Relationship of insulin, race, and hypertension with hemodynamic reactivity to a behavioral challenge

Insulin is a modulator of blood pressure and may play a role in the pathogenesis of hypertension. This study examined the relationship between fasting insulin level and cardiovascular reactivity in hypertensive and normotensive black and white patients. Eighty-one patients were studied after 3 days of hospitalization on an isocaloric diet providing 200 mmol Na+ and 100 mmol K+ per day. Fasting insulin levels were determined on the morning of the second hospital day; a median split was used to determine high- and low-insulin groups. On the next day of hospitalization we examined blood pressure and hemodynamic responses to a speaking challenge. Hemodynamic responses were determined with impedance cardiography. Reactivity was studied as the percentage change from resting baseline. There were significant race by blood pressure level interactions for systolic and diastolic blood pressure reactivity (P ≤ .01). Black hypertensives showed more blood pressure reactivity than either the white hypertensives or the white normotensives; black normotensives had less blood pressure reactivity than the other groups. Insulin grouping interacted with blood pressure level and race on the reactivity of the underlying hemodynamic measures (total peripheral resistance, stroke volume, and heart rate; P ≤ .02). Fasting insulin level had no relationship to blood pressure reactivity. On the other hand, insulin level interacted with blood pressure level and race on the underlying hemodynamics controlling blood pressure, namely total peripheral resistance and stroke volume. In black normotensives and white hypertensives, high insulin levels were associated with increased total peripheral resistance and decreased stroke volume during stress. No differences were observed in total peripheral resistance or stroke volume in black hypertensives. White normotensives with high insulin reacted with increases in stroke volume and decreased peripheral resistance, while low-insulin white normotensives reacted similarly to high-insulin white hypertensives. Therefore, insulin effects hemodynamic reactivity differentially among blacks and whites, normotensives and hypertensives.