Increased Vascular Adrenergic Vasoconstriction and Decreased Vasodilation in Blacks: Additive Mechanisms Leading to Enhanced Vascular Reactivity

Blood pressure reactivity is enhanced in young black subjects through mechanisms that are poorly understood. We compared α-adrenergic–mediated vasoconstrictor and β-adrenergic vasodilator sensitivity and their relation to sympathetic activity in blacks and whites. Ten healthy black (age, 29.9±2.4 years) and 10 white (age, 28.3±1.9 years) men were studied. Forearm blood flow was measured with strain-gauge plethysmography after the intrabrachial artery administration of phenylephrine (1.25 to 20 μg/min) and isoproterenol (60 and 400 ng/min) after application of lower-body negative pressure and after a cold pressor test. Forearm and systemic norepinephrine spillover were measured with a radioisotope dilution technique. α-Adrenergic vasoconstriction was markedly increased (ANOVA P =0.008) and β-adrenergic vasodilation decreased (ANOVA P =0.02) in blacks. Phenylephrine (10 μg/min) decreased forearm blood flow by 58.0±2.5% in blacks but only by 26.6±6.0% in whites (P