Comparative Study of Inotropic Effects of Catecholamines on Blood-perfused Canine Papillary Muscle

The relative inotropic potencies of isoproterenol, norepinephrine, epinephrine and phenylephrine were compared in the blood-perfused canine papillary muscle preparation. The muscle was perfused at a constant pressure of 100mm Hg at 38-39°C with arterial blood from a donor animal. The isometric tension developed by the papillary muscle and the positive inotropic effect of catecholamines were a function of the stimulus frequency. The potencies of the inotropic effect of catecholamines were compared at various stimulus frequencies from 90 to 240/min. Isoproterenol, norepinephrine and epinephrine, 0.001 to 0.1μg, caused reproducible positive inotropic effects lasting for from 2 to 5min, when the perfused blood flow of the muscles was from 3 to 5ml/min. Phenylephrine, 0.01 to 1μg, caused no inotropie effect. The order of potencies of inotropic effect of each amine was isoproterenol>norepinephrine>epinephrine>>phenylephrine. The dose ratio required to produce 100% increase in isometric tension was IS:NE:EP=1:3:6 at stimulus frequencies of 90 and 120/min. The ratio of the percentage increase produced by 0.03μg of each agent was roughly IS:NE:EP=3:2:1 and 5:3:1 at 90 and 120/min, respectively. Norepinephrine produced a distinctly stronger positive inotropic effect than did epinephrine and the differences between these amines were statistically significant.