[pH gradient support and antacid action of gastroesophageal coating agents. In vitro pharmacologic study using a model of "the artificial stomach"].

The effects of gastroesophageal mucosal coating agents could be related to a) the decrease of aggressive contents of gastric juice and/or b) the presence of a pH gradient between intraluminal (IL) contents and mucosa. Antacid capacities of Gaviscon and Topaal, containing sodium alginate or alginic acid, respectively, were measured using the "artificial stomach" model. This model, reproducing two major gastric dynamic functions, secretion and gastric emptying, allows to evaluate the pH variations in the IL contents and at its surface, by a double pH metric recording. Experiments were performed when drugs to be tested were added either to 100 ml of human gastric juice (100 mmol/l or 88 mmol/l with biliary reflux) or to 100 ml of 0.1 N HCl, without and with 1 percent meat extract. Simulated secretion was represented by a 3 ml/min flux of either 0.1 N HCl or gastric juice and "gastric emptying" fluxes varied from 1.5, 3.0 to 4.5 ml/min. When 0.1 N HCl solution was used, the pH levels at the surface of IL contents were close to pH 3.0 when intragastric pH reached pH 1.0 independently of "gastric" emptying flux variations. In the presence of proteins or biliary reflux material, these pH levels were higher, close to pH 4.5 and persisted for a longer time. Antacid activity was calculated as the resistance to acidification of the IL contents, as the amount of H+ ions consumed after addition of antacid to recover initial pH, i.e. 37 and 22 mmol in human gastric juice, between 37 and 17.5 mmol in 0.1 N HCl for Gaviscon and Topaal, according to emptying fluxes.(ABSTRACT TRUNCATED AT 250 WORDS)