Effects of carbohydrates on insulin release from the isolated islets

Effects of monosaccharides and disaccharides on insulin release from the isolated islets were studied. Insulin release from the isolated islets was 26.2 microU/5 islets/hr in carbohydrate-free medium and increased by the addition of D-glucose or D-mannose. L-Glucose was ineffective by itself but potentiated the insulin release stimulated by D-glucose. Effects of glucuronic acid and N-acetyl-D-glucosamine on insulin release were similar to those of L-glucose. Among monosaccharides, 2-deoxy-D-ribose, D-galactosamine, L-fucose, N-acetylneuraminic acid and D-ribose decreased insulin release and had no effect on insulin release by D-glucose. D-Galactose and D-fructose also decreased insulin release. However, they potentiated the insulin release when D-glucose was also present. Cellobiose and lactose, which have a beta(1-4) linkage to glucose molecule at the reducing end, inhibited insulin release stimulated by D-glucose. On the other hand, sucrose and maltose lacking the beta(1-4) linkage, did not inhibit the insulin release stimulated by D-glucose. These results suggest that insulin release from the isolated islets is stimulated by carbohydrates which can be metabolized in B-cells. Non-metabolizable analogues of D-glucose or disaccharides show different effects on glucose transport or glucose metabolism in the B-cells according to their chemical structures.