Race, borderline hypertension, and hemodynamic responses to behavioral stress before and after beta-adrenergic blockade

Blood pressure (BP) and hemodynamic responses (cardiac output [CO] and total peripheral resistance [TPR]) to a competitive reaction-time task, previously shown to increase beta-adrenergic activity, were compared in 20 Black and 20 White young men, once following infusion of saline placebo and later repeated after infusion of the nonselective beta-antagonist, propranolol. Both racial groups included subjects with marginal systolic BP (SBP) elevations (n = 6 Whites, n = 5 Blacks) and subjects with normal BP (n = 14 Whites, n = 15 Blacks). Blacks with marginal SBP elevations showed greater diastolic BP increases during the stressor than their White counterparts, both before and after beta-blockade. Both Blacks and Whites with marginal SBP elevations showed greater CO increases during the task than normotensives prior to blockade. Independent of BP status, Black subjects consistently showed higher TPR responses to the task than Whites (lesser decreases before blockade and greater increases after blockade). Blacks also showed greater diminution than Whites after blockade in ionotropic myocardial responses (stroke volume, pre-ejection period, and CO) to the stressor. The possible contributions of alpha-adrenergic and beta-adrenergic influences to these racial group differences are discussed.