Effect of alpha-D-mannose and equilibrated D-mannose of insulin release

The effects on insulin release of alpha-D-mannose and equilibrated D-mannose were studied in the isolated perfused rat pancreas. Although phosphomannose isomerase, in contrast to phosphoglucose isomerase, is stereospecific for beta-D-mannose-6-phosphate, the alpha anomer of D-mannose (2 mg/ml) was significantly more effective than equilibrated D-mannose in stimulating insulin release. The finding does not seem to accord with the view that the signal for hexose-induced insulin release arises from the glycolytic pathway, and suggests the existence of the stereospecific glucoreceptor(s) on the pancreatic B-cell membrane.