Myocardial function improved by electromagnetic field induction of stress protein hsp70

Studies on myocardial function have shown that hsp70, stimulated by an increase in temperature, leads to improved survival following ischemia-reperfusion (I-R). Low frequency electromagnetic fields (EMFs) also induce the stress protein hsp70, but without elevating temperature. We have examined the hemodynamic changes in concert with EMF pre-conditioning and the induction of hsp70 to determine whether improved myocardial function occurs following I-R injury in Sprague-Dawley rats. Animals were exposed to EMF (60 Hz, 8 mu T) for 30 min prior to I-R. Ischemia was then induced by ligation of left anterior descending coronary artery (LAD) for 30 min, followed by 30 min of reperfusion. Blood and heart tissue levels for hsp70 were determined by Western blot and RNA transcription by rtPCR. Significant upregulation of the HSP70 gene and increased hsp70 levels were measured in response to EMF pre-exposures. Invasive hemodynamics, as measured using a volume conductance catheter, demonstrated significant recovery of systolic contractile function after 30 min of reperfusion following EMF exposure. Additionally, isovolemic relaxation, a measure of ventricular diastolic function, was markedly improved in EMF-treated animals. In conclusion, non-invasive EMF induction of hsp70 preserved myocardial function and has the potential to improve tolerance to ischemic injury.