Insulin resistance in essential hypertension: a psychophysiological approach to the "chicken and egg" question.

Aims: High levels of plasma insulin have frequently been found in patients with high blood pressure. The causal role of insulin resistance in essential hypertension, however, is still debated. Epidemiological and clinical studies have not provided complete responses to the original pathophysiological speculations, while the suggestion that enhanced sympathetic tone may induce both insulin resistance and hypertension is gaining ground.

Data Synthesis: Many studies indicate that the high sympathetic drive in hypertensive patients originates within the brain, while other studies show that insulin resistance is associated with reduced vasodilatory capacity and increased vasoconstrictive functional responses ascribed to endothelial impairment. The sympathetic overdrive and enhanced cardiovascular reactivity, detectable since the earliest stages of hypertension lead to endothelial damage and, hence, impair the vasodilatory response, peripheral blood flow and flow-dependent metabolism. Thus, the link between hyperinsulinemia and high blood pressure might lie in the vascular abnormalities secondary to elevated sympathetic tone and exaggerated hemodynamic stress response.

Conclusions: Examination of the literature and the results of recent pilot studies of the stress systemic and regional hemodynamic reactivity in the present paper suggests that behavioral characteristics and cardiovascular stress responses play a pivotal role in determining the hyperinsulinemic state in hypertensive patients. High sympathetic tone, with consequent vascular impairment and altered functional responses, may be the primary event causing hyperinsulinemia and start very early in patients with high blood pressure. In turn, hyperinsulinemia further contributes to vascular damage and aggravates the metabolic and hypertensive disease.