The Effects of Glucose, N-Acetylglucosamine, Glyceraldehyde and Other Sugars on Insulin Release in Vivo

The specificity for carbohydrates of insulin secretory responses in vivo was studied. Test sugars were injected via a left femoral vein cannula into conscious rats. Blood samples collected over the ensuing 60 min via a left femoral arterial cannula were assayed for plasma insulin and glucose, and, in some experiments, for N-acetyl glucosamine. Whereas L-glucose or saline produced no significant changes in plasma insulin or glucose concentrations, D-glucose, N-acetylglucosamine, D-glucosamine, fructose, D-glyceraldehyde and DL-glyceraldehyde were potent secretagogues. Simultaneous injection of mannoheptulose abolished the insulin-otropic action of glucose and N-acetylglucosamine, but not of DL-glyceraldehyde. Fructose, glucosamine, and DL-glyceraldehyde induced hyperglycaemia, but peak insulin concentrations occurred before any change in plasma glucose concentration. No evidence was obtained for a stimulatory effect of galactose on insulin release. Infusion for 60 min of N-acetylglucosamine produced a sustained elevated plasma insulin concentration and significant hypoglycaemia. The present in vivo results agree with previous in vitro observations, and could indicate a role for sugars other than glucose in the regulation of insulin release.