Sympathetic Nervous System Sensitivity to Hemorrhagic Hypotension in the Subhuman Primate

The endogenous catecholamine response to hemorrhagic hypotension is poorly defined since most data have been derived from experiments in lower animal species. To clarify this situation we studied the plasma norepinephrine (NE) and epinephrine (Epi) responses to hemorrhagic hypotension in ten healthy male baboons (Papio anubis). After an overnight fast, animals were tranquilized with 100 mg of ketamine hydrochloride after which femoral artery and vein catheters were inserted. The animals then underwent phlebotomy of 20 ml/kg over 60 minutes with retransfusion of the autologous blood over the next 30 minutes. Plasma specimens for catecholamines were collected at 5, 15, 30, and 60 minutes during phlebotomy and again at 15 and 30 minutes during retransfusion. Plasma NE and Epi concentrations were measured by a radioenzymatic technique. Mean arterial blood pressure (MAP) decreased (p less than 0.01) and heart rate (HR) increased (p less than 0.01) within 15 minutes of phlebotomy, and these variables returned to baseline with retransfusion. Plasma NE and Epi levels increased (p less than 0.025) within 5 minutes of the onset of 'hemorrhage' and within 15 minutes plasma NE concentrations were 56% above baseline, whereas plasma Epi levels were six times greater than baseline. With retransfusion, plasma NE and Epi levels returned to baseline concentrations. We conclude: 1) in a primate species, the sympathetic nervous system responds rapidly to hemorrhage; 2) contrary to prior studies in rats, plasma NE increases as rapidly as Epi but not to the same degree; 3) plasma NE and Epi concentrations rapidly return to baseline levels with fluid resuscitation; and 4) there is little justification for the use of exogenous synthetic catecholamines in hemorrhagic hypotension where fluid resuscitation remains the treatment of choice.