COMPARATIVE EFFECTS OF A WIDE RANGE OF DOSES OF L-EPINEPHRINE AND OF L-NOREPINEPHRINE ON THE CONTRACTILE FORCE OF THE HEART IN SITU

¹ Department of Pharmacology, Tulane University School of Medicine, New Orleans, Louisiana

The positive inotropic effects of l-epinephrine and l-norepinephrine, as measured directly with the strain gauge arch, have been shown to be qualitatively and quantitatively similar over a wide range of doses. The positive inotropic effects of these two amines in vagotomized dogs under anesthesia were almost identical with those in intact, fully conscious animals.

In the anesthetized and vagotomized dogs, small doses of l-epinephrine and of l-norepinephrine had little effect on the heart rate, while large doses produced tachycardia. In unanesthetized and unpremedicated dogs, both amines produced a bradycardia which was more pronounced at the higher dose ranges. l-Norepinephrine usually slowed the heart to a greater extent than did l-epinephrine.

The effects of the two amines on the blood pressure were qualitatively different in most instances, the effects of l-epinephrine being characterized by a decrease in the diastolic pressure and an increase in the systolic pressure, the effects of l-norepinephrine being characterized by an increase in both the diastolic and the systolic pressures. In a few instances, the effects of these two amines on the blood pressure could not be distinguished from one another.

Each increase in the systolic blood pressure produced by either l-epinephrine or l-norepinephrine was associated with an increase in the force of ventricular contraction over a wide range of doses.