Effects of acute heart failure and administration of ouabain on cardiac catecholamine uptake

Acute effects of digoxin on total systemic vascular resistance in congestive heart failure due to dilated cardiomyopathy: a hemodynamic-hormonal study

The effects of the digitalis glycosides on systemic vascular resistance (SVR) in patients with congestive heart failure (CHF) are controversial. Most investigators report a reduction in total SVR, an action that has been attributed primarily to withdrawal of elevated sympathetic tone. Direct proof of this hypothesis is lacking, however, and the roles played by the renin-angiotensin-aldosterone and vasopressin systems have not been fully explored. Moreover, in several studies of patients with CHF, SVR did not decrease after the administration of digitalis. To clarify these issues, the hemodynamic and hormonal effects of digoxin were correlated in 11 normotensive men in sinus rhythm with CHF due to dilated cardiomyopathy. Patients were evaluated at rest and during submaximal exercise before and 6 hours after the intravenous infusion of 1.0 mg of digoxin (mean serum concentration 1.7 ng/ml). With digoxin therapy, heart rate, pulmonary wedge pressure and right atrial pressure declined and cardiac output increased. Although vasopressin was unchanged, both plasma norepinephrine concentrations and plasma renin activity decreased, the reduction in norepinephrine correlating with the increase in cardiac output. Despite these hemodynamic and hormonal effects, there was no change in total SVR at rest or during exercise. It is concluded that the improvement in cardiac function with digoxin in this patient group was a result of the inotropic properties of the drug, without an associated reduction in impedance. The failure of total SVR to decrease despite decreases in plasma norepinephrine levels and plasma renin activity might be explained by concomitant digitalis-induced vasoconstriction, impaired ability of arterioles to dilate in CHF, or offsetting alterations in other vasoactive hormone systems.

Post-countershock arrhythmias in untreated and digitalized dogs

Recent studies suggest that countershock can stimulate cardiac autonomic nerves and that the resulting release of norepinephrine contributes to post-countershock (PCS) arrhythmias. β-Adrenergic receptor blocking agents, reserpine, cocaine, and cardiac-denervated preparations were used to evaluate this hypothesis in dogs under pentobarbital anesthesia. The suitability of the dog as an experimental system was examined. In the normal dog, the duration of PCS arrhythmia caused by a countershock of given energy was increased 100% by ouabain (0.05 mg/kg iv). In both normal dogs and dogs given ouabain (0.05 mg/kg iv), dichloroisoproterenol, pronethalol, and propranolol reduced the duration of PCS arrhythmia; reserpine, a norepinephrine depletor, reduced the duration of PCS arrhythmia; cocaine, a norepinephrine-uptake inhibitor possessing antiarrhythmic properties, increased the duration of PCS arrhythmia; denervation of the heart reduced the duration of PCS arrhythmia. Ouabain (0.05 mg/kg iv) reduced the duration of PCS arrhythmia in dogs with denervated hearts. These findings indicate that PCS arrhythmia in dogs is norepinephrine dependent. Evidence indicated that ouabain has an anti-adrenergic action on the heart also is presented.