The effect of endothelin-1 on lipopolysaccharide-induced cyclooxygenase 2 expression in association with prostaglandin E2

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We demonstrated previously that endothelin-1 (10(-14) to 10(-8) M) promotes lipopolysaccharide-induced cyclooxygenase 2 expression and prostaglandin E(2) production through endothelin ET(B) receptors effects which are up-regulated by lipopolysaccharide. In the present study, we confirmed these findings and showed that prostaglandin E(2) (10(-6) to 10(-5) M) inhibited the lipopolysaccharide plus endothelin-1-induced cyclooxygenase 2 expression more profoundly as compared to its inhibition of the lipopolysaccharide-induced cyclooxygenase 2 expression. The endothelin ET(B) receptor selective antagonist, N-cis-2, 6-dimethylpiperidino-carbonyl-L-gamma-methyl-leucyl-D-L-methoxy carbon yl-tryptophanyl-D-norleucine (BQ788), partly inhibited this suppression. Interestingly, the expression of endothelin ET(B) receptors in macrophages was increased by lipopolysaccharide plus prostaglandin E(2) (10(-8) to 10(-5) M) about 1.6-fold compared with that evoked by lipopolysaccharide stimulation alone. We also showed that treatment with endothelin-1 at 10(-14) M (15 min) elevated an intracellular cyclic AMP concentration in macrophages stimulated by lipopolysaccharide or lipopolysaccharide plus prostaglandin E(2) (10(-6) M) for 6 h, and the elevation in the latter cells was more pronounced. These results suggested that endothelin-1 shows an opposite modulation of lipopolysaccharide-induced cyclooxygenase 2 expression in macrophages through endothelin ET(B) receptors, depending on the level of extracellular prostaglandin E(2), and the changes of intracellular cyclic AMP by endothelin-1 may be involved in this mechanism.

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