Interrelationships between alpha and beta-anomers of glucose affecting both insulin and glucagon secretion in the perfused rat pancreas. II

Abstract

Temporal and quantitative relationships between the alpha and beta anomers of glucose on insulin and glucagon secretion were studied in two surgical preparations of the in vitro perfused rat pancreas. Alpha-Glucose was a more effective stimulator of insulin release. Beta-Glucose, however, though less effective, was a positive modulator when admixed with alpha-glucose. Dose-response studies showed that alpha-glucose probably had a smaller apparent Km for insulin secretion, while the Vmax for the two anomers was the same-the effects of the two anomers being indistinguishable at high glucose concentrations (300 mg/dl). Alpha-Anomeric stereospecificity was demonstrable equally on both phases of insulin release and was maintained throughout 60-min perfusions. Spontaneous or arginine-stimulated glucagon release was also preferentially inhibited by alpha-glucose. Since others have shown that glucose uptake and phosphorylation in islets are not alpha-stereospecific, the data suggest that the initial signal for the first and second phases of insuulin release and glucose suppression of glucagon secretion is at the level of a glucoreceptor prior to, or indedendent of, major pathways of glucose metabolism.