We investigated whether oestrogens modulate the phenomenon of leukocyte accumulation during ischaemia and reperfusion of the myocardium. Anaesthetized rats were subjected to total occlusion (1 h) of the left main coronary artery followed by 1 h reperfusion. Sham myocardial ischaemia-reperfusion rats (Sham) were used as controls. Myocardial necrosis, myocardial myeloperoxidase activity, serum creatinine phosphokinase activity, serum and macrophages tumour necrosis factor (TNF-alpha) and the myocardial staining of intercellular adhesion molecule-1 (ICAM-1) were evaluated. Myocardial ischaemia plus reperfusion in untreated rats produced marked myocardial necrosis, increased serum creatinine phosphokinase activity (348 +/- 38 U/ml) and cardiac myeloperoxidase activity, a marker of polymorphonuclear leukocyte accumulation, both in the area at risk and in the necrotic area (MPO 9 +/- 1.1 mU/g tissue and 8.2 +/- 1 mU/g tissue, respectively), and induced a marked increase in the macrophage (156 +/- 14 U/ml at the end of reperfusion) and serum (344 +/- 12 U/ml, at the end of reperfusion) levels of TNF-alpha. Finally, myocardial ischaemia-reperfusion injury increased ICAM-1 staining in the myocardium. Administration of 17beta-oestradiol (5, 10 and 20 microg/kg, i.m. 5 min after induction of myocardial ischaemia-reperfusion injury), lowered myocardial necrosis and myeloperoxidase activity in the area at risk and in the necrotic area, reduced serum and macrophages TNF-alpha (20 +/- 3 U/ml and 9 +/- 3 U/ml, respectively) and decreased serum creatinine phosphokinase activity (67 +/- 3 U/ml). Oestrogen treatment also blunted the increased staining of ICAM-1 in the injured myocardium. Finally, 17beta-oestradiol added in vitro to peritoneal macrophages collected from untreated rats subjected to myocardial ischaemia-reperfusion injury, significantly reduced TNF-alpha production. Our results suggest that 17beta-oestradiol, by inhibiting TNF-alpha production, limits the deleterious ICAM-1-mediated binding of leukocytes to injured myocardium and protects against myocardial ischaemia-reperfusion injury.