H2-receptor antagonists protect against aspirin-induced gastric lesions in the rat

Gastric mucosal lesions were produced in rats by dosing orally with aspirin, 300 mg/kg. Predosing orally with either ranitidine or cimetidine inhibited this lesion formation; the respective ED50 values were 0.8 and 3.9 mg/kg p.o. Oral ranitidine also inhibited lesion formation in the presence of exogenous 160 mM HCl, with an ED50 value of 23.2 mg/kg p.o. Subcutaneous injection of ranitidine inhibited the formation of aspirin-induced lesions both in the presence and in the absence of excess HCl. The ED50 values were respectively 3.4 and 0.9 mg/kg s.c. Mepyramine maleate (5 mg/kg p.o.) alone had no effect on gastric lesion formation, and did not influence the level of inhibition produced by ranitidine either in the absence of presence of exogenous acid.