There is enough evidence that erythropoietin (EPO) may be involved in cardiovascular function. Therefore we have investigated the possible effects of EPO on left ventricular developed pressure, +dP/dt max , heart rate, tissue cAMP, and nitrite levels. Isolated rat hearts were perfused under constant flow (10 ml/min) conditions with modified Krebs-Henseleit solution and recombinant human erythropoietin at doses of 100, 200, 500, and 1,000 IU/kg was administered as bolus injections. EPO at 100 IU/kg decreased, but higher doses (500 and 1,000 IU/kg) raised the developed pressure and +dP/dt max . However, it did not affect heart rate or coronary perfusion pressure when all the respective doses were applied. EPO at 100 IU/kg increased nitrite, and at 1,000 IU/kg it raised cAMP. Our results suggest that EPO may produce dose-dependently negative and positive inotropic effects on myocardial contractility in isolated rat hearts. NO and cAMP may be involved in negative and positive inotropic effects of EPO, respectively.Key words: erythropoietin, heart, contractility, cAMP, nitrite. It has been shown that recombinant erythropoietin (rHuEpo) is effective for the treatment of anemia associated with end-stage renal disease [13]. The treatment of renal anemia with EPO enhances cardiac output [14] and improves cardiac exercise performance [2]. EPO (10-200 IU/ml) induces a direct vasoconstrictor effect on renal resistance vessels [15], and intravenous EPO administration in hemodialysis patients causes an increase in plasma endothelin and blood pressure [16]. These findings suggest that EPO may play a role in the regulation of cardiovascular function.EPO-induced increase in intracellular cAMP has been indicated in mouse erythroleukemia SKT6 cells [17] and erythroblasts [18]. Cardiac myocytes and vascular endothelial cells produce nitric oxide (NO) via both constitutive and inducible isoforms of NO synthase [19]. NO stimulates cGMP formation, and EPO administration also increases plasma cGMP in rats [20]. It is possible that the effect of EPO on cardiac cell contractility might be mediated either alone by cAMP or by NO, or by both together.Since the effect of EPO on myocardial contractility, heart rate, and coronary perfusion pressure and the roles of cAMP and NO in contractile responses to EPO have not been investigated, we have decided to study these parameters on isolated perfused rat hearts.
MATERIALS AND METHODSLangendorff perfusion. Sprague-Dawley rats of either sex weighing 300-400 g were used. All procedures were applied in accordance with the Guiding Principles in the Care and Use of Animals. One hour after the administration of 1,000 IU heparin i.p., the chest was opened under light ether anesthesia, and the heart was excised rapidly and then placed into an ice-cold modified Krebs-Henseleit solution (mKHs) until contractions ceased. After the heart was cleansed of surrounding tissues, the aorta was immediately tied to a stainless steel perfusion cannula, and the heart was perfused retrogradely by the nonrecirc...
