ENDOTHELIN-1 INHIBITS NITRIC-OXIDE SYNTHESIS IN VASCULAR SMOOTH-MUSCLE CELLS

We investigated the effects of endothelin-1 on nitric oxide synthesis in vascular smooth muscle cells. We measured the production of nitrite , a stable metabolite of nitric oxide, and the expression of inducible nitric oxide synthase mRNA and protein in cultured rat vascular smoot h muscle cells. Incubation of the cultures with interleukin-1 beta (10 ng/mL) for 24 hours caused a significant increase in nitrite producti on. Endothelin-1 significantly decreased the interleukin-1 beta-induce d nitrite production by vascular smooth muscle cells in a dose-depende nt manner (10(-11) to 10(-8) mol/L). Incubation with interleukin-1 bet a for 24 hours induced expression of inducible nitric oxide synthase m RNA and protein in vascular smooth muscle cells, whereas endothelin-1 showed a suppressive effect on their expressions. Addition of the endo thelin type A receptor antagonist BQ-485, but not the endothelin type B receptor antagonist BQ-788, dose-dependently inhibited the effect of endothelin-1. After protein kinase C activity was functionally deplet ed by treatment of cells with phorbol 12-myristate 13-acetate for 24 h ours, the effect of endothelin-1 was abolished. These results indicate that endothelin-1 acts on endothelin type A receptors and inhibits ni tric oxide synthesis in interleukin-1 beta-stimulated vascular smooth muscle cells at least partially through a protein kinase C-dependent p athway.