Expression of prostaglandin H synthase-2 in endotoxic shock induced in rats

We investigated the expression of prostaglandin H synthase-2 in rats subjected to endotoxic shock. The prostaglandin H synthase activities were assessed by measuring the plasma prostaglandins (PGE2 and 6-keto-PGF1 alpha) after arachidonic acid administration (3 mg/kg, i.v.). The plasma prostaglandin concentrations increased immediately after administration of arachidonic acid, reached a peak at 30-60 seconds, and then rapidly decreased. Lipopolysaccharide (1 mg/kg, i.v.) also increased the plasma prostaglandin concentrations, reached a peak 1 hour after administration, and then gradually decreased to normal levels. The production of plasma prostaglandin, induced by administration of arachidonic acid, was markedly enhanced in the lipopolysaccharide-treated rats. A low dose of acetylsalicylic acid (3 mg/kg, i.v.) blocked the prostaglandin production in the nontreated rats but not in the lipopolysaccharide-treated rats. In the latter group of rats, a high dose of acetylsalicylic acid (30 mg/kg, i.v.), given 10 to 30 minutes before administration of arachidonic acid, completely blocked the prostaglandin production, but recovery of this production was seen with acetylsalicylic acid (30 mg/kg) treatment at 1 to 2 hours before administration of arachidonic acid. These data suggest that pretreatment with lipopolysaccharide enhances the prostaglandin production by forming newly synthesized prostaglandin H synthase. Immunoblots of the levels of enzyme protein from rat aorta endothelial cells were analyzed. The enzyme protein cross-reacting with antibody against prostaglandin H synthase-2 was increased by lipopolysaccharide treatment in endothelial cells, and was constitutively expressed in the stomach, kidney and liver, but not in the lung and the intestine. The induction of prostaglandin H synthase-2 by lipopolysaccharide treatment was observed only in endothelial cells. The enhancement of the prostaglandin production in lipopolysaccharide-treated rats was blocked by pretreatment with dexamethasone, prior to administration of lipopolysaccharide, this suppression is apparently the result of a decrease of the prostaglandin H synthase-2 protein in endothelial cells, as determined by Western blotting. The enhanced production of prostaglandin, induced by lipopolysaccharide, seems to be due to the in vivo expression of prostaglandin H synthase-2.