SEGMENTAL VASCULAR-RESISTANCE IN ISOLATED PERFUSED RAT LUNGS - INFLUENCE OF VASOMOTOR TONE AND CYCLOOXYGENASE AND LIPOXYGENASE INHIBITION

We have determined the profile of pressures in isolated perfused lungs of adult rats and investigated the influence of vasomotor tone and cyclooxygenase and lipoxygenase inhibition on total and segmental vascular resistance. We isolated and blood-perfused lungs of 30 rats (480 +/- 21 g). Group 1 (n = 7) was untreated, group 2 (n = 8) was paralyzed with papaverine, group 3 (n = 11) was treated with indomethacin, and group 4 (n = 4) was treated with indomethacin and U60257, a putative lipoxygenase inhibitor. Blood flow was adjusted initially to raise pulmonary artery pressure to approximately 15 cm H2O and then held constant. Airway and left atrial pressures were held constant at 7 and 8 cm H2O, respectively (zone 3 conditions). In all lungs, we measured pressures in subpleural 20-50-mu-m-diameter arterioles and venules using the micropuncture servonull technique. Thus, the pulmonary circulation was partitioned into three segments: arteries, microvessels, and veins. In group 1 lungs, arteries presented the largest fractional resistance to flow at 46% of total resistance, with microvessels and veins contributing 34% and 20%, respectively. In group 2 lungs that had no vasomotor tone, total vascular resistance was approximately 27% lower than in group 1 lungs, mainly due to a lower resistance in veins. In indomethacin-treated lungs (group 3) and indomethacin and U60257-treated lungs (group 4), total and segmental vascular resistance was not significantly different from untreated lungs (group 1). We conclude that in isolated perfused rat lungs, arteries are the predominant site of resistance to blood flow. Veins exhibit some vasomotor tone that can be eliminated with papaverine, and cyclooxygenase and lipoxygenase inhibition does not alter the characteristic profile of vascular resistance.