Abstract

The bronchomotor and cardiovascular effects of epinephrine, ephedrine, pseudoephedrine, isoproterenol, methoxyphenamine and isoprophenamine were compared in anesthetized dogs. Although all of these drugs were capable of dilating the bronchioles when injected directly into the bronchial artery, they were not selective bronchodilators when injected intravenously. The minimum effective intravenous dose for bronchodilatation always elicited systemic arterial hypertension or hypotension due to the following primary actions of each drug:

Isoproterenol (1 to 3 microgm. total) injected directly into the common carotid, vertebral, superior mesenteric and external iliac arteries caused vasodilatation. This action was the major cause for the systemic arterial hypotension. It masked the accompanying cardiac stimulation which was detected as increases in myocardial force of contraction and in pulmonary blood flow.

Methoxyphenamine and isoprophenamine caused systemic vasodilatation similar to that of isoproterenol, but much larger doses were required (0.5 to 1 mgm. total, i.a.). The accompanying effect on the heart was a depression of myocardial force of contraction.

Epinephrine caused vasoconstriction when injected into the various systemic arteries (1 to 3 microgm. total). The systemic hypertensive response following its intravenous injection is due both to vasoconstriction and to stimulation of myocardial force of contraction.

Ephedrine caused vasoconstriction in the various systemic arterial beds (0.5 to 1.0 mgm. total, i.a.) and stimulation or depression of myocardial force.

Pseudoephedrine was a weaker constrictor than ephedrine for the common carotid, external iliac and superior mesenteric arteries. Unlike ephedrine, pseudoephedrine caused vasodilatation in the area supplied by the vertebral artery. The stimulation and depression of myocardial contraction for both isomers were approximately equal.