Intermedin (IMD) is a novel member of the calcitonin/calcitonin gene-related peptide (CT/CGRP) family identified from human and other vertebrate tissues. Preprointermedin (preproIMD) can generate a 47 amino acid mature peptide (IMD1-47) and a shorter 40 amino acid one (IMD8-47) by proteolytic cleavage. Amino acid sequence analysis showed that cleavage sites are located between two basic amino acids at Arg93-Arg94, resulting in the production of preproIMD(95-147), namely IMD1-53. The present study was designed to observe the effects of IMD1-53 on cardiac function in ischemia/reperfusion (I/R) injury in isolated rat hearts. Perfusion with high-dose IMD1-53 gave higher left ventricular systolic pressure (LVSP) and maximal rate of increase and decrease of left ventricle pressure ( +/-LVdP/dt(max)), and coronary perfusion flow (CPF) than those of controls. Cardiac I/R induced a marked inhibition of cardiac function and myocardial injury. Reperfusion with IMD1-53 significantly ameliorated the inhibited cardiac function and bradycardia induced by I/R. Compared with the I/R-treatment alone, IMD1-53 reperfusion augmented CPF, LVSP, and maximal rate of increase and decrease of left ventricle pressure (+/-LVdP/dt(max)) and decreased LVDP. In addition, reperfusion with IMD1-53 markedly attenuated the leakage of lactate dehydrogenase and malondialdehyde content in myocardia compared with I/R alone. Reperfusion with IMD(1-53)increased the content of cyclic adenosine monophosphate in comparison with I/R alone. Interestingly, the above IMD1-53 effects are similar to those of adrenomedullin. These results suggest that IMD1-53, like adrenomedullin, has cardioprotective effects against myocardial I/R injury. (C) 2004 Elsevier Inc. All rights reserved.