The role of xanthine oxidase in platelet activating factor induced intestinal injury in the rat

Background-Xanthine oxidase (XO) is an important source of reactive oxygen species in the small intestine. Aims-To examine the interaction of platelet activating factor (PAF), XO, an d neutrophils in mediating intestinal injury in rats. Methods-Two doses of PAF were used to induce either reversible hypotension, or irreversible shock with intestinal necrosis. The activities of XO, and its precursor xanthine dehydrogenase (XD), in both the whole intestinal tis sue and epithelial cells, were measured. XO was localised by histochemical staining. Results-PAF dose dependently induced an increase in XO activity, predominan tly in the ileal epithelium, without altering the total activity of XD+XO. Most of the XD to XO conversion was via proteolysis. PAF induced XO activat ion and intestinal injury were prevented by prior neutrophil depletion. PAF induced XO activation is probably not due to reperfusion, as XO activation preceded the recovery of mesenteric flow. Allopurinol pretreatment substan tially inhibited intestinal neutrophil sequestration induced by high dose ( but not low dose) PAF. Conclusions-PAF rapidly activates intestinal XO through proteolytic XD-XO c onversion, predominantly in the ileal epithelium. This effect is mediated b y neutrophils. XO activation promotes PAF induced polymorphonuclear leucocy te sequestration in the intestine.