Peripheral adrenergic receptor contributions to cardiovascular reactivity: influence of race and gender

Ten White males, ten Black males, ten White females, and seven Black females (aged 22-48 yr) were exposed to a competitive reaction time task (enhancing beta-receptor activity), the forehead cold pressor (enhancing alpha-receptor activity), and a speech task on four separate occasions: twice under a saline placebo condition, once under a beta-blockade condition using i.v. propranolol, and once under a combined beta- and alpha-blockade condition using both i.v. propranolol and i.v. phentolamine. Order of placebo session and blockade session was counterbalanced across each race/gender group. Beta-blockade abolished the greater heart rate, cardiac index, and stroke volume index responses, and the lesser vascular tone seen under placebo in White vs. Black males. No differences between White and Black women were seen with or without beta-blockade. Gender differences in beta-receptor contribution to stress responses were restricted to the White subjects. Beta-blockade abolished the greater stroke volume index responses and less vascular tone observed in White males vs. White females. Although alpha-receptor blockade significantly decreased vascular resistance in each race/gender group, it did not differentially affect any of the subgroups. These data suggest that race and gender differences in cardiovascular stress responses of normotensive individuals are at least partly a function of differential beta-receptor activity/sensitivity. No clear support for differences in alpha-receptor activity/sensitivity was obtained.