Effect of topical bile acids on gastric surface epithelial cells

Attempts to assess the integrity of the gastric surface epithelial cell layer have been hampered by the lack of a quantitative index of surface cell injury. Two approaches: scanning electron microscopy and measurement of DNA efflux (DNAE) were used to assess surface cell injury produced by topical bile acids. Taurocholic acid (TC) at 0, 2.5, 5, and 10 mM concentrations in both neutral (NTS, pH = 7.0) and acid test solution (ATS, pH = 1.2) was applied to chambered vascularized wedges of proximal canine gastric mucosa for sequential 30-minute study periods. In part I surface cell morphology was assessed by scanning electron microscopy in 28 mucosae exposed to NTS, NTS + TC, ATS, or ATS + TC, and the effect of the mucolytic agent N-acetyl-L-cysteine (acetylcysteine) at pH 7.0 was studied in 10 additional mucosae. In part II DNAE, net cation fluxes, and mean potential difference (PD) per 30-minute period were measured. In 16 animals 10% acetylcysteine was applied topically after period III to dissolve gastric mucus and allow recovery of exfoliated cells. Nineteen additional mucosae were treated with acetylcysteine between each study period.

By scanning electron microscopy, mucosae exposed to NTS, NTS + TC, or ATS maintained an intact layer of surface epithelial cells. ATS + TC induced dose-dependent exfoliation of sheets of surface cells. Compared with NTS, neither NTS + TC nor ATS altered DNAE; DNAE increased only in mucosae exposed to ATS + TC. Compared with ATS, ATS + TC increased cation fluxes and decreased PD (p less than 0.05). DNAE correlated with delta H+, delta Na+, delta K+, and PD (r = 0.95, 0.93, 0.86, and 0.89) (all p less than 0.05). Pretreatment with acetylcysteine increased Na+ flux in mucosae exposed to NTS and ATS but otherwise did not change delta H+, delta K+, DNAE, or PD. In mucosae exposed to ATS + TC, DNAE paralleled morphologic changes in the surface epithelial layer and physiologic alterations in cation fluxes and PD. Both scanning electron microscopy and measurement of DNAE appear to be useful tools in assessing surface epithelial cell injury.