, J. L. Urbain and X. Chen
Department of Medicine, Temple University School of Medicine, Philadelphia, Pennsylvania 19140, USA.

Insulin secretion was studied in healthy volunteers at three different levels of glycemia. Plasma glucose was clamped at approximately 5, approximately 8.8 and approximately 12.6 mM for 68 h. Measured were serum insulin concentration and insulin secretion rates (ISR), the latter by deconvolution of plasma C-peptide concentration. Rhythmic patterns of ISR were identified (with a refined first-order Fourier transform) at all three glucose concentrations tested but were most clearly seen at 12.6 mM. ISR and serum insulin concentration changed in a circadian (approximately 24 h) rhythm, increasing from a nadir between midnight and 6 A.M. and reaching a peak between noon and 6 P.M. At 12.6 mM hyperglycemia, the amplitude of the insulin concentration cycles was greater than that of the ISR cycles (+/- 13.0 vs. +/- 8.7%) due to a decrease in insulin clearance (from 1.55 to 0.5 l/min, P < 0.01). Plasma melatonin levels (a marker of light-dark rhythmicity) changed in the opposite direction, i.e., they peaked when ISR bottomed and bottomed when ISR peaked. We concluded that normal human subjects have a circadian rhythm of insulin secretion, which becomes more apparent with rising ISR, and that circadian changes in ISR, rising during the day and falling during the night, may be one explanation for the well-established observation that glucose tolerance and insulin responses to glucose and meals are higher in the morning than at night.


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C. Simon, L. Weibel, and G. Brandenberger
Twenty-four-hour rhythms of plasma glucose and insulin secretion rate in regular night workers
Am J Physiol Endocrinol Metab, March 1, 2000; 278(3): E413 - E420.
[Abstract] [Full Text] [PDF]


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