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Contribution of nitric oxide to β2-adrenoceptor mediated vasodilatation in human forearm arterial vasculature

Lookup NU author(s): Dr Nikhil Majmudar, Professor Steve Robson, Professor Gary Ford

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Abstract

Aims. β2-adrenoceptor agonists are generally considered to produce endothelium independent vasodilatation through adenylate cyclase. We determined whether nitric oxide contributes to β2-adrenoceptor vasodilatation in human arterial vasculature. Methods. Forearm blood flow responses to brachial intra-arterial infusions of ritodrine (2.5-50 μg min-1), a selective β2-adrenoceptor agonist, were determined in 24 healthy, normotensive subjects (mean age 22 years, 5F) on two occasions with initial and concomitant administration of L-NMMA (800 μg min-1), an NO synthase inhibitor, or noradrenaline (5-30 ng min-1), a control constrictor not affecting basal NO activity. Responses to the endothelium dependent vasodilator serotonin (n = 6) and an endothelium independent vasodilator GTN (n = 9) were also determined. Results. Maximal dilatation to ritodrine during L-NMMA infusion (310 ± 32%; mean + s.e. mean) was reduced compared to that during noradrenaline infusion (417 ± 41%, P < 0.05), as were summary responses (1023 ± 101 vs 1415 ± 130; P < 0.05). Responses to GTN were unaffected by L-NMMA compared to noradrenaline; max 177 ± 26 vs 169 ± 20%, 95% CI for difference - 33,48; P = 0.68; summary response 361 ± 51 vs 396 ± 37, 95% CI -142,71; P = 0.46. Dilator responses to serotonin were reduced by L-NMMA; max 64 ± 20 vs 163 ± 26%, P < 0.01; summary response 129 ± 36 vs 293 ± 60; P < 0.05) and to a greater extent than ritodrine (58 ± 7 vs 25 ± 14%, P < 0.05). Conclusions. β2-adrenoccptor mediated vasodilatation in the human forearm has an NO mediated component. The underlying mechanism for this effect is unclear, but flow mediated vasodilatation is unlikely to be responsible.


Publication metadata

Author(s): Majmudar NG, Anumba D, Robson SC, Ford GA

Publication type: Article

Publication status: Published

Journal: British Journal of Clinical Pharmacology

Year: 1999

Volume: 47

Issue: 2

Pages: 173-177

Print publication date: 01/01/1999

ISSN (print): 0306-5251

ISSN (electronic): 1365-2125

Publisher: Wiley-Blackwell Publishing

URL: http://dx.doi.org/10.1046/j.1365-2125.1999.00880.x

DOI: 10.1046/j.1365-2125.1999.00880.x

PubMed id: 10190652


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