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

Abstract

Menopausal status is a risk factor for coronary artery disease death, but the mechanism underlying this association is uncertain. To test whether estrogen 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 (each n = 16) of rats: ovariectomized females; ovariectomized females after 6 wk 17beta-estradiol replacement; male rats supplemented with estradiol for 6 wk; normal males; and normal females. Coronary occlusion produced a uniform ischemic risk area averaging 53 +/- 3% of left ventricular volume. After a brief occlusion, reperfusion ventricular tachycardia/fibrillation occurred with >85% frequency in all groups. During a prolonged occlusion, ischemic ventricular tachycardia occurred in 100% and sustained tachycardia requiring cardioversion in >75% of rats in all groups. Myocardial infarct size averaged 52 +/- 4% of the ischemic risk area and was similarly unaffected by gender or estrogen status. We conclude that neither short-term estrogen withdrawal, replacement, nor supplementation significantly affects the potentially lethal outcomes from acute coronary occlusion in this species.

Estrogen Reduces Cardiac Injury and Expression of β1-Adrenoceptor upon Ischemic Insult in the Rat Heart

“…This is in agreement with a recent study by McNulty et al (2000), who showed that estrogen withdrawal by ovariectomy for a 6-to 8-week period did not increase the myocardial infarct size of the isolated rat heart compared with normal and estrogenreplaced rats. On the other hand, the present study has shown that myocardial infarct size of female rats was smaller in response to ␤-AR stimulation during ischemia than that in Ovx rats and estrogen replacement restored the ability of the Ovx rats to resist ischemic injury.…”

The Effect of the Phytoestrogen Genistein on Myocardial Protection, Preconditioning and Oxidative Stress

“…Ovariectomy, 6 weeks prior to acute coronary occlusion in female rats, is associated with myocardial infarct size similar to intact animals [32] and this is in accordance with our findings. In mice, however, gonadectomy in females, 6 weeks earlier, induced larger myocardial infarctions compared to controls [33]; in the same study, gonadectomy cancelled the protection of preconditioning whereas we found that ovariectomy does not affect the effect of preconditioning.…”

Effects of ovarian sex hormones and downhill running on fiber-type-specific HSP70 expression in rat soleus

“…In accordance with our laboratory's previous studies (39,43), serum estrogen concentration in the E animals was approximately eight-to ninefold higher compared with both S and P animals and was at the high end of normal for rodents (23,39,52). The E animals were significantly lighter than both S and P animals, which is believed to be due to differences in insulin-like growth factor-1 and growth hormone release, which are downregulated by estrogen (7,39).…”