Effect of 6-wk estrogen withdrawal or replacement on myocardial ischemic tolerance in rats

Menopausal status is a risk factor for coronary artery disease death, but t he mechanism underlying this association is uncertain. To test whether estr ogen ameliorates the effects of acute myocardial ischemia in ways likely to translate into a mortality difference, we compared the response to brief ( 6-min) and prolonged (45-min) coronary occlusion in vivo in five groups (ea ch n = 16) of rats: ovariectomized females; ovariectomized females after 6 wk 17 beta-estradiol replacement; male rats supplemented with estradiol for 6 wk; normal males; and normal females. Coronary occlusion produced a unif orm ischemic risk area averaging 53 +/- 3% of left ventricular volume. Afte r a brief occlusion, reperfusion ventricular tachycardia/fibrillation occur red with >85% frequency in all groups. During a prolonged occlusion, ischem ic ventricular tachycardia occurred in 100% and sustained tachycardia requi ring cardioversion in >75% of rats in all groups. Myocardial infarct size a veraged 52 +/- 4% of the ischemic risk area and was similarly unaffected by gender or estrogen status. We conclude that neither short-term estrogen wi thdrawal, replacement, nor supplementation significantly affects the potent ially lethal outcomes from acute coronary occlusion in this species.