Effect of adrenergic blockade on hypoxia-induced pulmonary vasoconstriction in awake dogs

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Abstract
Six awake dogs with chronically implanted intravascular catheters (pulmonary artery, left atrium, aorta) and electromagnetic flow probe (pulmonary blood flow, Q) were exposed to 45 min. of acute hypoxia (PIO2 = 75 mm Hg) before (control) and after alpha adrenergic (phenoxybenzamine) or beta adrenergic blockade (propranolol). Arterial O2 tensions were 85 mm Hg during hypoxia. Intravascular pressures, pulmonary vascular resistance (PVR), O2 consumption, CO2 production, alveolar and arterial gas tensions, and pH were studied. There were no significant differences between the control and phenoxybenzamine groups; in particular, the rise in PVR during hypoxia (50%) was unaltered by phenoxybenzamine. The propranolol group differed from control by lacking the hypoxia-induced rise in Q, by having a more pronounced rise in pulmonary artery pressure, and therefore an even more marked rise in PVR (95%). Phenoxybenzamine does not block hypoxia induced pulmonary vasoconstriction, but that propranolol blockade accentuates it.