Roles of NO and Ca2+-activated K+ channels in coronary vasodilation induced by 17beta-estradiol in ischemic heart failure.

Estrogen induces the generation of nitric oxide (NO) and produces coronary vasodilation by opening the Ca2+-activated K+ (K[Ca]) channels. The hypothesis that 17beta-estradiol produces NO and activates K(Ca) channels during coronary hypoperfusion was investigated. In open-chest dogs, the left anterior descending coronary artery was perfused through an extracorporeal bypass tube from the left carotid artery. 17beta-Estradiol was infused into the bypass tube for 20 min after coronary blood flow was reduced by partial occlusion of the bypass tube. 17beta-Estradiol increased the difference in NO concentrations between the coronary venous and arterial blood as well as coronary blood flow. The lactate extraction ratio and pH of coronary venous blood were both also increased by 17beta-estradiol, indicating a reduction in myocardial anaerobic metabolism. Whereas the increase in the coronary arteriovenous difference in NO concentration was completely attenuated by N(G)-nitro-L-arginine methyl ester (L-NAME, an inhibitor of NO synthase), the increase in coronary blood flow induced by 17beta-estradiol was only partially attenuated by L-NAME. The combination of L-NAME and iberiotoxin (a blocker of high-conductance K(Ca) channels) completely abolished the coronary vasodilatory effect of 17beta-estradiol. The data indicate that during coronary hypoperfusion in canine hearts, 17beta-estradiol increases coronary blood flow and improves metabolic dysfunction by increasing NO release and opening K(Ca) channels.