Inter-relationships between inflammatory mediators released from colonic mucosa in ulcerative colitis and their effects on colonic secretion.

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Abstract
Metabolites of arachidonic acid have been implicated in the pathophysiology of ulcerative colitis-they can stimulate intestinal secretion, increase mucosal blood flow, and influence smooth muscle activity. The influence on the mucosal transport function of culture medium in which colonic mucosal biopsy specimens had been incubated was investigated using rat stripped distal colonic mucosa in vitro as the assay system. Colonic tissue from patients with colitis and from control subjects was cultured. Medium from inflamed tissue contained more prostaglandin E2 (PGE2) and leukotriene D4 (LTD4) and evoked a greater electrical (secretory) response in rat colonic mucosa than control tissue medium. In inflamed tissue, cyclo-oxygenase inhibition (indomethacin) attenuated PGE2 but increased LTD4 production; conversely lipoxygenase inhibition (ICI 207968) inhibited LTD4 production but enhanced PGE2 output. Each inhibitor alone enhanced the electrical response in the rat colon. Inhibition of both enzymes (indomethacin plus ICI 207968) caused a fall in both PGE2 (82%) and LTD4 (89%) production and in the electrical response (57%). Inflamed tissue treated with a phospholipase A2 inhibitor (mepacrine) produced less PGE2, LTD4, and electrical responses when compared with inflamed tissue, either untreated (91%, 92%, and 79% respectively) or treated with cyclo-oxygenase and lipoxygenase inhibition. Incubation with bradykinin stimulated eicosanoid release and electrical response, while a bradykinin antagonist caused a modest inhibition. Analysis of these observations suggests that a combination of arachidonic acid derivatives accounts for about half the secretory response. Other products of phospholipase A2 activity are probably responsible for much of the remainder, leaving up to 20% the result of types of mediator not determined in this study.