Decreased Responsiveness of Superficial Hand Veins to Phenylephrine in Black Normotensive Males

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Abstract
Essential hypertension is more prevalent among blacks than whites although the explanation is unknown. It is possible that an altered vascular adrenoceptor responsiveness in blacks may play a role in the etiology of this racial difference. To test this hypothesis, we have compared the diameter changes in superficial veins in response to phenylephrine, an .alpha.-adrenergic agonist, and to isoproterenol, a .beta.-adrenergic agonist, in black and white young normotensive males using the dorsal hand vein compliance technique. The maximal venoconstriction after phenylephrine (Emax) was 92 .+-. 9% (mean .+-. SD) in the whites but only 74 .+-. 12% in the blacks (p = 0.00046). The ED50 of phenylephrine was 342 ng/min (geometric mean) in whites and 245 ng/min in blacks (p = 0.50). The Emax and ED50 for isoproterenol-mediated venodilation was not significantly different between the racial groups. These results indicate a decreased maximal responsiveness to .alpha.-adrenergic stimulation in normotensive blacks. How these changes relate to cardiovascular alterations in hypertensive blacks requires further study.