Background and objectives: Mesenteric microvascular thrombosis may be an early pathogenic event in Crohn's disease (CD), and intravascular platelet aggregates have been identified in mucosal biopsies in ulcerative colitis (UC). Activated platelets are involved in thrombogenesis and exhibit inflammatory properties. In active inflammatory bowel disease (IBD) increased numbers of platelet aggregates are detectable in the peripheral circulation. The aim of this study was to test the hypothesis that in IBD, platelet aggregation is triggered in the mesenteric vasculature.
Patients and methods: Platelet numbers, platelet aggregate 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 disease.
Results: In UC and CD, but not in controls, fewer neutrophils were found in blood draining the intestine compared with that supplying 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 platelet aggregates were identified in venous samples (platelet aggregate 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 < 0.05). The mesenteric arteriovenous gradient for neutrophils in IBD reflects their migration into the extravascular tissue and lumen of the inflamed intestine. Increased circulating platelet aggregates in the mesenteric venous circulation support the hypothesis that platelet activity is stimulated in the mesenteric microcirculation in CD.