Abnormal glucose modulation of islet A- and B-cell responses to arginine in non-insulin-dependent diabetes mellitus.

To assess the normality of islet A- and B-cell responses to a nonglucose secretogogue as well as the modulating effect of glucose in NIDDM, we examined plasma C-peptide and glucagon responses to arginine in eight patients with NIDDM and in six age- and weight-matched nondiabetic volunteers under conditions of identical hypoglycemia (approximately 70 mg/dl), euglycemia (94 mg/dl), and hyperglycemia (approximately 190 mg/dl). Plasma C-peptide responses to glucose and to arginine in the diabetic subjects were both significantly reduced at all glucose concentrations studied (P less than 0.01-0.005). The modulating effect of glucose on both islet A- and B-cell responses (slope of relation between plasma C-peptide or glucagon response versus plasma glucose concentration) was reduced greater than 80% in the diabetic subjects (P less than 0.01). We conclude that islet A- and B-cell responses to nonglucose secretogogues are abnormal in patients with NIDDM and that this may result from a functional defect in the modulating effect of glucose on insulin and glucagon secretion, which in some patients may be compensated for by hyperglycemia.