Effects of carbohydrates on secretion of insulin from isolated rat pancreas

Abstract

The effect of carbohydrates on the secretion of immunochemically measurable insulin was studied in an isolated perfused pancreatic preparation from the rat. Degradation of circulating insulin (as measured by chromatographic examination of added insulin-I 131) was less than 15% during the 4-hr experimental period. Without the addition of glucose, or at glucose concentrations of less than 50 mg/100 ml, insulin secretion was not detectable. At glucose concentrations of 50–150 mg/100 ml, insulin secretion occurred immediately and persisted throughout the experimental period. Insulin secretion was further increased by increasing glucose concentration to 150–500 mg/100 ml. The incidence of islet cell degranulation increased with increasing insulin secretion, suggesting that glucose stimulated secretion of stored insulin faster than synthesis of insulin de novo. Galactose, xylose, l-arabinose, pyruvate, and 2-deoxyglucose in concentrations of 600 mg/100 ml did not stimulate insulin secretion. Mannose stimulated the pancreas equally as well as glucose. Fructose was also active, but was less effective than glucose. Neither 2-deoxyglucose nor galactose blocked the insulin secretion by glucose. The data suggest that secretion of insulin is stimulated by a metabolite or a product resulting from the metabolism of glucose which can also be supplied by other metabolizable sugars.