Cardiac noradrenergic nerve terminal abnormalities in dogs with experimental congestive heart failure

We have shown previously that norepinephrine (NE) uptake activity is reduced in the failing right ventricle of animals with right heart failure (RHF) produced by tricuspid avulsion and progressive pulmonary constriction. However, it is unknown whether this defect in neuronal NE uptake is related to reduction of noradrenergic nerve terminals or whether these changes also occur in animals with left heart failure (LHF). It is also unknown whether increased NE release in heart failure contributes to the noradrenergic nerve abnormalities.

We measured myocardial NE content. NE uptake function, and noradrenergic nerve profiles in dogs with either RHF or LHF induced by rapid ventricular pacing. NE uptake activity was measured using [3H]NE, and noradrenergic nerve profiles were visualized by glyoxylic acid (SPG)-induced histofluorescence and tyrosine hydroxylase immunocytochemical staining. To study the effects of excess NE, we exposed normal dogs to 8 weeks of chronic NE infusion using subcutaneous osmotic minipumps. RHF and LHF animals exhibited reduced myocardial contractile function and congestive heart failure, as evidence by reduced cardiac output and elevated right atrial pressure. However, unlike that in LHF, left atrial pressure was not increased in RHF. The animals also showed an increase in plasma NE and a decrease in cardiac NE. In addition, SPG-induced histofluorescence correlated significantly with NE uptake activity (r = .712, P < .001) and tyrosine hydroxylase immunoreactive profiles (r = .569, P < .001) in the right ventricles of RHF dogs and in both ventricles of LHF dogs. The numbers of catecholaminergic profiles and tyrosine hydroxylase profiles significantly correlated with cardiac filling pressures. Chronic infusion of NE decreased heart rate in normal dogs but had no effect on either mean aortic pressure or left atrial pressure; like heart failure, it resulted in significant decreases in myocardial NE uptake activity and numbers of SPG-induced catecholaminergic histofluorescence and immunoreactive tyrosine hydroxylase profiles.

Myocardial NE uptake activity was reduced only in the failing ventricles with elevated filling pressure in RHF and LHF. These changes probably were caused by loss of noradrenergic nerve terminals in the failing ventricles, as evidenced by the reductions of catecholaminergic histofluorescence and tyrosine hydroxylase immunostained profiles. Furthermore, since similar reductions of myocardial NE uptake and noradrenergic nerve profiles could be produced by chronic NE infusion in normal dogs, elevated NE levels may play a role in the development of cardiac noradrenergic nerve abnormalities in congestive heart failure.