Chronic erythropoietin treatment limits infarct-size in the myocardium in vitro

It has been well established that erythropoietin (EPO) can limit myocardial ischemia/reperfusion injury in a variety of acute settings. However, despite EPO being used chronically to treat anemia the infarct limiting effects of long term treatment ( chronic) have never been fully investigated. In this study we examined the effects of a 3 week treatment of EPO ( 5,000 IU/Kg) in male Sprague Dawley rats in limiting myocardial infarction after 35 min ischemia and 2 h reperfusion in an in vitro isolated heart perfusion model. Treating the animals 'once a week' failed to limit infarct size significantly compared to a saline control (54.1% +/- 3.5 v 52.3% +/- 4.4), whereas a '3 times a week' regime succeeded in significantly reducing infarct size (36.2% +/- 3.2 v 52.3% +/- 4.4, p < 0.05). To demonstrate that the effect was not due to improved oxygen supply caused by a raised hematocrit level, we also administered EPO 24 h prior to ischemia/reperfusion. This treatment again reduced infarct size compared to a saline control (39.9% +/- 4.4 v 58.4% +/- 5.0, p < 0.05). To examine the mechanism of protection we used the PI3K inhibitor wortmannin and the nitric oxide synthase inhibitor L-NAME to try to abrogate EPO mediated protection. Where wortmannin failed to block the effects of EPO (31.7% +/- 6.0 v 36.2% +/- 3.2), L-NAME did abrogate protection (51.6% +/- 5.6 v 36.2% +/- 3.2, p < 0.05). We demonstrate that chronic EPO treatment limits infarct size and that it does so in a nitric oxide dependent manner.