Effect of the acid secretory state on intramural pH of rabbit gastric mucosa.

Intramural pH of the gastric mucosa was measured using a microelectrode technique in rabbit gastric pouches under different secretory conditions and luminal acidity. Exposure of spontaneously secreting or metiamide-treated fundic pouches to a relatively high concentration of luminal acid. HCl 120 mM, for 60 min, led to a marked net loss of luminal H+ which was associated with a significant decrease in the intramural pH (7.28 +/- 0.09 to 6.88 +/- 0.10 and 7.23 +/- 0.07 to 6.99 +/- 0.09, respectively). A linear relationship was observed between the rates of net disappearance of luminal acid and the intramural pH. All 10 spontaneously secreting and five metiamide-treated pouches had superficial mucosal erosions. In contrast, when fundic pouches were exposed to luminal acid in histamine-treated animals, the net loss of luminal H+ was negligible and the intramural pH remained at its base-line level (7.25 +/- 0.07). Histamine stimulation without acid in the lumen caused a small but insignificant increase in the intramural pH (7.27 +/- 0.03 to 7.39 +/- 0.05). Only three of the eight histamine-treated fundic pouches had lesions. In the antral pouches the intramural pH changes in response to exposure to luminal acid were smaller and histamine treatment did not influence the intramural pH. None of the antral pouches had lesions. The results suggest that acidification of the tissue by the diffusion of luminal acid may be an important factor in the pathogenesis of acute gastric ulceration. The acid secretory state of the gastric mucosa can significantly influence the acid-base balance in the mucosa and thus modify its response to acid diffusing from the lumen. Histamine stimulation protected the gastric mucosa by improving its buffering capacity and/or otherwise decreasing the diffusion of H+ from the lumen into the mucosa.