© 1999 by European Society of Cardiology
Copyright © 1999, European Society of Cardiology
Pharmacological characterisation of endothelium-dependent relaxation in human radial artery: comparison with internal thoracic artery
Departments of Medicine and Therapeutics and Cardiothoracic Surgery, Western Infirmary, Glasgow G11 6NT, UK
* Corresponding author. Tel.: +44-141-211-2042; fax: +44-141-339-2800.
Objective: The aim of this study was to investigate the contribution of nitric oxide/prostanoid-independent pathways to endothelium-dependent vasorelaxation in human conduit arteries. Methods: Rings of internal thoracic artery (ITA) and radial artery (RA) taken from patients undergoing coronary artery bypass graft surgery were suspended in 10-ml organ baths and relaxation to carbachol and bradykinin studied in the presence and absence of nitric oxide synthase (NOS) inhibitors and potassium channel blockers. Results: No significant relaxation to carbachol or bradykinin was observed in ITA after NOS inhibition. In contrast, in RA less than 40% attenuation of relaxation to carbachol or bradykinin was achieved with any of the NOS inhibitors. In the presence of 20 mM K+ relaxation to carbachol and bradykinin was inhibited by 28±9% and 42±9% while in the presence of L-NAME 200 µM+20 mM K+ relaxation was inhibited by 66±6% and 70±4% respectively in this artery. Tetraethylammonium, glibenclamide, apamin and iberiotoxin had little effect on relaxation to carbachol but charybdotoxin alone and charybdotoxin plus apamin attenuated relaxation to carbachol by 23±4% and 49±9% in RA. In the presence of L-NAME 200 µM attenuation of these relaxations were increased to 60±4% and 78±4%. Conclusion: In ITA relaxations to carbachol and bradykinin were mediated via nitric oxide. In contrast in RA, a conduit vessel of similar diameter, both nitric oxide-dependent and independent pathways appeared to contribute to vascular relaxation. This nitric oxide-independent relaxation involved opening of Ca2+ activated potassium channel(s). The existence of alternative pathways mediating endothelium-independent relaxation could be important under pathological conditions and may contribute to the long term survival of radial artery grafts.
KEYWORDS Human radial arteries; Potassium channels; Relaxation
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