Ultradian oscillations of plasma glucose, insulin, and C-peptide in man during continuous enteral nutrition.

The profiles of plasma glucose, insulin, and C-peptide were studied in normal men receiving continuous enteral nutrition. Large oscillations occurred with periods of 53-113 min. Their mean amplitudes, expressed as a percentage of the 24-h mean, were as high as 20% for glucose, 54% for insulin, and 56% for C-peptide. The oscillations of plasma insulin levels throughout the 24 h were concomitant with those of C-peptide. Rapid 8- to 14-min plasma insulin and glucose oscillations were smaller in magnitude and could only be detected in some segments of the longer period oscillations. These results indicate that in addition to the previously described 8- to 14-min oscillations, plasma glucose, insulin, and C-peptide oscillate at a mean 80-min periodicity in man during continuous enteral nutrition. These oscillations may reflect a pancreatic oscillatory mechanism and/or cyclic variations in gastrointestinal motility or peripheral glucose uptake.