Differential Role of K-Atp Channels Activated by Conjugated Estrogens in the Regulation of Myocardial and Coronary Protective Effects

Abstract

Background-We have demonstrated that estrogen can reduce myocardial injury in ischemia-reperfusion via activation of ATP-sensitive potassium ( K-ATP) channels. We sought to determine whether the protective effect of estrogen extends to epicardial coronary artery with attenuated vasoconstriction in patients after angioplasty by activation of such channels. Methods and Results-The study was designed to prospectively investigate 41 consecutive patients scheduled for elective coronary angioplasty. Pretreatment with estrogen limited myocardial ischemia during coronary occlusion and attenuated postangioplasty coronary vasoconstriction at the dilated and distal segments . An inhibitor of K- ATP channels, glibenclamide, did not affect coronary vasomotor response, although it abolished the beneficial effect of estrogen on myocardial ischemia. Patients to whom estrogen was administered after the second balloon deflation experienced a similar magnitude of myocardial ischemia as controls but showed significantly attenuated vasoconstriction compared with controls (P=0.0001 ). Endothelia-1 levels from the great cardiac vein rose significantly from 1.9+/-0.4 to 3.1+/-0.6 pg/mL (P=0.001) 15 minutes after angioplasty in the control group; this was attenuated after estrogen was administered. Significant correlation was found between the changes in coronary vasomotion of the dilated segment and endothelia-1 levels (r =0.65, P<0.0001). Conclusions-These results demonstrate that estrogen is protective against both myocardial ischemia and coronary vasoconstriction through different mechanisms. The myocardial effect of estrogen was abolished by glibenclamide, which suggests that the cardioprotective effect of estrogen may result from activation of K-ATP channels. In contrast, estrogen-induced attenuated vasoconstriction is associated with an attenuated release of endothelin-1, independent of K- ATP activation.