(Hypertension. 2000;36:945.)
© 2000 American Heart Association, Inc.
Scientific Contributions |
Increased Vascular Adrenergic Vasoconstriction and Decreased Vasodilation in Blacks
Additive Mechanisms Leading to Enhanced Vascular Reactivity
From the Division of Clinical Pharmacology, Vanderbilt University School of Medicine, Nashville, Tenn.
Correspondence to Dr C. Michael Stein, Division of Clinical Pharmacology, Medical Research Bldg I, Room 560, Vanderbilt University School of Medicine, Nashville, TN 37232-6602.
Abstract—Blood pressure
reactivity is enhanced in young black subjects through mechanisms that
are poorly understood. We compared 
-adrenergic–mediated
vasoconstrictor and ß-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. -Adrenergic vasoconstriction was
markedly increased (ANOVA P=0.008) and ß-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<0.001). Vasoconstrictor response to
endogenous norepinephrine, stimulated by a cold
pressor test, resulted in a higher forearm vascular resistance in
blacks than in whites (107.3±13 versus 64.8±13 mm Hg ·
mL-1 · 100
mL-1, P=0.03). There were no
significant ethnic differences in basal or stimulated forearm or
systemic norepinephrine spillover. Increased
vasoconstrictor and decreased vasodilator responses in blacks were not
correlated. Increased sympathetically mediated vascular tone caused by
enhanced vasoconstriction and attenuated vasodilation, effects that
would be additive, and not increased sympathetic activity could enhance
vascular reactivity and may play a role in the pathogenesis of
hypertension in blacks.
Key Words: blacks • adrenergic agonists • vasoconstriction • vasodilation
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