DELAYED RELEASE OF PROSTAGLANDINS FROM ARACHIDONIC-ACID AND KINETIC CHANGES IN PROSTAGLANDIN-H SYNTHASE ACTIVITY ON THE INDUCTION OF PROSTAGLANDIN-H SYNTHASE-2 AFTER LIPOPOLYSACCHARIDE-TREATMENT OF RAW264.7 MACROPHAGE-LIKE CELLS

In a mouse macrophage-like cell line, RAW264.7, arachidonic acid was c leaved within 30 min of lipopolysaccharide (LPS)-treatment, However, p rostaglandin (PG) synthesis did not accompany this cleavage, being del ayed by 4h, although significant PGH synthase (PGHS) activity was dete cted in the lysate of LPS-nontreated cells. The K-m value of this basa l PGHS activity toward arachidonic acid was more than one hundred-fold higher than that for the lysate of cells treated with LPS for 4h. Cha nges in the sensitivity of the PGHS activity to nonsteroidal antiinfla mmatory drugs after LPS-treatment also suggested induction of PGHS wit h different properties from that in the case of basal PGHS. The concom itant increase in PGH synthase (PGI-IS) activity with the induction of PGHS-2 protein after LPS-treatment suggested a contribution by PGHS-2 to the delayed synthesis of PGs in LPS-treated macrophage cells. As f or PGHS in the control cells without LPS-treatment, a different K-m va lue from that of PGHS-1 and the lack of cross-reactivity to anti-PGHS- 1 antibodies suggested that this basal PGHS was different from the typ ical PGHS-1. The lower affinity of this enzyme for arachidonic acid mi ght be the reason for the failure to release PGs by the cells without LPS-treatment.