The Neurogenic Vasoconstrictor Effect of Digitalis on Coronary Vascular Resistance

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Abstract
The coronary vasoconstrictor properties of digitals were evaluated in 61 anesthetized, openchest dogs after coronary sinus cannulation and under conditions of a constant heart rate (atrioventricular pacing) and near-constant blood pressure. The contribution of alpha adrenergic receptor stimulation to the digitalis-induced increase in coronary vascular resistance (CVR) was examined. With Na pentobarbital anesthesia (16 dogs), intravenous acetylstrophanthidin (0.5 mg) caused a significant (P3/min. The mean time to peak effect was 3 min, and to recovery was 21 min. Prior alpha adrenergic receptor blockade with phenoxybenzamine in 11 animals reduced (PP3/min). One-third the dose of intravenous digoxin (0.35 mg) produced a 9.5±1.0% increase in CVR (five additional dogs). Myocardial oxygen consumption did not change significantly in nine dogs after intravenous digoxin. In 10 additional dogs pretreated with phenoxy-benzamine and in 7 dogs pretreated with mecamylamine, the increase in CVR did not occur after 1.0 mg of intravenous digoxin. Thus there is a coronary vasoconstrictor effect of intravenous acetylstrophanthidin and digoxin, of rapid onset, which is mediated through alpha adrenergic receptor stimulation.