The antisecretory activities of 4-(dimethylamino)- N-[2-[3-[3-(1-piperidinyl)methyl]phenoxy]propyl]amino]- 1,2,5-thiadiazol-4-yl]amino]ethyl]-butanamide, S-oxide (AY-29,315) and ranitidine were determined in the rat, dog and monkey. In conscious, chronically cannulated rats, AY-29,315 was 10 and 208 times more potent than ranitidine as an inhibitor of spontaneous gastric acid secretion by the p.o. and i.v. routes, respectively. Tolerance did not develop in the conscious rat with either compound when administered for 8 consecutive days at doses equivalent to 4 times their antisecretory ED50. In lumen-perfused, anesthetized rats, AY-29,315 i.v. was 44 times more potent than ranitidine as an inhibitor of dimaprit-induced acid secretion. In the gastric fistula dog, AY-29,315 was 7.5 times more potent than ranitidine as an inhibitor of dimaprit-induced secretion by the i.v. route but 3 times less potent by the oral route. In the monkey, against dimaprit, AY-29,315 was 3 and 12 times more potent than ranitidine by the oral and i.v. routes, respectively. p.o./i.v. ratios indicate that, relative to ranitidine, the bioavailability of AY-29,315 by the oral route was low, particularly in the dog. In the dog, at 4 times the oral ED50 dose, the antisecretory effect of ranitidine lasted 190 +/- 3 min, while that of AY-29,315 lasted more than 9 h. AY-29,315 was 8 times more potent than ranitidine as an inhibitor of acetylsalicylic acid-induced ulcers in the rat.(ABSTRACT TRUNCATED AT 250 WORDS)