The Stimulus‐Secretion Coupling of Glucose‐Induced Insulin Release

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Abstract
1. The possible significance of the insular sorbitol pathway in glucose‐induced insulin release was investigated.2. Glucose, but neither fructose nor galactose, stimulated sorbitol synthesis by isolated islets. Aldose reductase inhibitors such as 2,4‐dimethylglutaric and 3,3‐tetramethylene glutaric acid abolished the glucose‐induced sorbitol formation, but failed to affect glucose‐induced insulin release. About 75% of the sorbitol formed by the islets was recovered in the incubation medium, the efflux of sorbitol occurring independently of insulin release. Exogenous fructose and sorbitol exerted a modest insulinotropic action characterized by a shift to the left of the sigmoidal curve relating insulin release to glucose concentration. The relative insulinotropic potency of glucose (100%), fructose (16%) and sorbitol (7%) paralleled their rate of oxidation by the isolated islets.3. These data suggest that metabolism through the sorbitol pathway plays little role in the process of glucose‐induced insulin release, although exogenous sorbitol exerts a modest insulinotropic action.

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