THROMBIN TRIGGERS THE DE-NOVO EXPRESSION OF AN INDUCIBLE NO SYNTHASE IN PORCINE AORTIC-VALVE ENDOTHELIAL-CELLS

The nitric oxide (NO) production by porcine aortic valve endothelial c ells was estimated in cusps incubated at 37 degrees C by measuring the ir cyclic GMP content and the nitrite levels of the incubation medium. After a stabilization period, incubations for 5 min with acetylcholin e, bradykinin, ADP and bovine thrombin resulted in a receptor-mediated increase in cyclic GMP which could be blocked by EGTA, N-omega-nitro- L-arginine methyl ester (L-NAME) and N-G-monomethyl-L-arginine (L-NMMA ). Incubation with lipopolysaccharide (endotoxin) from E. coli 0111:B4 or bovine thrombin for 5 h, dose-dependently increased nitrite produc tion as well as cyclic GMP content. The elevated nitrite production wa s completely abolished in the presence of the protein synthesis inhibi tor cycloheximide, was reduced by more than 50% by dexamethasone but w as not affected by EGTA. L-NMMA dose-dependently reduced the increased nitrite production and cyclic GMP content. These results suggest that besides the presence of a constitutive NO synthase in porcine aortic valve endothelial cells thrombin, like lipopolysaccharide, triggers th e de novo expression of an inducible Ca2+-independent NO synthase.