, Volume 35, Issue 7, pp 681-689

Abnormalities in the ultradian oscillations of insulin secretion and glucose levels in Type 2 (non-insulin-dependent) diabetic patients

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To investigate the temporal organization of insulin secretion and glucose concentration during fasting in Type 2 (non-insulin-dependent) diabetes mellitus, we studied seven patients with Type 2 diabetes, eight obese non-diabetic control subjects and eight normal weight non-diabetic subjects. Blood sampling for glucose, insulin and C-peptide was performed at 15-min intervals during a 24-h period of fasting for the diabetic and the obese control subjects and during an 8-h fasting period for the normal subjects. Insulin secretion rates were calculated from the peripheral C-peptide concentration profiles. Ultradian oscillations of glucose levels and insulin secretion rates were evident during fasting in all subjects. An additional study with blood sampling at 2-min intervals for 8 h further indicated that this ultradian periodicity is expressed independently of rapid 10–15 min insulin oscillations. There were no differences between diabetic and nondiabetic subjects in the frequency of the ultradian oscillations of insulin secretion (which averaged 12–15 oscillations per 24 h) and in the rate of concomitancy of oscillations of insulin secretion with oscillations in glucose levels, which averaged 63–65%. The relative amplitudes of both the insulin and glucose oscillations were also similar in diabetic and nondiabetic subjects. The major abnormality in patients with Type 2 diabetes was evidenced by spectral analysis, and confirmed by calculations of the distributions of inter-pulse intervals. It consisted of a slowing of the glucose oscillations, without a similar slowing of the oscillations in insulin secretion. This slowing of the glucose oscillations in fasting Type 2 diabetic patients is consistent with our previous observations of sluggish and irregular glucose oscillations in diabetic subjects receiving mixed meals. This partial dissociation between the oscillatory patterns of insulin secretion and glucose levels could represent a sensitive quantitative marker of the breakdown of the insulin-glucose feedback loop in diabetes.