Downregulation of endothelial constitutive nitric oxide synthase expression by lipopolysaccharide

Lipopolysaccharide (LPS), a causal agent of sepsis, has been shown to induce systemic nitric oxide (NO) synthesis through complex mechanisms. However, the effect of LPS on endothelial cells is incompletely understood. To investigate the mechanism by which LPS influences the release of NO from endothelial cells, the effect of this compound on endothelial constitutive nitric oxide synthase (ecNOS) was studied in cultured bovine coronary venular endothelial cells. Western and Northern analyses showed that LPS decreased ecNOS expression at the protein and mRNA levels in a time-dependent and dose-responsive manner. Concurrent treatment of the endothelial cells with LPS and a transcription inhibitor, actinomycin D, resulted in decreased ecNOS mRNA within 8 hours. In contrast, treatment with actinomycin D had only a relatively insignificant effect on the ecNOS transcript level. This result suggests that the reduction of ecNOS by LPS resulted from an increased degradation rate of its transcript.