BackgroundReperfusion after prolonged coronary artery occlusion may be followed by additional myocardial necrosis persisting for hours to days. Potential mechanisms include neutrophil-mediated injury and compromised flow within the microcirculation of the reperfused myocardium. Poloxamer 188 is a nonionic surfactant with beneficial hemorheological and neutrophil-inhibitory properties. The purpose of the present study was to determine if poloxamer 188 is capable of reducing the myocardial injury associated with sustained reperfusion and to examine the effect of treatment duration.Methods and ResultsThree groups of closed-chest dogs underwent 90 minutes of left anterior descending coronary artery occlusion (angioplasty balloon) and 72 hours of reperfusion. Poloxamer 188, formulated as RheothRx Injection (Burroughs Wellcome Co), was given as a 75 mg/kg IV bolus 15 minutes before reperfusion followed by a 150 mg·kg−1·h−1continuous IV infusion for 4 hours (n = 13) or 48 hours (n = 13); control dogs (n = 12) received saline for 48 hours. The 48-hour infusion of poloxamer 188 resulted in a 42% reduction in infarct size (as a percent of the area at risk) compared with the control group (25.0 ± 4.2% versus 43.3 ± 4.3%,P≤ .01), whereas the 4-hour group demonstrated a 25% reduction in infarct size compared with the control group (32.4 ± 4.3%,P= .08). ANCOVA demonstrated that the 48-hour infusion of poloxamer 188 reduced myocardial infarct size independent of differences in collateral blood flow (P= .002 versus control). A trend toward infarct size reduction was observed in the 4-hour infusion group (P= .098 versus control by ANCOVA). Plasma creatine phosphokinase concentration was lower in both poloxamer 188-treated groups (P< .05 versus control). Global left ventricular ejection fraction at 72 hours of reperfusion was improved in the 48-hour infusion group compared with the control group (43 ± 3.1% versus 33 ± 2.0%,P< .05), whereas ejection fraction in the 4-hour group was 37 ± 1.3% (P= NS versus control). Regional ventricular function was also significantly better in the 48-hour infusion group compared with the control group. In vitro studies demonstrated that at concentrations comparable to those achieved in vivo, poloxamer 188 inhibited neutrophil chemotaxis. This finding may represent a beneficial mechanism of action.ConclusionsA 48-hour infusion of poloxamer 188 reduced myocardial infarct size and improved left ventricular function in this dog model of 90 minutes of coronary artery occlusion and 72 hours of reperfusion. The finding that the 4-hour infusion of poloxamer 188 did not result in similar benefits suggests that additional reperfusion injury occurred between 4 and 48 hours.