The effects of a single i.v. injection or infusion of Aminorex (2-amino-5-phenyl-2-oxazoline-fumarate) on blood pressure, blood flow, and haemodynamic resistance of the pulmonary and femoral arteries were investigated in anaesthetized dogs and compared with those of Norepinephrine. The following results were obtained: 1. Aminorex (dose-range between 10 and 160 μg/kg i.v.) caused a transient increase in the mean blood pressure of the pulmonary artery and in the mean pulmonary perfusion pressure (Part. pulm. - Pleft atrium). At the same time the pulmonary blood flow fell by 10-20%. A dose-dependent increase in the vascular resistance of the pulmonary vessels was observed in all experiments. The effects lasted for 20 to 60 min, according to the dose. Isoproterenol (1,0 μg/kg i.v.) led to a fall in the pulmonary vascular resistance and abolished the resistance increase following the Aminorex-administration. 2. An i.v. infusion of Aminorex (dose-range between 5 and 50 μg/kg/min) led to an increase in pulmonary blood pressure and vascular resistance. At the same time a slight decrease in heart rate and pulmonary blood flow was obtained. These pulmonary haemodynamic changes reached their maximum 15 min after the onset of the infusion and remained constant during the whole period of an infusion lasting 40 min. After discontinuing the infusion the pressure and resistance values returned only partially to the preinfusion values. 3. An infusion of 10 μg/kg/min Aminorex led to an increase in the blood pressure of the systemic circulation and in the total peripheral vascular resistance. Both changes were less marked when compared with the simultaneously occurring effects on the pulmonary haemodynamics. At the same time the blood flow in the femoral artery was diminished to a greater degree than in the pulmonary artery. As a result of the observed flow- and pressure changes in the pulmonary and femoral arteries the influence of an Aminorex-infusion on the haemodynamic resistance of both vessels was identical with regard to the time course and the intensity of the observed effects. 4. Pretreatment with Phentolamine abolished the effects of an infusion of 10 μg/kg/min Aminorex on pulmonary blood pressure and vascular resistance, whereas pretreatment with Propranolol enhanced these effects. 5. Following an i.v. infusion of 0.5 μg/kg/mm Norepinephrine pulmonary blood pressure and vascular resistance rose only transiently, whereas the pulmonary blood flow decreased at the same time, due to an initial fall in heart rate. These initial changes did not last in spite of a continued Norepinephrine infusion. 6. The effects of Norepinephrine on the systemic blood pressure were more pronounced than those on the pulmonary blood pressure. As a consequence, the increase in the work done by the left ventricle was greater than the increase in the work done by the right ventricle. In contrast, the increase in blood pressure and vascular resistance caused by Aminorex was more pronounced in the pulmonary circulation and therefore the right ventricular work increased more than the left ventricular work. © 1969 Springer-Verlag.
