Attenuation of Isoproterenol-Mediated Vasodilatation in Blacks

Abstract

The mechanism of enhanced vascular reactivity in young blacks, which may play a part in the development of hypertension, has not been defined. To determine the contribution of blunted vasodilatation mediated by β₂-adrenergic receptors to this phenomenon, we compared forearm blood-flow responses to isoproterenol in young black and white normotensive men. We used venous-occlusion plethysmography to measure the responses of blood flow in the forearm to the intraarterial administration of isoproterenol (10 to 400 ng per minute) in 9 normotensive black men (mean [±SD] age, 31.3±8.0 years) and 13 normotensive white men (mean age, 32.9±5.6 years). Sympathetic activity in the forearm was measured simultaneously by isotope-dilution techniques. Base-line blood flow in the forearm was similar in blacks and whites, but the degree of vasodilatation in response to isoproterenol was markedly lower in blacks. Isoproterenol at an infusion rate of 400 ng per minute produced a 9-fold increase in blood flow in whites but only a 3.5-fold increase in blacks (P2-adrenergic receptors. Our findings suggest that the mechanisms responsible for blunted vasodilatation in response to the administration of isoproterenol may contribute to enhanced vascular reactivity in blacks and may play a part in the pathogenesis of hypertension in blacks.