Nitric oxide enhances PGI2production by human pulmonary artery smooth muscle cells

Abstract To evaluate the effect of exogenous nitric oxide (NO) and endogenous NO on the production of prostacyclin (PGI 2 ) by cultured human pulmonary artery smooth muscle cells (HPASMC) treated with lipopolysaccharide (LPS), interleukin-1 β (IL-1 β ), tumor necrosis factor α (TNF α ) or interferon γ (IFN γ ), HPASMC were treated with LPS and cytokines together with or without sodium nitroprusside (SNP), NO donor, N G -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 PGI 2 by radioimmunoassay. The incubation of HPASMC with various concentrations of LPS, IL-1 β or TNF α for 24 h caused a significant increase in nitrite release and PGI 2 production. However, IFN γ slightly increased the release of nitrite and had little effect on PGI 2 production. Although the incubation of these cells for 24 h with SNP did not cause a significant increase in PGI 2 production, the incubation of HPASMC with SNP and 10 μg/ml LPS, or with SNP and 100 U/ml IL-1 β further increase PGI 2 production and this enhancement was closely related to the concentration of SNP. However, stimulatory effect of SNP on PGI 2 production was not found in TNF α - and IFN γ - treated HPASMC. Addition of L-NMMA to a medium containing LPS or IL-1 β reduced nitrite release and attenuated the stimulatory effect of those agents on PGI 2 production. MeB significantly suppressed the production of PGI 2 by HPASMC treated with or without LPS or IL-1 β . The addition of SNP partly reversed the inhibitory effect of MeB on PGI 2 production by HPASMC. These experimental results suggest that NO might stimulate PGI 2 production by HPASMC. Exogenous NO together with endogenous NO induced by LPS or cytokines from smooth muscle cells might synergetically enhance PGI 2 production by these cells, possibly in clinical disorders such as sepsis and acute respiratory distress syndrome.