Effects of inhibitors of the activity of cyclo-oxygenase-2 on the hypotension and multiple organ dysfunction caused by endotoxin: a comparison with dexamethasone.

1. Endotoxaemia is associated with the expression of the inducible isoform of cyclo-oxygenase, cyclo-oxygenase-2 (COX-2), and an overproduction of arachidonic acid (AA) metabolites. The role of the AA metabolites generated by COX-2 in the circulatory failure and multiple organ dysfunction caused by endotoxin is unclear. Dexamethasone prevents the expression of COX-2 and exerts beneficial effects in animal models of shock. 2. Here we compare the effects of two inhibitors of COX-2 activity, namely NS-398 (5 mg kg(-1), i.p., n=7) and SC-58635 (3 mg kg(-1), i.p., n=9) with those of dexamethasone (3 mg kg(-1), i.p., n=9) on the circulatory failure and organ dysfunction caused by lipopolysaccharide (LPS, E. coli, 6 mg kg(-1), i.v., n=11) in the rat. 3. Endotoxaemia for 6 h caused hypotension, acute renal dysfunction, hepatocellular injury, pancreatic injury and an increase in the plasma levels of 6-keto-PGF1alpha (indicator of the induction of COX-2) and nitrite/nitrate (indicator of the induction of iNOS). 4. Pretreatment of rats with dexamethasone attenuated the hypotension, the renal dysfunction, the hepatocellular and pancreatic injury and the induction of COX-2 and iNOS caused by LPS. In contrast, inhibition of COX-2 activity with SC-58635 or NS-398 neither attenuated the circulatory failure nor the multiple organ failure caused by endotoxin. 5. Thus, the prevention of the circulatory failure and the multiple organ injury/dysfunction caused by dexamethasone in the rat is not due to inhibition of the activity of COX-2. Our results suggest that an enhanced formation of eicosanoids by COX-2 does not contribute to the development of organ injury and/or dysfunction in rats with endotoxaemia.