Regulation of platelet-activating factor production in gastric epithelial cells

The authors have previously reported that platelet-activating factor (PAF), a phospholipid mediator with potent proinflammatory activities, is produced in the gastric mucosa and stimulates gastric acid secretion in humans and animals. In the present study they used the human gastric tumour cells HGT1 (clone 6) to examine whether PAF production is regulated by neuromediators. PAF was extracted by ethanol and assayed by the washed platelet aggregation test. HGT1 cells produced PAF spontaneously (110 +/- 20 pg 10(6) cells). The addition of vasoactive intestinal peptide (VIP; 10(-9) to 10(-7) mol L(-1)) or of histamine (10(-5) to 10(-3) mol L(-1)) increased PAF production by three- to fivefold, while the addition of carbachol (10(-7) to 10(-4) mol L(-1)) increased PAF production up to sevenfold. PAF production was also increased up to 10- to 13-fold, in a dose- and time-dependent manner, by the addition of calcium and two- to threefold by the addition of phorbol myristate acetate (PMA; 10(-7) to 10(-5) mol L(-1)). However, the addition of dibutyryl cyclic AMP (dBcAMP; 10(-6) to 10(-4) mol L(-1) was without any effect. This is the first report showing PAF production by gastric epithelial cells in response to histamine, VIP and carbachol. Furthermore, the findings are consistent with a central role of calcium in this production. The results of this study, together with those of previous studies from the authors' laboratory, support the hypothesis that PAF is a physiological mediator of gastric acid secretion.