The effects of phosphoramidon and thiorphan on production and metabolism of endothelin in guinea pig tracheal epithelial cell culture

Objective To observe the effects of endothelin converting enzyme (ECE) and neutral endopeptidase (NEP) on the conversion and degradation of endothelins in guinea pig tracheal epithelial cell in cultrue with a dual inhibitor of NEP and ECE, the phosphoramidon, and a selective inhibitor of NEP, the thiorphan. Methods The trachea of Hartley guinea pig was harvested under sterile condition. The epithelial cells were removed from the mucosal surface with cell scraper and seeded at a concentration of 5×10 5 cells/well in 24 well culture plate with DMEM/F12 and cultured at 37 °C in an atmosphere containing 5% CO 2. The cells reached confluency after 7 days. Then the cells were incubated for 10h with phosphoramidon or thiorphan respectively at concentration 0.1mmol/L. The supernatants were then collected and the concentrations of immunoreactive ET(ir ET) were measured by RIA.Results Comparison of the concentrations of ir ET between the control group (58.51±14.29)pg/mg protein and phosphoramidon group (40.43 ±15.37)pg/mg protein showed that phosphoramidon inhibited the release of ir ET( P =0.0288) by decreasing the formation of ET through inhibiting ECE. In contrast, thiorphan induced the increase of concentration of ir ET significantly (88.51±19.98)pg/mg protein, ( P =0.00387) by blocking the degradation of ET. Conclusion It is suggested that the ET is released and degraded by tracheal epithelial cell via ECE and NEP pathways. In prospective, ECE inhibitor may become a new path way in treat ment of bronchial asthma. (Shanghai Med J, 1999,22∶677 680)