Evidence for a circadian rhythm of insulin secretion.
Boden, Guenther, Jose Ruiz, Jean-Luc Urbain, and Xinhua Chen.
Departments of Medicine (GB, JR, XC) and Diagnostic Imaging (JLU)
and the General Clinical Research Center, Temple University Schools
of Medicine, Philadelphia, PA 19140
APStracts 3:0074E, 1996.
Insulin secretion was studied in healthy volunteers at 3 different
levels of glycemia. Plasma glucose was clamped at 5, 8.8 and 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 3 glucose
concentrations tested but were most clearly seen at 12.6 mM. ISR and
serum insulin concentration changed in a circadian ( 24 h) rhythm,
increasing from a nadir at between midnight and 6 AM and reaching a
peak between noon and 6 PM. 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 superior in the morning than at night.
Received 2 October 1995; accepted in final form 19 March 1996.
APS Manuscript Number E482-5.
Article publication pending Am. J. Physiol. (Endocrinol. Metab.).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 16 April 96