Reperfusion injury in the endotoxin-treated rat heart: reevaluation of the role of nitric oxide.

1. The role of nitric oxide (NO) in ischaemia-reperfusion injury to the heart continues to be debated. 2. The role of NO released during endotoxemia on myocardial reperfusion injury was examined in rats given saline or lipopolysaccharide (LPS, 10 mg. kg-1). 3. Aortic rings from LPS-treated rats showed a markedly decreased contractile response to both noradrenaline (NA) and U46619, and a diminished relaxation response to acetylcholine, thrombin and aggregating platelets. Treatment of rat aortic rings from LPS-treated rats with the NO synthesis inhibitor N omega-nitro-L-arginine (L-NOARG) reversed the diminished contractile response to NE and U46619. 4. Before ischaemia-reperfusion, baseline force of cardiac contraction (FCC) and coronary perfusion pressure (CPP) were lower and coronary flow was higher in hearts from LPS-treated rats (all P < 0.05 vs. saline-treated group). Treatment of hearts from LPS-treated rats with L-NOARG increased baseline FCC and CPP. 5. After ischaemia-reperfusion, hearts from saline-treated rats showed a 36 +/- 5% fall in FCC, a 38 +/- 6% rise in CPP and a 38 +/- 5% fall in coronary flow, whereas hearts from LPS-treated rats revealed only a 16 +/- 9% fall in FCC, a 10 +/- 3% rise in CPP and a 20 +/- 4% fall in coronary flow (all P < 0.05 vs. changes in saline-treated group). Fewer hearts from LPS-treated rats developed reperfusion arrhythmias (6% vs. 60% hearts from saline-treated rats, P < 0.02). Myocardial superoxide dismutase activity was higher in the LPS-treated group (P < 0.05). 6. NO synthesis, measured as formation of nitrite, was higher (P < 0.05) in cardiac and aortic tissues from LPS-treated rats. Prostacyclin (PGI2) release in coronary effluent was greater in LPS-treated rat hearts (P < 0.05 vs. saline-treated rats). 7. Thus LPS-treated hearts demonstrate a basal decrease in FCC and coronary vascular resistance. These hearts demonstrate a modest protection from reperfusion injury. Induction of NO synthesis, and possibly PGI2 release, may underlie cardioprotection from ischaemia-reperfusion.