Absence of relation between the expression of cyclooxygenase isoforms and the synthesis of prostaglandin E₂ in resident and thioglycollate- elicited macrophages in rats

Macrophages exudating into inflammatory sites (thioglycollate-elicited macrophages, TGM) have a diminished ability to synthesize prostaglandins (PG) as compared with resident peritoneal macrophages (RM). Constitutive expression of cyclooxygenase-1 (COX-1) was lower in TGM than in RM but the releasability of arachidonic acid was not significantly different. Thus, the differences in expression of COX-1 were primarily responsible for the abilities of TGM and RM to synthesize PGE₂ upon calcium ionophore (CaI) stimulation. COX-1 expression in RM and TGM was also correlated with their ability to synthesize PGE₂ from exogenously added arachidonic acid. When exposed to lipopolysaccharide (LPS), the induction of COX-2 and the enhancement of PGE₂ synthesis upon CaI were much lower in TGM as compared with RM; the releasability of arachidonic acid upon CaI stimulation was relatively unchanged in RM but was reduced in TGM. Thus, in TGM as compared with RM, a lower level of COX-1 expression and a lower level of COX-2 induction, and the reduction of arachidonate releasability by LPS exposure, are mainly responsible for lower PGE₂ synthestic ability upon CaI stimulation. However, the different COX-2 induction by LPS in RM and TGM was not reflected in their increase in the ability to synthesize PGE₂ from exogenously added arachidonic acid.