Opposite effects of nitric oxide and nitroxyl on postischemic myocardial injury

Abstract

Recent experimental evidence suggests that reactive nitrogen oxide species can contribute significantly to postischemic myocardial injury. The aim of the present study was to evaluate the role of two reactive nitrogen oxide species, nitroxyl (NO(-)) and nitric oxide (NO(.)), in myocardial ischemia and reperfusion injury. Rabbits were subjected to 45 min of regional myocardial ischemia followed by 180 min of reperfusion. Vehicle (0.9% NaCl), 1 micromol/kg S-nitrosoglutathione (GSNO) (an NO(.) donor), or 3 micromol/kg Angeli's salt (AS) (a source of NO(-)) were given i.v. 5 min before reperfusion. Treatment with GSNO markedly attenuated reperfusion injury, as evidenced by improved cardiac function, decreased plasma creatine kinase activity, reduced necrotic size, and decreased myocardial myeloperoxidase activity. In contrast, the administration of AS at a hemodynamically equieffective dose not only failed to attenuate but, rather, aggravated reperfusion injury, indicated by an increased left ventricular end diastolic pressure, myocardial creatine kinase release and necrotic size. Decomposed AS was without effect. Co-administration of AS with ferricyanide, a one-electron oxidant that converts NO(-) to NO(.), completely blocked the injurious effects of AS and exerted significant cardioprotective effects similar to those of GSNO. These results demonstrate that, although NO(.) is protective, NO(-) increases the tissue damage that occurs during ischemia/reperfusion and suggest that formation of nitroxyl may contribute to postischemic myocardial injury.

Figure 1

Formation of nitric oxide (NO^⋅) from Angeli’s salt (AS) (100 nmol) in the absence and presence of reduced glutathione (1 μmol) and potassium ferricyanide (PF) (100 nmol). Experiments were carried out either in the absence (filled columns) or presence of oxygen (hatched columns). Depicted data are means ± SEM from 3–5 independent experiments.

Figure 2

Pressure–rate index (PRI), left ventricular end diastolic pressure (LVEDP), and maximal first derivative of left ventricular pressure (dP/dt_max) in rabbits under control conditions and after animals have been subjected to MI/R treated with vehicle (saline), S-nitrosoglutathione (GSNO) (1 μmol/kg), Angeli’s salt (AS) (3 μmol/kg), potassium ferricyanide (PF) (10 μmol/kg), or a combination of AS and PF (3 and 10 μmol/kg, respectively). *, P < 0.05, vs. the vehicle-treated rabbits.

Figure 3

Plasma creatine kinase (CK) activity expressed as units per gram of protein measured before ischemia (0), at the end of ischemia (I-45), and hourly thereafter for the main five treatment groups. *, P <0.05; **, P < 0.01 vs. the vehicle-treated group.

Figure 4

Tissue wet weight of the area at risk (AAR) as a percentage of the total left ventricular (LV) wet weight and of necrotic tissue (NEC) as a percentage of area at risk and of the total left ventricle for the main five treatment groups. **, P < 0.01, vs. the vehicle-treated rabbits.

Figure 5

Tissue myeloperoxidase (MPO) activity in the area not at risk (ANAR), area at risk (AAR), and necrotic area (NEC) expressed as units/100 mg tissue wet weight in hearts from the main five treatment groups. *, P < 0.05; **, P < 0.01 vs. the vehicle-treated rabbits.

Figure 6

Representative recordings of the relaxation elicited by the endothelium-dependent vasodilator, acetylcholine (ACh), and the endothelium-independent vasodilator, acidified nitrite (NaNO₂), in U-46619 precontracted coronary artery rings isolated from sham MI rabbit (control) or from MI/R rabbits that had received different treatments. The arrows indicate addition of U-46619 (50 nM); dots on top indicate addition of ACh (0.001–10 μM) or NaNO₂ (0.1–100 μM).