Differential Regulation of Cyclo-Oxygenase-1 and Cyclo-Oxygenase-2 Gene Expression by Lipopolysaccharide Treatment <i>in vivo</i> in the Rat

1. Prostaglandins are important regulatory mediators of cardiovascular and pulmonary functions which may become disordered in patients with sepsis. The mechanisms controlling their synthesis and release under these circumstances remain unclear. Cyclo-oxygenase (COX, prostaglandin G/H synthase) is a key enzyme in prostaglandin synthesis and has two isoforms (COX-1 and COX-2). COX-1 is constitutively expressed and is probably responsible for prostaglandin release under physiological conditions, whereas COX-2 is expressed at high levels upon induction. 2. We investigated the effect of lipopolysaccharide treatment in vivo on differential COX-1 and COX-2 mRNA expression in the rat. 3. The 2.8 kb COX-1 message was detected in all lungs and seven hearts of eight control rats. In lipopolysaccharide-treated animals, COX-1 expression was reduced by approximately 5-fold in lungs and 2-fold in hearts as quantified by densitometry. In parallel, a marked upregulation of COX-2 mRNA expression was observed. The 4.4 kb COX-2 transcript was absent or expressed at low level in control lungs and hearts, but was increased by approximately 7- and 12-fold in lipopolysaccharide-treated lungs and hearts respectively. Neither the down-regulation of COX-1 nor the upregulation of COX-2 mRNA induced by lipopolysaccharide was significantly affected by pretreatment with dexamethasone in lung and heart, although expression of inducible nitric oxide synthase, induced by lipopolysaccharide, was markedly inhibited in the same tissues. 4. The down-regulation of COX-1 and upregulation of COX-2 may contribute to the multi-organ failure seen in sepsis.