The mast cells and an experimental gastric ulcer. Histochemical, ultrastructural and quantitative study in the rat.

The role of mucosal mast cells (MMC) in chronic non-allergic reactions of the gastric mucosa is unknown. The present study aimed to investigate the reaction of gastric MMC during healing of the acetic acid-induced gastric ulcer in the rat. Mast cells were stained with toluidine blue and alcian blue+safranin and their density and distribution were assessed. Morphometry of MMC and documentation of their contact with eosinophils were based on electron microscopy. In the normal non-injured rat oxyntic mucosa MMC are grouped in two populations: MMC1 concentrated near the glandular necks, and MMC2 in the basal lamina propria. There was a significant decrease in the number of MMC2 near the ulcer, whereas MMC1 lost their concentration in the neck zone. Also the MMC/connective tissue mast cells ratio was increased in the gastric wall adjacent to the ulcer. Eosinophils were commonly in close contact with MMC. Eosinophil cytoplasm adjacent to MMC was devoid of organelles, which were accumulated in the central cytoplasm. The significant redistribution of mast cell population as well as numerous close contacts between mucosal mast cells and eosinophils, taking place in the neighborhood of the chronic gastric ulcer, seem to be not only of morphological but also of functional significance.