CARBON-DIOXIDE INDUCED VASORELAXATION IN RAT MESENTERIC SMALL ARTERIES PRECONTRACTED WITH NORADRENALINE IS ENDOTHELIUM-DEPENDENT AND MEDIATED BY NITRIC-OXIDE

Hypercapnia induces initial constriction and prolonged relaxation of rat small mesenteric arteries. The mechanism of the relaxation is unknown, but has been attributed to lowering of pH(i) in the vascular smooth muscle. In this study we have investigated the response to raised PCO2 at constant pH(o), in mesenteric small arteries pre-contracted with noradrenaline. 10 % CO2 led to a fall in pH(i) associated with acute potentiation of tension, and subsequent relaxation. The relaxation did not occur in arteries in which the endothelium had been removed, nor in arteries pre-treated with the nitric oxide synthase inhibitor, L-NAME (10(-4) M, N-nitro-L-arginine methyl ester). The D-enantiomer, D-NAME, was without effect. We conclude that hypercapnic-induced vasodilatation in this circulation occurs via endothelium derived nitric oxide production.