Dynamics of insulin action in hypertension: assessment from minimal model interpretation of intravenous glucose tolerance test data

Based on glucose kinetics minimal model (GKMM) interpretation of frequently sampled intravenous glucose tolerance test (FSIGTT), the aim was to broaden the characterization of insulin-mediated glucose disposal in hypertension by aid of a dynamic insulin sensitivity index, S-I(D), and the related efficiency, eta = S-I(D)/S-I; of the metabolic system to convert the maximal individual response capacity, measured by S-I, into an effective insulin control on glucose. The C-peptide minimal model (CPMM) was used to interpret the role of beta-cell function. Plasma glucose, insulin, and C-peptide concentrations were measured, during a 5-h FSIGTT, in eighteen normoglycemic individuals: ten hypertensive patients (H-group) and eight normotensive subjects (N-group) with no metabolic syndrome. Compared to our N-group, the H-group showed a significant (P < 0.05) reduction of both S-I (56%) and S-I(D) (50%), no significant change of eta, a significant increase of both the first-phase beta-cell responsiveness to glucose (105%) and total insulin secretion (55%), and no significant change in disposition indexes, defined as the product of insulin sensitivity (either S-I and S-I(D)) and beta-cell responsiveness. These findings suggest that, in spite of no change of efficiency, insulin resistance in normoglycemic hypertensive patients is primarily compensated by an increase in first-phase insulin secretion to preserve glucose tolerance to intravenous glucose load.