IMPAIRED GLUCOSE-TOLERANCE IN HYPERTENSION IS ASSOCIATED WITH IMPAIRED INSULIN RELEASE INDEPENDENTLY OF CHANGES IN INSULIN SENSITIVITY

Objective: To assess the contribution of insulin release and glucose d isposal by insulin-dependent and insulin-independent mechanisms to ove rall glucose tolerance in hypertension. Design and methods: Minimal mo del analysis of insulin and glucose data from frequently sampled intra venous glucose-tolerance tests from 21 non-diabetic, newly diagnosed h ypertensives, and from 21 age- and weight-matched normotensive control s, was performed to obtain indices of glucose tolerance, beta-cell fun ction and insulin sensitivity. Results: Intravenous glucose tolerance (defined as the glucose disappearance rate constant) was significantly correlated with the minimal model parameters for insulin sensitivity, glucose effectiveness or insulin-independent glucose uptake, and firs t- and second-phase beta-cell responsiveness (phi(1) and phi(2)) First -phase insulin release, expressed either as the area under the insulin -time curve between 0 and 10 min or as the ratio of that area to total insulin area was also correlated with glucose tolerance. Despite simi lar basal insulin and glucose concentrations, glucose tolerance was cl early diminished among the hypertensives. This could not be accounted for by insulin resistance or by changes in insulin-independent glucose uptake. Insulin release was diminished, as evidenced by the lower phi (2) among the hypertensives. phi(2) was inversely correlated with syst olic (r = -0.44, P < 0.003) and diastolic (r = -0.42, P < 0.006) blood pressures. These differences were independent of body weight. Hyperte nsives also exhibited a lower fractional clearance rate for insulin. C onclusion: Impaired insulin release might contribute to the glucose in tolerance associated with hypertension, and this can occur in the abse nce of insulin resistance, which is not present in all subjects with e ssential hypertension.