Hearts isolated from non-insulin-dependent diabetic rats were found to exhibit reduced rates of basal and insulin-stimulated glucose metabolism. Since tissue levels of fructose 1,6-bisphosphate are significantly reduced in the diabetic heart, it was concluded that phosphofructokinase may be inhibited. However, neither glycogen nor glucose 6-phosphate accumulated in the myocyte, indicating that the phosphofructokinase reaction was not a bottleneck diverting substrate away from glycolysis. The other major factor contributing to decreased glycolytic flux in the diabetic heart is the impairment in glucose transport. Both basal and insulinstimulated transport of 3-O-methyl-D-glucose was 30% less in the diabetic heart/While insulin sensitivity was unaltered in the diabetic rat, insulin responsiveness was decreased, indicating that the impairment in insulin-stimulated hexose transport was caused by a postreceptor defect. The net result of these abnormalities in glucose metabolism is a significant reduction in the rate of ATP synthesis by the diabetic heart.

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