Thrombin prevents the expression of inducible nitric oxide synthase in vascular smooth muscle cells by a...

Proteolytically active forms of thrombin ( alpha- and gamma-thrombin) and thrombin receptor peptides inhibited the release of nitrite, a stable endproduct of nitric oxide, evoked by interleukin-1 beta (IL-1 beta ) in cultured vascular smooth muscle cells while proteolytically inactive forms [D-Phe-Pro-Arg chloromethyl ketone-alpha-thrombin (PPACK-alpha-thrombin) and diisopropylphosphoryl-alpha-thrombin (DIP-alpha-thrombin)] had either no or only minimal inhibitory effects. Under bioassay conditions, perfusates from columns containing IL-1 beta-activated vascular smooth muscle cells or cells treated with IL-1 beta plus PPACK-alpha-thrombin relaxed detector blood vessels. These relaxations were abolished by the inhibitor of nitric oxide synthesis, NG-nitro-L-arginine. No relaxations were obtained with untreated cells or IL-1 beta-treated cells in the presence of alpha-thrombin. The expression of inducible nitric oxide synthase mRNA and protein in vascular smooth muscle cells by IL-1 beta was impaired by alpha-thrombin. These results demonstrate that thrombin regulates the expression of the inducible nitric oxide synthase at a transcriptional level via the proteolytic activation of the thrombin receptor in vascular smooth muscle cells.