Stomach ulcer and lysosomal cathepsin.

Gastric ulcers were induced in rats by i.m. injections of vitamin A, and i.p. injection of histamine, or injections of both vitamin A and histamine. The incidence of ulcer formation was highest in the vitamin A-histamine group. However, ulcer formation also occurred after the administration of vitamin A alone as a lysosomal labilizer. Furthermore, the vitamin A-histamine group showed a remarkably elevated cathepsin activity in the tissue of gastric wall. In the experiments of ulcer formation by vitamin A injections, the specific activity and the enzyme release of cathepsin were elevated already in the early stage after vitamin A administration. Consequently, cathepsin activity in stomach juice was remarkably elevated in the stage of the ulcer formation. In the clinic, the cathepsin activity in the mucous membrane of human gastric wall was remarkably high in the antrum and the angulus of the stomach, in which ulcer formation tends to occur most frequently. In view of these results, cathepsin in the stomach seems to play an important role in the formation of gastric ulcers.