Contribution of Vasoactive Eicosanoids and Nitric Oxide Production to the Effect of Selective Cyclooxygenase-2 Inhibitor NS-398 on Endotoxin-Induced Hypotension in Rats

摘要

Our previous studies with the use of non-selective cyclooxygenase (COX) inhibitor, indomethacin, demonstrated that prostanoids produced during endotoxaemia increase inducible nitric oxide (NO) synthase (iNOS) protein expression and NO synthesis, and decrease cyctochrome P450 (CYP) 4A1 protein expression and CYP 4A activity. The results suggest that dual inhibition of iNOS and COX by indomethacin restores blood pressure presumably due to increased production of 20-hydroxyeicosatetraenoic acid (20-HETE) derived from CYP 4A in endotoxaemic rats. The present study examined whether increased levels of vasoconstrictor eicosanoids, 20-HETE, PGF2α and thromboxane A2 (TxA2), would contribute to the effect of selective COX-2 inhibition to prevent endotoxin-induced fall in blood pressure associated with an increase in the production of vasodilator prostanoids, PGI2 and PGE2 and NO synthesis. Mean arterial blood pressure fell by 31 mmHg and heart rate rose by 90 beats per min. in male Wistar rats treated with endotoxin (10 mg/kg, i.p.). The fall in mean arterial pressure and increase in heart rate were associated with increased levels of 6-keto-PGF1α, PGE2, TxB2, and nitrite in the serum, kidney, heart, thoracic aorta and/or superior mesenteric artery. Systemic and renal 20-HETE and PGF2α levels were also decreased in endotoxaemic rats. These effects of endotoxin were prevented by a selective COX-2 inhibitor, N-(2-cyclohexyloxy-4-nitrophenyl)-methansulphonamide (10 mg/kg, i.p.), given 1 hr after injection of endotoxin. These data suggest that an increase in 20-HETE and PGF2α levels associated with decreased production of PGI2, PGE2, and TxA2, and NO synthesis contributes to the effect of selective COX-2 inhibitor to prevent the hypotension during rat endotoxaemia.