Cm. Stein et al., Increased vascular adrenergic vasoconstriction and decreased vasodilation in blacks - Additive mechanisms leading to enhanced vascular reactivity, HYPERTENSIO, 36(6), 2000, pp. 945-951
Citations number
31
Categorie Soggetti
Cardiovascular & Respiratory Systems","Cardiovascular & Hematology Research
Blood pressure reactivity is enhanced in young black subjects through mecha
nisms that are poorly understood, We compared alpha -adrenergic-mediated va
soconstrictor and beta -adrenergic vasodilator sensitivity and their relati
on 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. Fore
arm blood flow was measured with strain-gauge plethysmography after the int
rabrachial artery administration of phenylephrine (1.25 to 20 mug/min) and
isoproterenol (60 and 400 ng/min) after application of lower-body negative
pressure and after a cold presser test. Forearm and systemic norepinephrine
spillover were measured with a radioisotope dilution technique, alpha -Adr
energic, vasoconstriction was markedly increased (ANOVA P=0.008) and beta -
adrenergic vasodilation decreased (ANOVA P=0.02) in blacks. Phenylephrine (
10 mug/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 presser test, resulted in a higher for
earm 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 diff
erences in basal or stimulated forearm or systemic norepinephrine spillover
. Increased vasoconstrictor and decreased vasodilator responses in blacks w
ere not correlated. Increased sympathetically mediated vascular tone caused
by enhanced vasoconstriction and attenuated vasodilation, effects that wou
ld be additive, and not increased sympathetic activity could enhance vascul
ar reactivity and may play a role in the pathogenesis of hypertension in bl
acks.