Regular ArticleNitric oxide enhances PGI2production by human pulmonary artery smooth muscle cells

To evaluate the effect of exogenous nitric oxide (NO) and endogenous NO on the production of prostacyclin (PGI2) by cultured human pulmonary artery smooth muscle cells (HPASMC) treated with lipopolysaccharide (LPS), interleukin-1β(IL-1β), tumor necrosis factor α (TNFα) or interferon γ (IFNγ), HPASMC were treated with LPS and cytokines together with or without sodium nitroprusside (SNP), NO donor, NG-monomethyl-L-arginine (L-NMMA), NO synthetase inhibitor, and methylene blue (MeB), an inhibitor of the soluble guanylate cyclase. After incubation for 24 h, the postculture media were collected for the assay of nitrite by chemiluminescence method and the assay of PGI2by radioimmunoassay. The incubation of HPASMC with various concentrations of LPS, IL-1βor TNFαfor 24 h caused a significant increase in nitrite release and PGI2production. However, IFNγslightly increased the release of nitrite and had little effect on PGI2production. Although the incubation of these cells for 24 h with SNP did not cause a significant increase in PGI2production, the incubation of HPASMC with SNP and 10 μg/ml LPS, or with SNP and 100 U/ml IL-1βfurther increase PGI2production and this enhancement was closely related to the concentration of SNP. However, stimulatory effect of SNP on PGI2production was not found in TNFα- and IFNγ- treated HPASMC. Addition of L-NMMA to a medium containing LPS or IL-1βreduced nitrite release and attenuated the stimulatory effect of those agents on PGI2production. MeB significantly suppressed the production of PGI2by HPASMC treated with or without LPS or IL-1β. The addition of SNP partly reversed the inhibitory effect of MeB on PGI2production by HPASMC. These experimental results suggest that NO might stimulate PGI2production by HPASMC. Exogenous NO together with endogenous NO induced by LPS or cytokines from smooth muscle cells might synergetically enhance PGI2production by these cells, possibly in clinical disorders such as sepsis and acute respiratory distress syndrome.