A proposed mechanism for epinephrine potentiation by ganglionic blocking agents

¹ Department of Pharmacology, Marquette University School of Medicine, Milwaukee, Wisconsin

The blood pressure responses elicited by the injection of 1.0, 5.0, and 10.0 µg/kg of epinephrine were studied before and after blockade of autonomic nervous activity by either ganglionic blocking agents or by total spinal anesthesia. After blockade, blood pressure levels of 100, 130, and 160 mm Hg were maintained by infusion of epinephrine. The results of these studies showed that the pressor responses elicited were inversely related to the level of the maintained blood pressure and that the maximum attained blood pressures did not change markedly with the various maintained blood pressures. In the series of animals treated with ganglionic blocking agents, the maximum blood pressures were approximately the same before and after blockade but in the total spinal anesthetized animals these pressures were approximately 30 mm Hg lower after blockade. It was postulated from these results that autonomic blockade produces an apparent potentiation of epinephrine pressor response not by sensitization of the reacting structures but by lowering the level of catecholamines available to the receptor sites and shifting the dose-response curve to the left.