Oscillations in insulin secretion during constant glucose infusion in normal man: relationship to changes in plasma glucose.
Peripheral plasma or serum concentrations of glucose, insulin, C-peptide, glucagon, and cortisol and insulin secretory rates (ISR) were determined at 15-min intervals in eight normal subjects during a constant iv infusion of 4.5 mg glucose/kg.min for a 24-h period. During each sampling interval, the secretory rate of insulin was calculated by deconvolution of the peripheral plasma C-peptide concentration using C-peptide kinetic parameters derived after bolus injections of C-peptide in individual subjects. Periodogram analysis of the individual glucose curves demonstrated a circadian rhythm in all subjects, with a major nocturnal acrophase occurring at an average clock time of 0228 h (range, 0045-0350 h). In five of the eight subjects, a minor acrophase occurred at an average time of 1774 h (range, 1530-2045 h). This diurnal variation in plasma glucose levels was not paralleled by a similar pattern in insulin secretion. Although glucose was infused at a constant rate, significant pulses were found in glucose, insulin, and C-peptide levels and ISR; the pulse durations of these parameters were 182 +/- 30 (+/- SE), 89 +/- 5, 100 +/- 8, and 85 +/- 5 min, respectively, and their periodicities were 208 +/- 33, 106 +/- 7, 114 +/- 10, and 106 +/- 7 min. The durations and frequencies for pulses of insulin, C-peptide, and ISR were not significantly different, whereas glucose pulses had a longer duration and were less frequent (P less than 0.05, by analysis of variance). On the average, 54 +/- 9% of the C-peptide pulses and 47 +/- 8% of the ISR pulses were concomitant with a pulse in glucose levels. Moreover, approximately half of the C-peptide and ISR pulses that were not concomitant with a glucose pulse occurred in synchrony with a shoulder on the up-stroke or down-stroke of glucose pulses. Analysis of glucagon and cortisol profiles revealed no significant associations with the insulin and glucose oscillations. In conclusion, during a constant glucose infusion in normal subjects, regular oscillations of insulin secretion occur at 80- to 120-min intervals. Their tight coupling with glucose oscillations and the lack of association with fluctuations of glucagon and cortisol suggest that these oscillations represent a dynamic property of the insulin-glucose feedback loop.
Shapiro
E T
ET
Department of Medicine, University of Chicago, Pritzker School of Medicine, Illinois 60637.
Tillil
H
H
Polonsky
K S
KS
Fang
V S
VS
Rubenstein
A H
AH
Van Cauter
E
E
D000328:Adult; D001786:Blood Glucose / Q000032:analysis*; D002096:C-Peptide / Q000008:administration & dosage / Q000097:blood / Q000493:pharmacokinetics; D002940:Circadian Rhythm; D005260:Female; D005934:Glucagon / Q000097:blood; D005947:Glucose / Q000008:administration & dosage*; D006801:Humans; D006854:Hydrocortisone / Q000097:blood; D007262:Infusions, Intravenous; D007328:Insulin / Q000097:blood / Q000378:metabolism*; D000078790:Insulin Secretion; D008297:Male; D012636:Secretory Rate
D001786:Blood Glucose; D002096:C-Peptide; D007328:Insulin; D005934:Glucagon; D005947:Glucose; D006854:Hydrocortisone