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Objective: In search of an agent to attenuate the increased pulmonary vascular resistance after lung transplantation with extracorporeal circulation, we investigated contractions and relaxations of isolated porcine pulmonary arterial rings in organ chambers., Methods: Rings of arteries from three groups were studied. Rings from the heart-lung block were studied immediately after Euro-Collins flush (n = 6). Rings from the recipient's native (n = 5) and transplanted (n = 5) lung were studied after 3 h of right heart bypass following transplantation. The duration of cold ischemia of the transplanted lung was 3-4 h. Contractions to potassium chloride and phenylephrine were measured. In order to study relaxations, the rings were preconstricted with phenylephrine. Relaxations to acetylcholine, adenosine diphosphate and isoproterenol were determined in rings with endothelium, and relaxations to sodium nitroprusside in rings without endothelium., Results: Sodium nitroprusside induced complete relaxations (100%) in rings of arteries from all three groups. Relaxations to acetylcholine and adenosine diphosphate were comparable among the three groups, but relaxations to isoproterenol were significantly depressed in pulmonary artery rings from the transplanted lung, compared with those from the native lung., Conclusions: Lung transplantation with extracorporeal circulation is associated with depressed beta-receptor-mediated vasodilation, but the pulmonary vascular smooth muscle cell's ability to relax is not affected.