OBJECTIVES: Adenosine monophosphate-activated protein kinase (AMPK) is a master regulator of energy metabolism and has been shown to be protective in ischaemia/reperfusion injury (IRI). We hypothesized that preactivation of AMPK with an activator before donor heart procurement could protect heart grafts from cold IRI. METHODS: Donor Sprague-Dawley rats were injected intravenously with AMPK activator 5-amino-imidazole-4-carboxamide ribonucleotide (AICAR) or vehicle 30 min before heart procurement. Heart grafts were then preserved in histidine-tryptophan-ketoglutarate (HTK) solution at 4 degrees C for 8 h. After preservation, grafts were immediately mounted on the Langendorff perfusion system and perfused with Krebs-Henseleit buffer at 37 degrees C for 1 h. Adenosine triphosphate (ATP) and malondialdehyde (MDA) content in graft tissue were quantified post-preservation and post-reperfusion. After reperfusion, isolated heart function was assessed using a pressure transducer; cumulative release of creatine kinase (CK) and lactate dehydrogenase (LDH) into the perfusate was measured to assess cardiomyocyte necrosis; ultrastructural changes in the mitochondria of the grafts were examined using transmission electron microscopy (TEM). RESULTS: After preservation, myocardial ATP content in the pretreated hearts was significantly higher than in the control hearts (3.247 +/- 0.3034 vs 1.817 +/- 0.2533 mu mol/g protein; P < 0.05). AICAR-pretreated heart grafts exhibited significantly higher coronary flow (9.667 +/- 0.3159 vs 8.033 +/- 0.2459 ml/min; P < 0.05) and left ventricular developing pressure (58.67 +/- 2.894 vs 42.67 +/- 3.333 mmHg; P < 0.05) than the vehicle treated after reperfusion. Cumulative release of CK (300.0 +/- 25.30 vs 431.7 +/- 42.39 U/l; P < 0.05) and LDH (228.0 +/- 16.68 vs 366.8 +/- 57.41 U/l; P < 0.05) in the perfusate was significantly lower in the AICAR-pretreated group than that in the control group. Myocardial MDA content was also reduced in the pretreated group (0.5167 +/- 0.1046 vs 0.9333 +/- 0.1333 nmol/mg protein; P < 0.05). TEM suggested that the mitochondrial structure of AICAR-pretreated hearts was much better preserved. Moreover, AICAR-pretreated hearts significantly diminished cytosolic cytochrome c release after reperfusion. CONCLUSIONS: This study demonstrates that pretreatment with AMPK activator AICAR significantly protects heart grafts from extended cold IRI. This novel protocol may be useful and feasible in clinical heart transplantation.