The Inducible Nitric Oxide Synthase Is Impaired by Thrombin in Vascular Smooth Muscle Cells

The present study investigated whether or not thrombin may affect the induction of nitric oxide (NO) synthase caused by interleukin-1β in cultured smooth muscle cells (SMCs) from the rat aorta. The release of nitrite, an oxidation product of NO, from interleukin-1β-activated SMCs was inhibited by thrombin. The inhibitory effect of thrombin was prevented by hirudin, a thrombin inhibitor, and required the presence of thrombin during the induction period. Under bioassay conditions, the perfusate from interleukin-1β-activated SMCs relaxed endothelium-denuded rat aortic rings precontracted with phenylephrine. The perfusate from untreated SMCs or cells exposed to thrombin alone or to interleukin-1β in combination with thrombin relaxed only minimally the detector blood vessel. These observations demonstrate that thrombin inhibits the production of NO by the inducible NO synthase in cultured vascular SMCs.