Insulin infusion during normoglycemia modulates insulin secretion according to whole-body insulin sensitivity

Glucose is the major stimulus for insulin release. Time course and amount of insulin secreted after glycemic stimulus are different between type 2 diabetes mellitus (T2DM) patients and healthy subjects. In rodents, it was demonstrated that insulin can modulate its own release. Previous studies in humans yielded contrasting results: Insulin was shown to have an enhancing effect, no effect, or a suppressive effect on its own secretion. Thus, we aimed to evaluate short-term effects of human insulin infusion on insulin secretion during normoglycemia in healthy humans and T2DM subjects of both sex.

Hyperinsulinemic-isoglycemic clamps with whole-body insulin-sensitivity (M) and C-peptide measurements for insulin secretion modeling were performed in 65 insulin-sensitive (IS) subjects (45 ± 1 year, BMI: 24.8 ± 0.5 kg/m(2)), 17 insulin-resistant (IR) subjects (46 ± 2 years, 28.1 ± 1.3 kg/m(2)), and 20 T2DM patients (56 ± 2 years, 28.0 ± 0.8 kg/m(2); HbA(1c) = 6.7 ± 0.1%).

IS subjects (M = 8.8 ± 0.3 mg · min(-1) · kg(-1)) had higher (P < 0.00001) whole-body insulin sensitivity than IR subjects (M = 4.0 ± 0.2) and T2DM patients (M = 4.3 ± 0.5). Insulin secretion profiles during clamp were different (P < 0.00001) among the groups, increasing in IS subjects (slope: 0.56 ± 0.11 pmol/min(2)) but declining in IR (-0.41 ± 0.14) and T2DM (-0.87 ± 0.12, P < 0.00002 IR and T2DM vs. IS) subjects. Insulin secretion changes during clamp directly correlated with M (r = 0.6, P < 0.00001).

Insulin release during normoglycemia can be modulated by exogenous insulin infusion and directly depends on whole-body insulin sensitivity. Thus, in highly sensitive subjects, insulin increases its own secretion. On the other hand, a suppressive effect of insulin on its own secretion occurs in IR and T2DM subjects.