Previous clinical and experimental studies have indicated that ropivacaine, a local anaesthetic agent, exerts vasoconstrictor effects. In this study, the contractile effects of ropivacaine were investigated in vitro on mesenteric arteriolar beds obtained from 22 adult male C57BL/6J mice. The mesenteric arteriolar bed was perfused at constant rate (2 ml/min.) with oxygenated physiological salt solution using a roller pump. First we studied the effects of ropivacaine (3.2x10(-4) to 2.2x10(-2) mol/l) on the perfusion pressure and observed a dose-dependent pressor response, reaching a maximal increase of 26.0+/-3.7 mmHg. In a second study, we observed that after the mechanical removal of the endothelium ropivacaine-induced contractile responses were significantly reduced to a maximal of 13.5+/-0.7 mmHg. In a third set of experiments, we observed that under the effect of the cyclooxygenase inhibitor indomethacin (0.01 micromol/l) the ropivacaine-induced pressor response was significantly reduced to a maximal increase of 17.5+/-0.4 mmHg. This is the first evidence that this long-acting local anesthetic causes vasoconstriction in the perfused mesenteric arteriolar bed and that, at least in part, this effect is mediated by the endothelium since the cyclooxygenase inhibitor indomethacin reduced the ropivacaine-induced vasoconstriction to approximately 50%.