Role of nitric oxide in mediating cardiovascular alterations accompanying heart failure in rats

Abstract

The present study was designed to evaluate the role of endothelial NO in the hemodynamics and vascular changes that occur in heart failure following myocardial infarction in rats. Left ventricular systolic pressure (LVSP), mean blood pressure (MBP), aortic morphology (media thickness) and reactivity were evaluated in rats with coronary artery ligation (heart failure, HF) or sham operation (SO) untreated or treated for four weeks with either a low dose of NG-nitro-L-arginine methyl ester (L-NAME, 6 mg·kg-1·day-1) or L-arginine (1.5 g·kg-1·day-1). In rats with HF LVSP (HF = 111 ± 8 mmHg; SO = 143 ± 6 mmHg, p < 0.05), MBP (HF = 98 ± 8 mmHg; SO = 127 ± 6 mmHg, p < 0.05) and aortic media thickness (HF = 68 ± 6 µm; SO = 75 ± 2 µm, p < 0.05) were significantly reduced. The contractile response to phenylephrine and the endothelium-independent relaxation to sodium nitroprusside were similar in HF and SO aortas, but the sensitivity (pD2) to acetylcholine (HF = 7.5 ± 0.06; SO = 7.1 ± 0.08, p < 0.05) was significantly increased in HF aortas, indicating an enhanced basal NO release. Treatment with L-NAME (LN) reversed the effects of HF on LVSP (HF-LN = 143 ± 9 mmHg, p < 0.05 vs. HF), MBP (HF-LN = 128 ± 8 mmHg, p < 0.05 vs. HF), sensitivity to acetylcholine (HF-LN = 6.9 ± 0.10, p < 0.05 vs. HF) and aortic media thickness (HF-LN = 79 ± 2 µm, p < 0.05 vs. HF), without changing these parameters in SO rats. L-NAME also selectively increased the maximal response to phenylephrine in HF aortas (HF-LN = 2.4 ± 0.20 g; HF = 1.6 ± 0.17 g, p < 0.05). L-arginine (LA) did not change the effects of HF on LSVP, MBP or aortic media thickness, but it reduced the sensitivity to phenylephrine in aortas from SO rats (SO-LA = 6.5 ± 0.12; SO = 7.0 ± 0.09, p < 0.05). Taken together, these results suggest an important role for endothelial NO in mediating the reduced vascular growth, myocardial dysfunction and hypotension in rats with HF.Key words: nitric oxide, myocardial infarction, heart failure, vascular reactivity.