776-4 Intact cNOS-NO-cGMP Pathway in the Failing Human Heart

Abstract

Nitric oxide (NO) is a potent endothelium-derived relaxing factor which also may modulate cardiac myocyte inotropism and growth via increases in cGMP. While both the constitutive (cNOS) and inducible (iNOS)forms of nitric oxide synthase have been detected in mammalian hearts, the overall presence and activity of the cNOS-NO-cGMP pathway in the normal and failing human heart remains poorly defined. The present studies were designed to investigate the cNOS-NO-cGMP pathway in normal and failing human atrial and ventricular myocardium and to determine plasma NO and cGMP in the presence and absence of CHF. Myocardial tissue and plasma were obtained from five end-stage heart failure patients undergoing cardiac transplantation and five cardiac donors. Normal plasma NO and cGMP were also determined in normal humans without disease. cNOS production and localization were determined utilizing Northern blot analysis, in situ hybridization and immunohistochemistry with probes for endothelial-NOS and brain-NOS. Plasma and tissue NO were measured by nitrate determination utilizing chemiluminescence. Northern blot analysis and in situ demonstrated cNOS to be present and localized to atrial and ventricular myocytes in equal concentrations and distributions in normal and failing hearts. Tissue NO as determined by nitrate concentration was detectable and equal in normal and failing hearts while plasma NO concentration tended to be increased in CHF patients. Cardiac tissue cGMP paralleled tissue NO, although, plasma cGMP concentration was significantly increased in CHF patients compared with normal subjects. The present studies demonstrate that cNOS mRNA and cNOS protein are present in the normal human heart and this cNOS-NO-cGMP pathway is preserved in the failing human heart. These studies suggest that this paracrine and autocrine pathway may continue to function in the control of myocardial function in the failing human myocardium.