EVIDENCE FOR MODULATION OF HYDROGEN PEROXIDE-INDUCED ENDOTHELIAL BARRIER DYSFUNCTION BY NITRIC-OXIDE IN-VITRO

Acute effects of the nitric oxide (NO) donors sodium nitroprusside and glyceryl trinitrate on hydrogen peroxide (H2O2)-induced increases in endothelial monolayer permeability to trypan blue-labelled bovine seru m albumin have been investigated in vitro. Exposure of bovine pulmonar y artery endothelial cell monolayers to 0.2 mM H2O2 for 20 min caused a significant increase in percentage trypan blue-labelled albumin tran sfer from the lumenal to the ablumenal compartment (basal 6.0 +/- 0.6 to 25.4 +/- 0.9%, n = 4, P < 0.0005). In separate experiments 100 mu M sodium nitroprusside significantly enhanced the effect of 0.2 mM H2O2 (from 7.4 +/- 1.4 to 11.9 +/- 1.5%, n = 9, P < 0.0001) but did not al ter albumin transfer in the absence of H2O2. This additive effect appe ared to be due to NO release from sodium nitroprusside, since nitrite concentration in the medium overlying cells treated with 100 mu M sodi um nitroprusside was 19.9 +/- 1.8 mu M (n = 12). Significantly less ni trite (3.5 +/- 0.5 mu M, n = 12, P < 0.0001) was found in the medium o verlying cells treated with 100 mu M glyceryl trinitrate, which in con trast to sodium nitroprusside, inhibited the permeability increase cau sed by H2O2 (from 15.6 +/- 3.3 to 13.8 +/- 3.1%, n = 6, P < 0.001). Fu rthermore 10 mu M sodium nitroprusside, which released comparable amou nt of nitrite (4.5 +/- 0.4 mu M, n = 6) to 100 mu M glyceryl trinitrat e, also inhibited the permeability increase caused by H2O2 (from 20.7 +/- 0.4 to 19.4 +/- 0.3%, n = 9, P < 0.01). We conclude that relativel y large amounts of NO released from 100 mu M sodium nitroprusside exac erbate the barrier dysfunction caused by H2O2, while lower amounts of NO give a small amount of cytoprotection.