SELECTIVE-INHIBITION OF CYCLOOXYGENASE-2 BY NS-398 IN ENDOTOXIN-SHOCKRATS IN-VIVO

Objective and Design: The role of cyclooxygenase (COX)-2 was examined using a rat endotoxin shock model and the potency and selectivity of N S-398, a COX-2 selective inhibitor in vitro, for COX-2 activity was ex amined in vivo. Material: Male Wistar rats (weighing 140-180 g) were u sed. Methods: Lipopolysaccharide (LPS, 1 mg/kg, i.v.) was administered to rats (LPS-treated rats) and expression of COX-I mRNA and COX-2 mRN A in the aorta and peripheral blood leukocytes was examined by RT-PCR. COX activity was assessed by measuring the plasma 6-keto prostaglandi n (PG) F-1 alpha, PGE(2) and thromboxane (TX) B-2 30 s after administr ation of arachidonic acid (AA, 3 mg/kg, i.v.). NS-398 (0.3-100 mg/kg, p.o.) or indomethacin (0.3-3 mg/kg, p.o.) was administered I h before the AA injection. Results: COX-2 mRNA was detectable in the aorta and peripheral blood leukocytes at least from 3 to 9 h after the LPS injec tion but not in non-LPS-treated rats. Plasma 6-keto PGF(1 alpha), PGE( 2) and TXB2 levels after AA injection into LPS-treated rats were signi ficantly enhanced compared to findings in non-LPS-treated rats. NS-398 showed significant inhibition of the increase in PGs in LPS-treated r ats, the ED50 values being 0.35 mg/kg for 6-keto PGF(1 alpha), 1.5 mg/ kg for PGE(2) and <0.3 mg/kg for TXB2. NS-398 even at 100 mg/kg did no t significantly suppress the increased PGs levels in non-LPS-treated r ats. In contrast, indomethacin significantly inhibited plasma PGs leve ls after AA injection into LPS-treated rats and non-LPS-treated rats. The ED50 values in LPS-treated rats, determined by 6-keto PGF(1 alpha) , PGE(2) and TXB2 production, were 1.0, 1.3 and 2.3 mg/kg and those in non-LPS-treated rats were 0.42, 0.24 and 0.93 mg/kg, respectively. Co nclusions: In a rat endotoxin shock model, expression of COX-2 plays a role in an increase in COX activity. NS-398 showed preferential inhib itory effects on COX-2 activity in vivo. This approach is useful to di rectly analyze the inhibitory activity of NSAIDs for COX-I and COX-2 i n vivo.