A Radiologic and Physiologic Investigation into Hypoxic Pulmonary Vasoconstriction in the Dog

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Abstract
We examined the site and mechanism of hypoxic vasoconstriction in a single lobe of the dog lung. In anesthetized dogs pulmonary arteriography in an exteriorized lung lobe showed vasoconstriction during hypoxia. The vasoconstriction was maximal in the smallest vessels studied (300-micrometer diameter), in which a 19% reduction in diameter was observed during hypoxia; no significant change in caliber occurred in vessels exceeding 2 mm in diameter. Reversal of the vascular response occurred upon withdrawal of the hypoxic stimulus. In a second study using the same model, saralasin acetate, a specific competitive antagonist of angiotensin II, failed to modify the constrictor response to hypoxia. It is concluded from these studies that the site of the increased pulmonary vascular resistance evoked by alveolar hypoxia is located predominantly in the small pulmonary arteries, and that angiotensin II plays no significant role in the mediation of the response.

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