Induction of prostaglandin H synthase-2 (COX-2) in mononuclear cells of rat carrageenin-induced pleurisy and inhibitory effects of a selective COX-2 inhibitor

Abstract

Recently, inducible prostaglandin H synthase-2 (cylooxygenase (COX)-2) was reported in cells in vitro, but there is no evidence on the presence of COX-2 in inflammatory sites. Rat pleurisy was induced by intrapleural injection of 0.2 ml of 2% ~.-carrageenin. The pleural exudate started to be accumulated from 1 hr and reached a plateau at 19 hr after carrageenin injection. The plasma exudation for 20 min into the pleural cavity, assessed by exudation of pontamine sky blue after intravenous injection, was rapidly increased up to 5 hr and declined gradually thereafter. The levels of 6-keto-prostaglandin (PG) Flot, PGE2 and thromboxane B2 in the pleural exudate were increased between 1 and 7 hr after carragecnin injection, having a peak at 1, 3-5, 3-7 hr, respectively. The plasma exudation and the exudate volume at 15 hrs were inhibited by aspirin. Using an immunoblot analysis, COX-2 was detected neither in the white cells in peripheral blood and in the pleural cells before carrageenin, but was dctected in the cells of the pleural exudate from 1 hr. The level was at maximum at 3-5 hr, being reduced thereafter, and was hardly detected at 19 hr. Mononuclear cells, not polymorphonuclear leukocytcs, in the pleural cxudatc produced COX-2. COX-1 was present at the same level in the white cells in pcripheral blood and in thc pleural cells before and after carrageenin injection. Messenger RNA of COX-2 was also expressed in thc cells of the exudate at 5 hr, as detected by a Northern hybridization analysis. Dexamethasonc (0.3-30 mg/kg, i.p., 2 hrs before carrageenin) suppressed the COX-2 induction at the dose of highcr than 3 mg/kg. The prostanoid levels in the pleural exudate were suppressed by 3 mg/kg of dexamethasonc. A new anti-inflammatory drug, NS-398 (N-[2-cyclohexyloxy-4-ni trophenyll methanesulfonamidc, Taisho Pharmaceut. Co.), inhibited COX-2 from sheep placenta at smaller doses than those for inhibition of COX-1 from sheep vesicular gland, whereas indomethacin inhibited COX-I at higher doses than those for COX-2 in vitro. The plasma exudation and the exudate volume at 5 hr in the carragcenin-induced pleurisy was suppressed by NS-398 (3 mg/kg, p.o.) at the same degree as by aspirin (100 mg/kg, p.o.). Only COX-l, not COX-2, was detected in the microsomal fraction of lung, stomach and kidney of the pleurisy rats and the non-pleurisy rats. Thus, selective COX-2 inhibitors may exert its anti-inflammatory actions without side effects on stomach and kidney.