Nitric oxide gas decreases endothelin-1 mRNA in cultured pulmonary artery endothelial cells

Inhaled nitric oxide gas (iNO) vasodilates the pulmonary circulation. The effective "dose" of iNO for chronic treatment of pulmonary hypertension is unknown. Increased abundance of pulmonary mRNA for preproendothelin-1 (ppET-1) with its associated increase in endothelin-1 (ET-1) could contribute to the development of both clinical and experimental pulmonary hypertension. The benefit of iNO therapy may be from inhibition of ET-1 production. The present study was designed to compare the effects of two therapeutic concentrations of NO gas, 10 parts per million (p.p.m.) and 100 p.p.m. on the steady-state level of mRNA for ppET-1 and nitric oxide synthase (NOS III), in cultured bovine pulmonary artery endothelial cells. Uptake of NO gas was assessed by measurement of nitrite anions in the medium. The mRNA for ppET-1 and NOS III was determined by semiquantitative reverse-transcriptase polymerase chain reaction (RT-PCR). After 4 h exposure to 100 p.p.m. NO in air, nitrite anions levels were 1.6 microM in the endothelial cell media as opposed to 0.23 microM with 10 p.p.m. NO. The levels were 0.02 microM in control cells exposed to air alone. Exposure to 100 p.p.m. NO reduced the steady state levels of mRNA for ppET-1, but not NOSIII mRNA levels. By comparison 10 p.p.m. NO did not affect levels of either mRNA.