Increased insulin receptors in carbohydrate-sensitive subjects: a mechanism for hyperlipaemia in these subjects?

Twenty male subjects, 11 normal and 9 carbohydrate-sensitive, participated in a study in which the effect of feeding diets low in copper (1.03 mg/d) on the number and affinity of insulin receptors was determined. Since carbohydrate-sensitive subjects are hyperinsulinaemic, it was anticipated that they would demonstrate a down-regulation of insulin receptors. The subjects were fed a low copper diet for 11 weeks and then replenished with copper (3 mg/d) for 3 weeks. Regardless of diets fed, carbohydrate-sensitive subjects showed increased insulin binding. The increase was due to the number of receptors without any change in their affinity. This unusual and unexpected observation in carbohydrate-sensitive subjects suggests an altered response of the insulin receptor, namely the failure of plasma insulin to down-regulate the number of receptors. It is possible that such an alteration could lead to a shift of the biological response curve of insulin to the left in some target tissues thereby causing hyperlipaemia by diverting glucose into triglyceride. The exact mechanism of hyperlipaemia in carbohydrate-sensitive subjects remains to be clarified.