Platelet-activating factor contributes to postischemic vasospasm

Background. The purpose of the present study was to determine if platelet-activating factor is an important mediator that produces vasospasm during reperfusion after ischemia in skeletal muscle. Materials and Methods. A vascular isolated cremaster muscle in male Sprague-Dawley rats was coupled with local intraarterial drug infusion as a model to study microcirculation responses to ischemia/ reperfusion injury. Arteriole diameters and capillary perfusion were measured using intravital microscopy. Group 1: platelet-activating factor dose response. Group 2: Effects of a cyclooxygenase inhibitor; indomethacin, and a thromboxane synthetase inhibitor, imidazole, on the response to platelet-activating factor. Group 3: Effects of nitric oxide synthesis inhibitor; N omega-nitro-L-arginine methyl ester, on the response to platelet-activating factor. Group 4: Effects of a platelet-activating factor receptor antagonist, CV-3988, indomethacin, and imidazole after 4 h of warm ischemia and reperfusion. Results. Intraarterial infusion of platelet-activating factor produced a dose-related but mild vasoconstriction. Pretreatment with indomethacin or imidazole resulted in significant vasodilation actually emanating from platelet-activating factor infusion. Nitric oxide inhibition (with N omega-nitro-L-arginine methyl ester) enhanced the vasoconstriction produced by platelet-activating factor. Pretreatment with CV-3988, indomethacin, or imidazole significantly attenuated ischemia/reperfusion-induced vasospasm and capillary no-reflow in the cremaster muscles. Conclusions. Ischemia/reperfusion-induced vasoconstriction is at least in part mediated by platelet-activating factor and thromboxane A(2). (C) 2000 Academic Press.