Slow oscillations of plasma glucose and insulin secretion rate are amplified during sleep in humans under continuous enteral nutrition

Abstract

Concomitant oscillations of plasma glucose and insulin secretion rate with a periodicity of about 80 minutes have been identified in normal humans. To determine whether these slow oscillations are influenced by sleep, peripheral levels of glucose and C-peptide were measured at 10-minute intervals over 24 hours in seven subjects, once with a normal nocturnal sleep from 2300 to 0700 hours, and once with a shifted daytime sleep from 0700 to 1500 hours. The subjects received continuous enteral nutrition and remained supine for the 8 hours preceding blood sampling and throughout the whole experiment. Insulin secretion rate was estimated by deconvoluting peripheral C-peptide levels using an open two-compartment model. The amplitude of glucose and insulin secretion rate oscillations increased by 160% during the 8-hour sleep periods, at whatever time they occurred, whereas the influence of the time of day was not significant. Glucose and insulin secretion rate mean levels were also significantly increased during normal nocturnal sleep compared to the remaining 8-hour waking periods, but this effect did not persist when sleep was shifted to the daytime. The number of oscillations was similar in both experimental series and was not affected by sleep. No systematic concordance was found between glucose and insulin secretion rate oscillations and the rapid eye movement-nonrapid eye movement sleep cycles, despite them having similar periodicities. This study demonstrates that increased amplitude of glucose and insulin secretion rate oscillations is related to sleep rather than to the time of day, without any associated frequency variations. The slightly higher mean glucose levels observed during the nighttime period possibly reflect a weak time-dependent influence.