Copyright © European Society of Anaesthesiology. Unauthorized reproduction of this article is prohibited. Exogenous carbon monoxide does not affect cell membrane energy availability assessed by sarcolemmal calcium fluxes during myocardial ischaemia–reperfusion in the pig Katarina Ahlstro¨m, Bjo¨ rn Biber, Anna-Maja A ˚ berg, Pernilla Abrahamsson, Go¨ ran Johansson, Gunnar Ronquist, Anders Waldenstro¨ m and Michael F. Haney Carbon monoxide is thought to be cytoprotective and may hold therapeutic promise for mitigating ischaemic injury. The purpose of this study was to test low-dose carbon monoxide for protective effects in a porcine model of acute myocardial ischaemia and reperfusion. In acute open-thorax experiments in anaesthetised pigs, pretreatment with low-dose carbon monoxide (5% increase in carboxyhaemoglobin) was conducted for 120 min before localised ischaemia (45 min) and reperfusion (60 min) was performed using a coronary snare. Metabolic and injury markers were collected by microdialysis sampling in the ventricular wall. Recovery of radio-marked calcium delivered locally by microperfusate was measured to assess carbon monoxide treatment effects during ischaemia/reperfusion on the intracellular calcium pool. Coronary occlusion and ischaemia/reperfusion were analysed for 16 animals (eight in each group). Changes in glucose, lactate and pyruvate from the ischaemic area were observed during ischaemia and reperfusion interventions, though there was no difference between carbon monoxide-treated and control groups during ischaemia or reperfusion. Similar results were observed for glycerol and microdialysate 45 Ca 2þ recovery. These findings show that a relatively low and clinically relevant dose of carbon monoxide did not seem to provide acute protection as indicated by metabolic, energy-related and injury markers in a porcine myocardial ischaemia/reperfusion experimental model. We conclude that protective effects of carbon monoxide related to ischaemia/reperfusion either require higher doses of carbon monoxide or occur later after reperfusion than the immediate time frame studied here. More study is needed to characterise the mechanism and time frame of carbon monoxide-related cytoprotection. Eur J Anaesthesiol 2011;28:356–362 Published online 1 September 2010 Keywords: calcium, carbon monoxide, myocardial ischaemia, preconditioning, reperfusion, swine Introduction Carbon monoxide is produced in the body as a result of breakdown of haeme by haeme oxygenase and it is recog- nised to have a wide range of biological and physiological effects. 1 Carbon monoxide has been demonstrated to have effects on vascular tone, proliferation and apoptosis, leuco- cyte function and inflammation, platelet function and thrombosis, as well as other body systems. 2 Although carbon monoxide ingestion in higher levels through environmental exposure is recognised to be toxic, carbon monoxide-mediated cytoprotection is thought to hold therapeutic promise in applications to prevent ischaemic injury, 3,4 even possibly in doses in which the carbon monoxide is perceived as being at toxic levels. 5 Carbon monoxide has been recognised in recent years as conferring protective effects in pathophysiological situ- ations and this may be largely as a second messenger in one or several possible protective mechanisms, though the means of protection has not yet been proved. 6–11 Protective effects related to carbon monoxide adminis- tration before and during acute injury in vital organs and even in heart tissue during ischaemia/reperfusion injury have been shown, 12–17 though again the mechanism, specific timing and other related factors have not yet been clarified. Demonstration of protective effects of carbon monoxide in vital organs in experimental settings seems to be highly dependent on the specific models and conditions, the delivery or application of carbon mon- oxide, the timing and duration, the concentration and more. This study is designed to assess carbon monoxide as a possible therapeutic substance in the setting of acute myocardial ischaemia in a large animal model. In an earlier study, we reported energy metabolic effects of low-dose carbon monoxide administration in a model of acute myocardial ischaemia that suggested a more favourable condition related to carbon monoxide, though that study did not include demonstration of myocardial protection. 18 Therefore, we have aimed to test low-dose carbon monoxide for protective effects in a model of acute myocardial ischaemia and reperfusion using more robust assessment of metabolic conditions and injury. We hypothesised that carbon monoxide in a specific dose given as pretreatment would reduce injury and positively ORIGINAL ARTICLE From the Anesthesia and Intensive Care Medicine, Sahlgrenska Academy, University of Gothenburg, Gothenburg (KA, BB), Anesthesia and Intensive Care Medicine, Umea˚ University (A-MA ˚ , PA, MFH), Anesthesia and Intensive Care Medicine, University Hospital of Umea˚ (GJ), Umea˚, Department of Medical Chemistry, Uppsala University, Uppsala (GR) and Department of Cardiology, Umea˚ University, Umea˚ (AW), Sweden Correspondence to Michael Haney, Anesthesia and Intensive Care Medicine, University Hospital of Umea˚, 901 85 Umea˚, Sweden Tel: +46 90 785 2810; fax: +46 90 131388; e-mail: michael.haney@anestesi.umu.se 0265-0215 ß 2011 Copyright European Society of Anaesthesiology DOI:10.1097/EJA.0b013e32833eab96