INFLUENCE OF HYPOXIA AND SEROTONIN ON SMALL PULMONARY VESSELS

X-ray angiograms obtained from isolated perfused dog lungs were used t o measure changes in the internal diameter of small intraparenchymal p ulmonary arteries (150-1,600 mu m) and veins (200-1,000 mu m) in respo nse to hypoxia or intra-arterial serotonin [5-hydroxytryptamine (5-HT) ] infusion. The diameter changes in response to the two stimuli were m easured over a range of stimulus-induced increases (Delta Pa) in the t otal arteriovenous pressure drop. When the resulting Delta Pa was smal l, all arteries in the diameter range studied constricted in response to either stimuli. The maximum decrease in diameter was similar to 25% with hypoxia and 36% with 5-HT. However, when Delta Pa was large, art eries with a control diameter larger than similar to 800 mu m distende d with hypoxia. On the other hand, 5-HT constricted all the arteries i n the size range studied regardless of the resulting magnitude of Delt a Pa. Hypoxia caused a small (similar to 9%) constriction in all veins in the diameter range studied independent of diameter or the magnitud e of Delta Pa, whereas in the concentration range studied 5-HT had no significant influence on these veins. An analysis of the potential imp act of these vessels on total pulmonary vascular resistance suggested that although vessels in the size range studied contributed significan tly to the total response to these two stimuli, vessels smaller than t hose studied also made a major contribution to the total response.