Mechanism of Action of Norepinephrine in Hemorrhagic Shock

¹ From the Department of Physiology, Faculty of Medicine, University of Western Ontario, London, Canada

Twenty-nine dogs were subjected to a standardized hemorrhagic shock procedure, and various indices were measured in the succeeding 24 hours. During this period, 15 animals received intravenous l-norepinephrine, 0.2– 1.0 µg/kg/min. beginning immediately after the shock procedure. The survival rate of the control animals was 2/14, and of the treated 6/15. Norepinephrine infusion sustained the arterial pressure of the treated animals, not by increasing the peripheral resistance, but rather by maintaining the cardiac output. Since the decline in effective circulating plasma volume that occurred in the first 8 hours after the shock procedure was not prevented by norepinephrine, it is concluded that, in these doses, norepinephrine may exert its beneficial effect by a direct action on the heart. The increased oxygen consumption after the shock procedure in the norepinephrine-treated animals may have been due to a direct effect of the drug on metabolism.