Endothelin-1 does not contribute to ischemia/reperfusion-induced vasoconstriction in skeletal muscle

The experiment reported was designed to investigate whether endothelin-1 (ET-1) contributes to vasospasm and poor perfusion during the reperfusion after prolonged ischemia in skeletal muscle. Male Sprague-Dawley rats weighting 100 to 120 g were anesthetized with Nembutal. The vascular isolated rat cremaster muscle, coupled with local interarterial infusion, was the model used in this study. The diameters of feeding arterioles and terminal arterioles were measured utilizing intravital microscopy. The number of terminal arterioles with temporary cessation of flow were counted in each cremaster. Group 1: ET-dose response (8 rats)--various concentrations of ET-1 (from 10(-8) M to 10(-5) M) were infused into the cremaster to test whether this muscle was responsive to the agent in a dose-dependent manner. Group 2: ET-antagonist response (12 rats)--PD-142893, 10(-4) M (ETab receptor antagonist) plus ET-1 10(-7) M were infused into the cremaster to test whether vasospasm caused by exogenous ET-1 could be prevented by pretreatment with this specific ETab receptor antagonist. Group 3: ischemia/reperfusion response (12 rats)--PD-142893, 10(-4) M was infused into the cremaster before ischemia (4 hr warm ischemia) and during reperfusion to test whether ETab receptor antagonism was effective in preventing the vasospasm associated with ischemia/reperfusion injury. The results from this study show that a mixed ETab endothelin antagonist, PD-142893, infused before ischemia and during reperfusion at a dose which virtually abolished the vasoconstriction produced by a high concentration of exogenous endothelin-1, had no effect on ischemia/reperfusion-induced vasoconstriction in this model. These results suggest that ET-1 probably does not contribute to the ischemia/reperfusion-induced vasoconstriction and poor reflow in rat skeletal muscle.