PLATELET-AGGREGATION AND NEUTROPHIL SEQUESTRATION IN THE MESENTERIC CIRCULATION IN INFLAMMATORY BOWEL-DISEASE

Background and objectives: Mesenteric microvascular thrombosis may be an early pathogenic event in Crohn's disease (CD), and intravascular p latelet aggregates have been identified in mucosal biopsies in ulcerat ive colitis (UC). Activated platelets are involved in thrombogenesis a nd exhibit inflammatory properties. In active inflammatory bowel disea se (IBD) increased numbers of platelet aggregates are detectable in th e peripheral circulation. The aim of this study was to test the hypoth esis that in IBD, platelet aggregation is triggered in the mesenteric vasculature. Patients and methods: Platelet numbers, platelet aggregat e ratios and differential leucocyte counts were compared in mesenteric arterial and venous blood obtained from paired vessels at the time of intestinal resection from 13 patients with inflammatory bowel disease and, as controls, 6 patients with colonic carcinoma or diverticular d isease. Results: In UC and CD, but not in controls, fewer neutrophils were found in blood draining the intestine compared with that supplyin g it (arteriovenous gradient median 1.0 x 10(9)/l (interquartile range 0.2-1.3) for UC, P < 0.05; 0.8 (0.2-1.5) for CD, P < 0.02; 0.4 (-0.3- 1.1) for controls, P = NS). In CD, increased numbers of circulating pl atelet aggregates were identified in venous samples (platelet aggregat e ratio 0.83 (0.71-0.93)) than in paired arterial samples (0.99 (0.95- 1.01), P < 0.02) and control venous samples (0.99 (0.93-0.97), P < 0.0 5). The mesenteric arteriovenous gradient for neutrophils in IBD refle cts their migration into the extravascular tissue and lumen of the inf lamed intestine. Increased circulating platelet aggregates in the mese nteric venous circulation support the hypothesis that platelet activit y is stimulated in the mesenteric microcirculation in CD.