Cholinergic-mediated gastric mast cell degranulation with subsequent histamine H1-and H2-receptor activation in stress ulceration in rats.

The effects of atropine, mepyramine, metiamide or NaHCO3 on gastric ulceration, gastric secretion and gastric mast cell degranulation were studied in stressed pylorus-occluded rats. The influence of dexamethasone pretreatment on stress ulcers in animals without pylorus occlusion (intact rats) was also examined. Stress produced a high glandular lesion incidence and ulcer index, and markedly lowered gastric secretion and glandular wall mast cell counts. Injected 0.5 h before stress, atropine, mepyramine or metiamide strongly antagonised ulceration. Atropine or metiamide, but not mepyramine, reduced gastric secretion. Only atropine prevented stress-induced mast cell changes. NaHCO3, given intragastrically before stress, did not prevent ulceration or mast cell degranulation despite complete neutralisation of gastric acid. Dexamethasone-induced gastric mucosal mast cell depletion could reduce stress ulceration. The findings show that stress degranulates stomach mast cells via a cholinergic pathway; released histamine from this source is largely responsbile for gastric ulceration through H1- and H2-receptor effects. Histamine H2-receptor-mediated gastric acid may play only a small contributory role in stress ulcers in rats. The antiulcer mechanisms of histamine H1- and H2-receptor blockade are discussed.