Effect of orciprenaline on hypoxic pulmonary vasoconstriction in dogs

The effect of orciprenaline on hypoxic pulmonary vasoconstriction and arterial oxygen tension (PaO2) was studied in 8 dogs by measuring the redistribution of blood flow in response to unilateral alveolar hypoxia. The distribution of blood flow was recorded continuously by measuring the radioactivity of the mixed expired gas from each lung during the continuous intravenous infusion of xenon-133. The hypoxic vasoconstrictor response was significantly depressed by an infusion of 1.0 micrograms/kg/min of orciprenaline but not by a dose of 0.1 micrograms/kg/min. PaO2 during unilateral hypoxia was significantly lower during the infusion of the high dose of orciprenaline than it was in the control periods before or after the infusion. A bolus dose of 0.5 mg significantly increased blood flow to a lung with established hypoxic vasoconstriction and also caused a significant reduction in PaO2. Since these effects were produced in the absence of airway pressure or pulmonary vascular pressure changes, it is concluded that orciprenaline may depress the hypoxic pulmonary vasoconstrictor response in dogs.