Effect of ropivacaine on endothelium-dependent phenylephrine-induced contraction in guinea pig aorta

Background: Previous studies have shown that ropivacaine hasbiphasic vascular effects, causing vasoconstriction at low concentrations and vasorelaxation at high concentrations. This study was designed to examine the role of the endothelium during accidental intravascular absorption of ropivacaine, and to elucidate the mechanisms responsible. Methods: Isolated guinea pig aortic rings were suspended for isometric tension recording. The effects of ropivacaine on endotheliumintact and endothelium-denuded aortic rings were assessed. Endothelium-intact aortic rings were pre-contracted with phenylephrine before being exposed to ropivacaine and acetylcholine, in order to generate and compare concentration-response curves. In the absence and presence of yohimbine, propranolol, atropine, indometacin, N-G-nitro-L-arginine methyl ester (L-NAME), 1H-[1,2,4] oxadiazolo[4,3-a] quinoxalin-1-one (ODQ) or methylene blue, the contractile response induced by ropivacaine was assessed on endothelium-intact aortic rings pre-contracted with phenylephrine. Results: Ropivacaine (3 x 10(-4) to 10(-2) mol/l) produced vasoconstriction in endothelium-denuded aortic rings, whereas no such response was observed in aortic rings with intact endothelium. In phenylephrine pre-contracted intact aortic rings, ropivacaine induced a greater degree of vasorelaxation than did acetylcholine. Yohimbine, propranolol and atropine all failed to affect the relaxation responses induced by ropivacaine. However, pre-treatment with indometacin (cyclo-oxygenase inhibitor), L-NAME (nitric oxide synthase inhibitor), methylene blue (soluble guanylyl cyclase inhibitor) or ODQ (soluble guanylyl cyclase inhibitor), significantly decreased the ropivacaine-induced relaxation of endothelium-intact aortic rings (3 x 10(-4) to 10(-2) mol/l). Conclusions: Ropivacaine elicits an endothelium-dependent vasorelaxation in phenylephrine pre-contracted aortic rings via the nitric oxide-cyclic guanosine 30,50-monophosphate pathway and the prostaglandin system.