• Anna Mitchell, Uljana Rushentsova, Winfried Siffert, Thomas Philipp, and Rene R Wenzel.
• Department of Nephrology and Hypertension and Institute of Pharmacology, University of Duisburg-Essen Medical School, Essen, Germany. anna.mitchell@uni-essen.de
• Clin. Pharmacol. Ther. 2006 Mar 1;79(3):274-81.

ObjectiveWe investigated the influence of angiotensin II receptor blockade on angiotensin II-induced, endothelin 1 (ET-1)-induced, and norepinephrine-induced vasoconstriction to further characterize interactions of the 3 major pressor systems. ET-1, angiotensin II, and norepinephrine act via G protein-coupled receptors with a possible involvement of the G-protein beta3 subunit (GNB3) C825T polymorphism. We studied the influence of this polymorphism on the responses to angiotensin II antagonism in the presence of ET-1, norepinephrine, and angiotensin II.MethodsTwenty-five healthy men (mean age, 28.6 +/- 4 years; n = 14 CC, n = 9 CT, and n = 2 TT) were included in a double-blind, randomized, placebo-controlled crossover study. We used a laser Doppler imager to evaluate skin perfusion changes after injection of ET-1, angiotensin II, and norepinephrine (10(-18), 10(-16), and 10(-14) mol) after oral intake of the angiotensin II receptor antagonist valsartan (80 mg) or placebo. Data were analyzed with ANOVA or t test and are expressed as arbitrary perfusion units (PU) (mean +/- SEM).ResultsValsartan abolished angiotensin II-induced vasoconstriction and, more importantly, also ET-1-induced vasoconstriction in the skin microcirculation (ET-1 placebo versus valsartan, - 33 +/- 10 PU versus +33 +/- 21 PU for CC [P = .02] and -71 +/- 25 PU versus +108 +/- 21 PU for CT/TT [P < .001]). For both ET-1 and angiotensin II, valsartan effects were greater in GNB3 835T-allele carriers (P = .007 and P = .03 for ET-1 and angiotensin II, respectively, for CC versus CT/TT). Norepinephrine-mediated constriction was not influenced by valsartan. These effects were independent of blood pressure.ConclusionOur results indicate that the renin-angiotensin system may significantly contribute to ET-1-mediated microvascular responses. Valsartan inhibited local vasoconstriction to angiotensin II and ET-1 to a greater degree in carriers of the GNB3 825T allele, which adds to data from earlier studies implicating the C825T polymorphism as a pharmacogenetic marker for drug effects.

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