BW-A137C

Inhibition of constitutive nitric oxide (NO) synthases by administration of N(G)-nitro-L-arginine methyl ester (L-NAME) during abdominal laparotomy provokes extensive vascular leakage in the rat gastrointestinal tract, assessed by the extravasation of [125I]human serum albumin. In the present study, the role of vasoactive or neutrophil-derived pro-inflammatory mediators in this process has been investigated. Administration of the thromboxane synthase inhibitor, 1-benzyl-imidazole (BZI, 25-50 mg kg(-1), s.c.), the platelet-activating factor (PAF) receptor antagonist, 3-[4-(2-chlorophenyl)-9-methyl-6H-thienol-[3,2-f][1,2,4]-triazolo- [4, 3-a][1,4]-diazepine-2-yl]-1-(4-morpholynil)-1-propionate (WEB 2086; 0.5-1 mg kg(-1), s.c.), the 5-lipoxygenase synthase inhibitor, N-(4-benzyloxybenzyl)-acetohydroxamic acid (BW A137C; 4-20 mg kg(-1), s.c.) or the vasopressin pressor receptor antagonist ([Mca(1), Tyr(Me)(2),Arg(8)]vasopressin/Manning peptide; 0.01-0.2 microg kg(-1), s.c.) dose-dependently reduced the intestinal plasma leakage provoked by L-NAME (5 mg kg(-1), s.c.), following a 5-cm abdominal laparotomy in anaesthetised rats. These findings suggest that constitutive NO synthase effectively counteracts the damaging actions on microvascular integrity of mediators, including thromboxanes, PAF, leukotrienes and vasopressin, released during surgical intervention.

The mechanism of inhibition of porcine leukocyte 12-lipoxygenase by 4-(2-oxapentadeca-4-yne)phenylpropanoic acid (OPP) was investigated. This compound is selective for the leukocyte form of the 12-lipoxygenase and inhibits the purified recombinant enzyme with an IC(50) value of approximately 2 microM. OPP induced a concentration-dependent lag phase in the oxygenation of arachidonic acid and decreased the maximal rate of reaction. Addition of the fatty acid hydroperoxide 13(S)-hydroperoxyoctadecadienoic acid (13-HPODE) to the reaction greatly reduced the OPP-induced lag. Lineweaver-Burk analysis of the effect of OPP on 12-lipoxygenase kinetics with arachidonic acid indicated that it was a mixed-type inhibitor. OPP was not metabolized by 12-lipoxygenase as evidenced by its quantitative recovery from incubations with stoichiometric amounts of enzyme and 13-HPODE or arachidonic acid. OPP inhibited the pseudoperoxidase activity of the enzyme with 13-HPODE and the reducing agent, BWA137C. Lineweaver-Burk analysis of the effect of OPP on pseudoperoxidase kinetics suggested that OPP was competitive with 13-HPODE. Single-turnover experiments indicated that OPP inhibited the reduction of 13-HPODE by a stoichiometric amount of ferrous 12-lipoxygenase. Addition of 13-HPODE shortened the OPP-induced lag phase but did not affect the maximal rate of enzyme activity. In addition, OPP had no effect on total product formation in either the presence or the absence of 5 microM 13-HPODE when the reaction was allowed to go to completion. All of these observations are consistent with a model for inhibition of 12-lipoxygenase activity in which OPP slows the oxidation of the inactive ferrous enzyme to the active ferric enzyme and competes with arachidonic acid for the ferric enzyme.