Impaired insulin secretion after oral sucrose and fructose in rats

The effects of sucrose and fructose on responses in plasma glucose and insulin to glucose given orally and/or iv were examined in unanesthetized, unrestrained rats. The plasma insulin response to oral administration of sucrose or a mixture of glucose and fructose was much lower than that to oral glucose despite the fact that plasma glucose responses to these administrations were similar. Oral administration fructose had no effect on the insulin response to iv infusion of glucose. Intravenous infusion of fructose also did not affect the plasma glucose and insulin responses to oral administration of glucose. The inhibitory effect of oral fructose on the insulin response to oral glucose was reversed by oral administration of soybean oil, which is known to stimulate insulin secretion induced by iv glucose. We conclude that the inhibitory effect of fructose on insulin secretion is mediated by some signals generated in the gastrointestinal tract.