Failure to Show Supersensitivity to l-Epinephrine and l-Norepinephrine in the Chronic Denervated Heart in Unanesthetized Dogs

¹ From the Department of Physiology, University of Illinois College of Medicine, Chicago, Illinois and the Carter Physiology Laboratory, University of Texas Medical Branch, Galveston, Texas

In the unanesthetized chronic denervated heart dog graded i.v. doses of l-epinephrine have a different pattern of circulatory effects depending upon whether they are given by quick injection or by infusion. Quick injections of l-epinephrine occasionally caused heart rate decreases and b.p. decreases; with the infusions these effects became frequent. By comparison, l-norepinephrine invariably affected heart rate and b.p. increases. Further, l-norepinephrine was a better positive chronotropic agent than l-epinephrine by roughly 100% and the durations of the chronotropic and pressor effects were lengthened. Three of four of the denervated heart dogs did not become supersensitive to either agent by any criterion. In the fourth dog there was a slight and roughly equal chronotropic sensitization which was insignificant in extent and without marked differential as compared to other denervated structures. Thus the data, while not conclusive, does not lend support to any of the theories wherein one or the other of these agents is regarded as the chief sympathetic mediator.