Physiological Importance of Deficiency in Early Prandial Insulin Secretion in Non-Insulin-Dependent Diabetes

Abstract

Patients with non-insulin-dependent diabetes mellitus (NIDDM) have a deficiency in early prandial insulin secretion. To determine the contribution of this early deficiency to prandial hyperglycemia, exogenous intravenous insulin (1.8 U over 30 min) was delivered to eight NIDDM subjects in a profile designed to simulate the normal initial rise in insulin levels. The same dose of insulin was also administered 1) in the same profile but delayed by 30 min and 2) as a constant infusion over 180 min. Augmentation of the early insulin response caused a 33 ± 4% reduction in the glycemic response to a mixed meal (P < .005); the peak blood glucose increment above baseline was reduced by 1.4 mM (P < .005) to an increment identical to nondiabetic subjects (3.3 ± 0.3 vs. 3.2 ± 0.2 mM), and blood glucose levels were still 0.9 mM lower after 180 min (P < .05). In contrast, the delayed profile or constant infusion did not significantly alter the glycemic response to the meal. Early insulin augmentation resulted in elevated peripheral insulin levels initially (peak level 81 ± 11 mU/L), but subsequent insulin and C-peptide levels were lower than in the control study (at 180 min after the meal, 22 ± 5 vs. 33 ± 8 mU/L, P < .05, and 4.0 ± 0.5 vs. 5.3 ± 0.6 μg/L, P < .02, respectively). Early insulin delivery caused free-fatty acid (FFA) levels to fall at a faster rate after the meal and also attenuated the initial rise in glucagon levels typical of NIDDM. We conclude that the deficiency in early prandial insulin secretion contributes to prandial hyperglycemia and late hyperinsulinemia and may be partially responsible for the abnormal FFA and glucagon responses in NIDDM.