Impaired glucose tolerance in hypertension is associated with impaired insulin release independently of changes in insulin sensitivity

To assess the contribution of insulin release and glucose disposal by insulin-dependent and insulin-independent mechanisms to overall glucose tolerance in hypertension.

Minimal model analysis of insulin and glucose data from frequently sampled intravenous glucose-tolerance tests from 21 non-diabetic, newly diagnosed hypertensives, and from 21 age- and weight-matched normotensive controls, was performed to obtain indices of glucose tolerance, beta-cell function and insulin sensitivity.

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 first- 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 similar basal insulin and glucose concentrations, glucose tolerance was clearly 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 systolic (r = -0.44, P < 0.003) and diastolic (r = -0.42, P < 0.006) blood pressures. These differences were independent of body weight. Hypertensives also exhibited a lower fractional clearance rate for insulin.

Impaired insulin release might contribute to the glucose intolerance associated with hypertension, and this can occur in the absence of insulin resistance, which is not present in all subjects with essential hypertension.