The inhibition of platelet aggregation by activated macrophages is blocked by dexamethasone.

The effect of dexamethasone on the ability of activated J774 macrophages to inhibit platelet aggregation was investigated. After 24h incubation with lipopolysaccharide and gamma-interferon, J774 cells generated large amounts of nitric oxide and inhibited platelet aggregation. Incubation of the cells with dexamethasone (0.01-10 microM) caused a concentration-dependent inhibition of both the NO2- production and the anti-aggregating activity of the cells. The inhibitory effect of dexamethasone was blocked by the glucocorticoid antagonist RU 38486. These data suggested that the protective effect of glucocorticoids in endotoxin-induced hypotension and their immunosuppressive action may both depend, at least in part, on the inhibition by these steroids of the induction of the nitric oxide synthase.