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Selective AT 1 Receptor Antagonism Enhances Sympathetically Mediated Vasoconstriction in Man
Author(s) -
Lyons D,
Jackson SHD,
Swift CG
Publication year - 2007
Publication title -
clinical pharmacology and therapeutics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.941
H-Index - 188
eISSN - 1532-6535
pISSN - 0009-9236
DOI - 10.1038/sj.clpt.6100023
Subject(s) - losartan , vasoconstriction , medicine , angiotensin ii , placebo , angiotensin ii receptor type 1 , blood pressure , endocrinology , anesthesia , pathology , alternative medicine
The vasoconstrictive action of angiotensin II (AII) is partly, sympathetically mediated and angiotensin‐converting enzyme (ACE) inhibitors appear to exert a sympatholytic effect. We examine the effect of an orally administered, selective AT 1 receptor antagonist (losartan 50 mg) on sympathetically mediated vasoconstriction in healthy volunteers in an observer blind crossover study. Seven healthy, normotensive volunteers (21–32 years), were studied on two occasions at the end of each 6‐week treatment period (losartan or placebo). Forearm blood flow (FABF) (ml/dl forearm/min) was measured by venous occlusion plethysmography during the application of lower body negative pressure (LBNP) (−20 cm H 2 O) and at the end of each incremental infusion of norepinephrine (60, 120, and 240 pmol/min). Comparison of blood flow changes was by repeated measures analysis of variance; P <0.05 was taken as statistically significant. Losartan did not alter blood pressure compared to placebo. It did significantly enhance LBNP‐induced vasoconstriction in both the left arm compared to placebo (−36.6±3.4 vs −23.5±3.3% P =0.017) and the right arm compared to placebo (−39.5±3.8 vs −21.0±3.6% P =0.005). The FABF response to all doses of infused norepinephrine (60, 120, and 240 pmol/min) was also enhanced by losartan compared to placebo (−35.0±2.7 vs −18.2±6.0% −43.6±4.3 vs −28.6±5.8%, and −53.9±3.2 vs −42.5±6.8% P =0.057, respectively. Losartan enhances locally mediated sympathetic vasoconstriction in the forearm circulation of man, probably through its effect on circulating AII concentrations and we postulate that the adrenergic sympathetic constrictor action of AII is not mediated by the AT 1 receptor or is surmountable at this receptor. Clinical Pharmacology & Therapeutics (2007) 81 , 83–87. doi: 10.1038/sj.clpt.6100023

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