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We have developed an in vitro model of adaptive cytoprotection induced by deoxycholate (DC) in human gastric cells and have shown that pretreatment with a low concentration of DC (mild irritant, 50 μM) significantly attenuates injury induced by a damaging concentration of DC (250 μM). This study was undertaken to assess the effect of the mild irritant on changes in intracellular Ca2+ and to determine if these perturbations account for its protective action. Protection conferred by the mild irritant was lost when any of its effects on intracellular Ca2+ were prevented: internal Ca2+ store release via phospholipase C and inositol 1,4,5-trisphosphate sustained Ca2+ influx through store-operated Ca2+ channels or eventual Ca2+ efflux. We also investigated the relationship between Ca2+accumulation and cellular injury induced by damaging concentrations of DC. In cells exposed to high concentrations of DC, sustained Ca2+ accumulation as a result of extracellular Ca2+ influx, but not transient changes in intracellular Ca2+ content, appeared to precede and induce cellular injury. We propose that the mild irritant disrupts normal Ca2+ homeostasis and that this perturbation elicits a cellular response (involving active Ca2+ efflux) that subsequently provides a protective action by limiting the magnitude of intracellular Ca2+ accumulation.

Gallbladder tissue from patients with acute acalculous cholecystitis contains increased amounts of prostanoids when compared to normal gallbladder tissue. Platelet-activating factor (PAF) is a potent stimulus of eicosanoid formation. It has been implicated as a mediator of acute inflammatory processes and systemic responses to shock. In this study the role of PAF in acute acalculous cholecystitis was evaluated. Anesthetized cats underwent gallbladder perfusion with a physiologic buffer solution containing [14C]polyethylene glycol as a nonabsorbable tracer to quantitate mucosal water absorption. Platelet-activating factor was infused into the hepatic artery for 2 hours. Control experiments were performed when vehicle alone was infused. Experiments also were performed when indomethacin was administered intravenously and when indomethacin and PAF were administered. Gallbladder mucosal absorption/secretion and perfusate and tissue prostaglandin E (PGE) and 6 keto prostaglandin F1 alpha (6-keto PGF1 alpha) levels were evaluated. Gallbladder inflammation was evaluated by beta-glucuronidase and myeloperoxidase tissue concentrations and by a histologic scoring system. Platelet-activating factor eliminated gallbladder absorption and produced net fluid secretion associated with dose-related increases in perfusate PGE concentrations and gallbladder tissue PGE and 6 keto PGF1 alpha levels when compared to control values. Platelet-activating factor produced significant inflammation in the gallbladder with increases in the histologic score of inflammation and tissue lysosomal enzyme activities. Indomethacin significantly decreased the fluid secretion, prostanoid levels, and inflammation produced by PAF. The results suggest that PAF may induce acute gallbladder inflammation associated with systemic stress through a prostanoid-mediated mechanism.

Indomethacin and other nonsteroidal anti-inflammatory drugs are commonly used to indirectly deduce the possible role of PGs in a process being studied. The objective of this study was to determine if indomethacin, at concentrations comparable to plasma and tissue levels obtained in humans taking therapeutic doses, predisposes human gastric cells to injury through inhibition of PGs or acts through an alternate mechanism. The role of intracellular Ca2+ in this damaging process was also assessed. Indomethacin pretreatment, although by itself nondamaging, was associated with elevated intracellular Ca2+ concentrations and an increased cellular permeability, an effect that was dependent on extracellular Ca2+. Furthermore, indomethacin pretreatment significantly predisposed AGS cells to injury induced by two dissimilar agents (deoxycholate and A-23187), both of which are associated with intracellular Ca2+ accumulation. The addition of exogenous PGs did not reverse the predisposition to injury induced by indomethacin. The observed effects of indomethacin were dependent on concentration and not on ability to inhibit PG synthesis. Similar effects were not observed with equipotent concentrations of ibuprofen or aspirin. Finally, the exacerbation of deoxycholate-induced injury induced by indomethacin was not observed when extracellular Ca2+ was removed. Indomethacin, by disturbing intracellular Ca2+homeostasis, predisposes human gastric cells to injury through mechanisms independent of PG synthesis. The current study suggests that data resulting from studies employing only indomethacin as a PG synthesis inhibitor should be interpreted with caution.

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