POTENT INHIBITION OF INDUCIBLE NITRIC-OXIDE SYNTHASE BY GELDANAMYCIN,A TYROSINE KINASE INHIBITOR, IN ENDOTHELIAL, SMOOTH-MUSCLE CELLS, ANDIN RAT AORTA

We have examined whether specific protein tyrosine kinase (PTK) inhibi tors (genistein, tyrphostin, or geldanamycin) prevent nitric oxide (NO .) production in rat smooth muscle cells (SMC), in murine brain endoth elial cells (MBE), and in isolated rat aortas treated with endotoxin ( LPS) and/or cytokines, Tyrphostin failed to inhibit either the release of nitrite in both endothelial and smooth muscle cells or vascular hy poreactivity in rat aorta, caused by immunostimulants, Genistein decre ased nitrite production in MBE only at high concentration but had no e ffect on nitrite production in SMC and on the hypocontractility in aor tic rings. In contrast, low concentrations of geldanamycin abolished t he release of nitrite in MBE and in SMC treated with endotoxin and/or cytokines, Geldanamycin inhibited also the hypocontractility to phenyl ephrine in aortic rings treated with LPS or interleukin-1, This inhibi tor failed to inhibit the release of nitrite and the vascular hyporeac tivity once nitric oxide synthase (NOS) was induced by immunostimulant s whereas methyl-L-arginine, an inhibitor of NOS, had significant effe cts. These data suggest that LPS- and cytokines-induced NO. production initiate a common signaling pathway involving a PTK that is inhibited by geldanamycin but not or slightly by tyrphostin or genistein at a p oint that precedes the induction of NOS. (C) 1997 Federation of Europe an Biochemical Societies.