Aim: To study the interactions between prostacyclin and endothelium-derived nitric oxide in porcine pulmonary arteries.
Methods: Rings of 5th order of porcine pulmonary arteries were studied in vitro for the measurement of tension and the content in cyclic nucleotides.
Results: Prostacyclin, given exogenously, caused endothelium-potentiated relaxations (inhibition of phenylephrine contraction) that were inhibited by the inhibitors of the L-arginine nitric oxide pathway, oxyhemoglobin and N omega-nitro-L-arginine. These inhibitors did not affect the tension in rings without endothelium. Cyclic GMP-concentrations were not increased above basal concentrations in the presence of prostacyclin. Increases were seen with acetylcholine and sodium nitroprusside. Prostacyclin-stimulated cyclic AMP concentrations did not reach statistical significance compared to controls. The addition of 8-bromo-cyclic GMP to prostacyclin, however, increased the cyclic AMP content. The nitric oxide synthase inhibitor, nitro-L-arginine (NLA), reduced the prostacyclin-stimulated cyclic AMP content to basal level. Inhibition of cyclic GMP-inhibited cyclic AMP phosphodiesterase by 8-bromo-cyclic GMP or amrinone (a specific inhibitor of this enzyme) potentiated the prostacyclin-induced relaxations in rings without endothelium to a magnitude similar to that observed in rings with endothelium.
Conclusion: These data suggest that the augmentation by the endothelium of the prostacyclin-induced relaxation of porcine pulmonary arteries is secondary to the inhibition of cyclic GMP-inhibited cyclic AMP phosphodiesterase by basally released endothelium-derived nitric oxide.