Superoxide anion mediates the endothelium-dependent contractions to serotonin by regenerated endothelium

The endothelium modulates vascular tone by releasing a variety of vasoactive compounds that relax or contract the underlying vascular smooth muscle. We have previously demonstrated that regenerated endothelium exhibits endothelium-dependent hypercontraction to the platelet-derived compound serotonin (or 5-HT). To determine if this hypercontraction is mediated by superoxide anion produced by the endothelium, we performed balloon catheter denudation on the thoracic and abdominal aorta of male Lewis rats. Eight weeks after arterial injury, endothelium-dependent responses to serotonin were examined in tissue bath experiments. Vascular rings (5 mm in length), with and without endothelium, were contracted with norepinephrine and then exposed to serotonin (10(-9) to 3 x 10(-5) mol/L). Vascular rings with regenerated endothelium exhibited hypercontraction to serotonin (251% +/- 25% of initial norepinephrine contraction; p less than 0.05 compared with control rings, 175% +/- 13%). Removal of the endothelium (133% +/- 6%) or treatment with superoxide dismutase (184% +/- 7%), with or without catalase, prevented the endothelium-dependent constrictor effect of the serotonin. Ketanserin suppressed the vasoconstrictor effect of serotonin on control (93% +/- 15%) and regenerated (105% +/- 9%) rings with endothelium, indicating that the serotonin effect is mediated through the 5-HT2-serotonergic receptor. Deferoxamine or heat-inactivated superoxide dismutase did not modify the response. These observations support the hypothesis that superoxide anion is an endothelium-derived contracting factor produced by regenerated endothelium after intimal injury.