Protective effect of phloroglucinol against myocardial ischaemia-reperfusion injury is related to inhibition of myeloperoxidase activity and inflammatory cell infiltration.

1. It has been shown that phloroglucinol has anti-inflammatory and anti-oxidant properties. Both inflammatory cell infiltration and myeloperoxidase (MPO) activation play an important role in myocardial reperfusion injury. The aim of the present study was to explore the effect of phloroglucinol on myocardial reperfusion injury and the mechanisms involved. 2. Anaesthetized rats were pretreated with phloroglucinol (15 or 30 mg/kg, i.g.) or vehicle (5 mmol/L carboxymethyl cellulose sodium) 30 min prior to experimentation. The left main coronary artery was subjected to 1 h occlusion followed by 3 h reperfusion. Infarct size, the release of creatine kinase (CK), inflammatory cell infiltration, MPO activity and protein content, catalase in the blood and myocardium, and myocardial apoptosis were measured. 3. Following myocardial ischaemia and reperfusion in vehicle-treated rats, infarct size was 43.5 ± 3.7% (relative to the area at risk). Accompanying detrimental changes included elevated CK, enhanced inflammatory cell infiltration, high numbers of myocardial apoptotic cells, elevated caspase 3 activity, increased MPO activity and content in the plasma and myocardium and reduced catalase activity. These effects were attenuated by pretreatment with both doses of phloroglucinol (15 and 30 mg/kg, i.g.). 4. The results of the present study suggest that phloroglucinol protects the myocardium against ischaemia-reperfusion injury in rats and that its beneficial effects are related to inhibition of MPO activity and inflammatory cell infiltration.