Glucose insensitivity and amino-acid hypersensitivity of insulin release in rats with non-insulin-dependent diabetes. A study with the perfused pancreas

Abstract

Non-insulin-dependent diabetes (NIDDM) was obtained in adult rats following a neonatal streptozotocin injection. Rats with NIDDM exhibited slightly lowered plasma insulin, slightly elevated basal plasma glucose values (less than 200 mg/dl), and low pancreatic insulin stores (50% of the controls). Insulin secretion was studied in this model using the isolated perfused pancreas technique. Insulin response to glucose stimulation over the range 5.5-22 mM was lacking, thus indicating complete loss of B-cell sensitivity to glucose. Even in presence of theophylline, the B-cells remained insensitive to glucose. In contrast, glyceraldehyde elicited an insulin release as important as that obtained in the control pancreata. This could possibly suggest that the B-cell dysfunction in rats with NIDDM involves a block in glucose metabolism in the early steps of glycolysis prior to the triose-phosphate. Mannose stimulated insulin secretion less in the diabetics than in the controls. The insulin secretion obtained in response to isoproterenol indicated that the ability of the adenylcyclase to generate cAMP in the B-cells of the diabetics was not decreased. The insulinotropic actions of acetylcholine and tolbutamide were normal and increased, respectively, as compared with the controls. In the absence of glucose, the B-cells of the diabetics were unexpectedly hypersensitive to arginine and leucine. The alpha-ketoisocaproate effect in the diabetics was not significantly different from that obtained in the controls. The possibility that enhancement of insulin response to leucine in the diabetics might be related to a more active conversion of leucine to ketoisocaproate along the first steps of intraislet leucine metabolism is proposed.