The febrile response to lipopolysaccharide is blocked in cyclooxygenase-2 −/−, but not in cyclooxygenase-1 −/− mice

Abstract

Various lines of evidence have implicated inducible cyclooxygenase-2 (COX-2) in fever production. Thus, its expression is selectively enhanced in brain after peripheral exogenous (e.g., lipopolysaccharide [LPS]) or endogenous (e.g., interleukin-1) pyrogen administration, while selective COX-2 inhibitors suppress the fever induced by these pyrogens. In this study, we assessed the febrile response to LPS of congenitally constitutive COX-1 (COX-1 −/−) and COX-2 (COX-2 −/−)-deficient C57BL/6J-derived mice. COX-1 +/− and COX-2 +/− mice were also evaluated; controls were wild-type C57BL/6J mice (Jackson Labs.). All the animals were pretrained daily for two weeks to the experimental procedures. LPS was injected intraperitoneally at 1 μg/mouse; pyrogen-free saline (PFS) was the vehicle and control solution. Core temperatures ( T cs) were recorded using thermocouples inserted 2 cm into the colon. The presence of the COX isoforms was determined in cerebral blood vessels immunocytochemically after the experiments, without knowledge of the functional results. The data showed that the wild-type, COX-1 +/−, and COX-1 −/− mice all responded to LPS with a 1°C rise in T c within 1 h; the fever gradually abated over the next 4 h. By contrast, COX-2 +/− and COX-2 −/− mice displayed no T c rise after LPS. PFS did not affect the T c of any animal. It would appear therefore that COX-2 is necessary for LPS-induced fever production.