Chronically administered acetaminophen and the ischemia/reperfused myocardium

Male and female Hartley strain guinea pigs weighing 280 +/- 10 g were given acetaminophen-treated water ad libitum for 10 days. Sham-treated control animals were given similar quantities of untreated tap water (vehicle-treated control group). On Day 10, hearts were extracted, instrumented, and exposed to an ischemia (low-flow, 20 min)/reperfusion protocol. Our objective was to compare and contrast ventricular function, coronary circulation, and selected biochemical and histological indices in the two treatment groups. Left ventricular developed pressure in the early minutes of reperfusion was significantly greater in the presence of acetaminophen, e.g., at 1 min, 40 +/- 4 vs 21 +/- 3 mmHg (P < 0.05). Coronary perfusion pressure was significantly less from 3 to 40 min of reperfusion in the presence of acetaminophen. Creatine kinase release in vehicle-treated hearts rose from 42 +/- 14 (baseline) to 78 +/- 25 units/liter by the end of ischemia. Corresponding values in acetaminophen-treated hearts were 36 +/- 8 and 44 +/- 14 units/liter. Acetaminophen significantly (P < 0.05) attenuated release of creatine kinase. Chemiluminescence, an indicator of the in vitro production of peroxynitrite via the in vivo release of superoxide and nitric oxide, was also significantly attenuated by acetaminophen. Electron microscopy indicated a well-preserved myofibrillar ultrastructure in the postischemic myocardium of acetaminophen-treated hearts relative to vehicle-treated hearts (e.g., few signs of contraction bands, little or no evidence of swollen mitochondria, and well-defined light and dark bands in sarcomeres with acetaminophen; opposite with vehicle). We conclude that chronic administration of acetaminophen provides cardioprotection to the postischemic, reperfused rodent myocardium.