The effect of cimetidine on the basal gastric acid secretion of the rat has been investigated in an anaesthetized lumen-perfused preparation. 2. Six rats previously given large doses of cimetidine orally showed no significant difference in basal gastric acid secretion when compared with six control rats. 3. Intravenous administration of 1 mg and 8 mg of cimetidine failed to inhibit significantly basal gastric acid secretion. 4. Although rats with a basal gastric acid secretion above 2.5 micro Eq/10 min. showed a consistent small reduction in basal gastric acid secretion after intravenous cimetidine, this was not seen in rats with a basal gastric acid secretion below 2.5 micro Eq/10 min. 5. THese results contrast sharply with the pronounced inhibition of basal gastric acid secretion by cimetidine in man and the possible reasons for this are discussed. 6. The results are also contrasted with previous work on gastric fistula rats which showed higher basal gastric acid secretion and significant inhibition by cimetidine.
