The Genesis of the Initial Blood Pressure Peak Following iv Administration of Certain Catecholamines

The blood pressure changes in response to injection of certain sympathomimetic amines, epinephrine, norepinephrine and isoproterenol have been described many times, yet the genesis of the initial blood pressure peak has not been adequately explained. Measurements of cardiac contractile force, ascending aortic blood flow and heart rate in open chest dogs made during the iv injection of graded doses of epinephrine, norepinephrine and isoproterenol demonstrated that these parameters increased simultaneously with the initial blood pressure peaks. Total peripheral vascular resistance was not increased during the initial blood pressure peak produced by the beta adrenergic agonists. Administration of propranolol (1 mg/kg) blocked this initial blood pressure peak response while phenoxy-benzamine (1 mg/kg) did not. The latency period between injection of the beta adrenergic agonists and the appearance of the first rise in blood pressure was lengthened to about the same values observed for phenylephrine and angiotensin. Results from these experiments indicate that the initial blood pressure peak in response to iv injection of certain doses of epinephrine, norepinephrine and isoproterenol is due directly to beta adrenergic cardiac stimulation and an increase in aortic blood flow.