Abnormalities in vasomotor tone, including enhanced vasoconstriction at rest and diminished vasodilation in response to various stimuli, develop as a consequence of chronic
heart failure. This study was undertaken to evaluate whether a specific local mechanism, namely
endothelium-derived relaxing factor (EDRF) activity, might be impaired in an experimental model of chronic
heart failure. Segments of thoracic aorta (TA) and pulmonary artery (PA) were isolated from a group of rats that had hemodynamic evidence of
heart failure 10 weeks after
ligation of the left coronary artery (n = 25) and from a group of
sham-operated control rats (n = 18). Both endothelium-dependent and endothelium-independent vascular responses were assessed by exposing arterial segments to increasing concentrations of agonists. All studies were performed in the presence of 10 microM
indomethacin to avoid the influence of vasoactive
prostanoids. The dose-response curve for EDRF-mediated relaxation to
acetylcholine was shifted rightward in rats with
heart failure, and the concentrations of
acetylcholine required to achieve 50% maximal relaxation (EC50) were increased compared with those of control rats in both TA and PA segments. Additionally, the dose-response curve for relaxation to
ADP was shifted rightward with significantly increased EC50 in PA segments from rats with
heart failure. In contrast, EDRF-mediated relaxation to the
calcium ionophore A23187 was similar in the groups. Endothelium-independent relaxation to
nitroglycerin was slightly increased in TA but not PA segments in the
heart-failure group. Basal EDRF activity, as assessed by the increase in force after exposure to
hemoglobin, was diminished in PA segments from rats with
heart failure.(ABSTRACT TRUNCATED AT 250 WORDS)