This study was designed to quantitatively discriminate the specific xanthine oxidase (XO) inhibitory from the relatively nonspecific antioxidant activities of allopurinol, both in vitro and in vivo in the rat. XO activity, determined by the spectrophotometric assay for urate generation over time, was completely inhibited in vitro by allopurinol at concentrations > or = 200 microM. Allopurinol's antioxidant activity was determined in vitro using a linolenic acid peroxidation (LAP) assay. Although the known antioxidant butylated hydroxytoluene effectively inhibited LAP (80% inhibition of malondialdehyde generation at 10(1) microM), allopurinol (10(1)-10(3) microM) did not inhibit this LAP (p < .01). Rat serum obtained after oral administration of allopurinol (100 mg/kg x 2 doses) did not suppress LAP in vitro more than did control rat serum. Following oral administration of allopurinol (2-50 mg/kg x 2 doses), dose-dependent inhibition of XO activity was observed in the homogenates of the liver (to 5% of control level; p < .001) and the intestine (to 12% of control level; p < .001). We conclude that while 2-50 mg/kg of oral allopurinol effectively suppresses XO activity in the rat liver and intestine, antioxidant activity is not seen even in doses up to 100 mg/kg. The selective enzymatic inhibitory effect of allopurinol at these doses therefore should provide a useful tool to allow the discrimination of the effects of xanthine oxidase in particular from the effects of reactive oxygen metabolites in general.

Most studies of neutrophil-endothelial interactions in vivo necessarily require the use of general anesthetic agents which are well known to be immunosuppressive. By using whole-mount preparations of the rat mesoappendix, we were able to study tumor necrosis factor alpha (TNF-alpha) induced neutrophil adhesion to the mesenteric venular endothelium in vivo without necessarily using general anesthesia. TNF-alpha significantly increased venular-neutrophil accumulation in a dose-dependent manner, accumulation was markedly increased at 1, 2, and 4 h, but returned to baseline after 24 h. After these preliminary dose-response and time-course studies, we evaluated the influence of standard clinically effective doses of several commonly used anesthetic agents (thiopental, pentobarbital, ketamine, alpha-chloralose, methoxyflurane, and halothane) on the extent of neutrophil-venular accumulation induced 2 h after intraperitoneal injection of 0.4 mg/kg TNF-alpha, compared to unanesthetized rats. All general anesthetics tested, with the exception of methoxyflurane, significantly suppressed this response. In most cases this suppression was striking (from 60 to 85%) such that a statistically significant proinflammatory response was obscured. Although methoxyflurane also tended to suppress this response to TNF-alpha, it was the only agent that allowed the response to be clearly seen. Because anesthesia markedly suppresses cytokine-induced neutrophil-venular adhesion, this model should provide an important complementary technique to the classical in vivo microcirculatory approaches which do necessarily require general anesthesia.

We investigated the role of reactive oxygen metabolites (ROMs) as potential mediators of tumor necrosis factor-alpha (TNF-alpha)-stimulated neutrophil adhesion to rat mesenteric venules in vivo, using intravital microscopy and fixed whole mount preparations of mesentery. Intraperitoneal injection of TNF-alpha significantly increased leukocyte rolling, adhesion, and emigration in a dose- and time-dependent manner. Leukocyte adhesion and emigration, but not rolling, were significantly attenuated by prior intravenous administration of monoclonal anti-intercellular adhesion molecule-1 (ICAM-1). Rolling leukocyte flux was significantly attenuated by intravenous preadministration of superoxide dismutase (SOD), catalase, or both. Only catalase or SOD plus catalase significantly inhibited leukocyte adhesion. Catalase alone inhibited emigration. Moreover, postadhesive treatment with catalase but not SOD, 4 h after TNF-alpha administration reduced the flux of rolling (but not adherent) leukocytes that had previously increased in response to TNF-alpha. Intragastric allopurinol (50 mg/kg at 3 and 18 h before TNF-alpha administration) or 3 wk of a tungsten-enriched diet substantially inhibited xanthine oxidase activity but had no significant effects on the above parameters of neutrophil dynamics. In parallel experiments using fixed whole mount preparations of the mesoappendix stained specifically for neutrophil esterase, neutrophil adhesion 2 h after TNF-alpha administration was also inhibited by continuous intravenous administration of catalase but not by SOD, intragastric allopurinol, or tungsten diet. These findings suggest that ROMs, apparently not from xanthine oxidase, are important mediators of TNF-alpha-induced upregulation of neutrophil adhesion in rat mesenteric venules.

Toxic metabolites of oxygen are generated normally by aerobic metabolism in cells and this generation can significantly increase in certain pathologic conditions. When endogenous antioxidant defense capabilities are exceeded by this oxidant flux, tissue injury occurs. This process can be intercepted pharmacologically at different levels with agents that scavenge reactive oxygen metabolites, block their generation, or enhance endogenous antioxidant capabilities. In many situations, such as the treatment of post-ischaemic reperfusion injury, efficacy of antioxidant is related primarily to the proportionate magnitude of the total injury sustained that is due to an antioxidant mechanism. This approach has shown great promise in animal models of clinical problems and has been tested successfully in early, controlled clinical trials.