Picomole doses of platelet-activating factor predispose the gastric mucosa to damage by topical irritants.

The ability of the endogenous pro-inflammatory phospholipid, platelet-activating factor (Paf), to increase the susceptibility of the rat gastric mucosa to damage induced by a topical irritant was studied in an ex vivo gastric chamber model. Intravenous infusion of Paf (1-100 ng/kg/min) for 5 minutes dose-dependently increased the haemorrhagic damage induced by topically applied 20% ethanol. The pro-ulcerogenic actions of Paf were not solely due to its hypotensive actions, since a significant augmentation of damage was observed with doses of Paf (1 ng/kg/min) which did not affect systemic arterial blood pressure. These pro-ulcerogenic actions were not shared by the structurally similar precursor/breakdown product, lyso-Paf (100 ng/kg/min). Paf (100 ng/kg/min) also significantly increased the gastric damage induced by topically applied 2 mM sodium taurocholate. Infusion of Paf for 5 minutes without topical irritation only caused significant gastric damage at the highest dose tested (100 ng/kg/min). Histologically, this damage was characterized by extensive vasocongestion, deep mucosal necrosis, swelling of the gastric glands and accumulations of neutrophils in the mucosal and submucosal venules. Paf is thus a potent pro-ulcerogenic agent in the gastric mucosa. The endogenous release of Paf during septic shock or inflammatory diseases of the gastrointestinal tract could contribute to the mucosal injury associated with these disorders.