Eicosanoid regulation of acute intestinal vascular permeability induced by intravenous peptidoglycan-polysaccharide polymers

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Abstract
A model of rapidly developing, self-limited acute vascular permeability changes localized to the gutassociated lymphoid tissue (GALT) of the rat was used to study the role of prostaglandins (PGs), thromboxanes (Txs), and leukotrienes (LTs) in thein vivo regulation of early intestinal inflammatory events. Sprague Dawley rats were pretreated with metabolites, enzyme inhibiors, or receptor antagonists of the arachidonic acid pathway before intravenous injection of sonicated peptidoglycan-polysaccharide polymers derived from group A streptococci (PG-APS, 5 μg rhamnose/g body weight). Rats were killed five minutes after PG-APS injection and were evaluated grossly for petechiae of the intestinal parencyma and lymphoid aggregates. Indomethacin or dexamethasone increased intestinal injury by PG-APS by inducing mid-small bowel and cecal parenchymal hemorrhage. Indomethacin significantly diminished colonic lymphoid aggregate hemorrhage. PGE1, PGE2, and prostacyclin dramatically inhibited GALT hemorrhage; prostacyclin was the most potent with an effective dose of 0.1 μg/kg. Dazmegrel, a specific Tx synthetase antagonist, significantly inhibited PG-APS-induced vascular permeability. Dazmegrel continued to diminish colonic lympoid aggregated hemorrhage during concurrent treatment with indomethacin, which removed potential endogenous prostaglandin protection. Diethylcarbamazine, a lipoxygenase inhibitor, and FPL-55712, a LT receptor antagonist, inhibited the PG-APS-induced lesions, with FPL-55712 being more potent. LT blockade had a predominant effect on the intestinal parenchymal hemorrhage. We postulate that the normal suppression of inflammation induced by phlogistic bacterialcell wall polymers is PG mediated, and that pathological responses are Tx and LT dependent.

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