Altered reactivity of pulmonary vessels in postobstructive pulmonary vasculopathy

Chronic ligation of one pulmonary artery results in pulmonary vascular remo deling and bronchial angiogenesis, collectively known as postobstructive pu lmonary vasculopathy (POPV). To investigate pulmonary vascular reactivity i n POPV, we ligated the left main pulmonary artery of guinea pigs and, after 1-10 mo, prepared explants by inflating lungs with agarose and sectioning them into similar to 1-mm-thick slices; we measured areas of pulmonary vess els and determined contractile responses to histamine and serotonin (5-HT) and relaxant responses to ACh and sodium nitroprusside. We found maximal co ntractions of arteries to 5-HT (24.4 +/- 2.6%) and of veins to histamine (5 3.9 +/- 4.7%) were significantly increased in POPV of 3-mo duration compare d with those of controls (16.8 +/- 1.5 and 40.8 +/- 5.0%, respectively). Re laxation of arteries with ACh was enhanced at 10 mo but not at 1 mo after l igation. Relaxation with sodium nitroprusside was increased in veins at 1 m o after ligation but was not altered in arteries. Morphometry revealed redu ced diameters of arteries and veins without increased medial thickness. Our data suggest that the enhanced contractile responses of pulmonary vessels to histamine and 5-HT in POPV were not a result of endothelial dysfunction or of structural alterations but might be caused by as-yet-undiscovered mec hanisms.