Effect of fibrinogen on IL-1β induced nitric oxide synthesis by endothelial cells. Confluent HUVEC monolayers were exposed to IL-1β (10 ng/mL) with or without fibrinogen (10 μg/mL) for 1 hour. Medium was then collected, and NO production was measured as nitrite concentration in the medium using the Griess reaction. Acetylcholine (3 mM) was used as a positive control, and L-NAME (3 mM) was used to inhibit NO synthesis. The results shown are mean ± SD of 3 separate experiments.