Intragastric titration of acid in the perfused rat stomach preparation following parenteral and intraluminal stimulation.

The anaesthetised rat stomach preparation was adapted to assay intraluminally administered stimulants and inhibitors of acid secretion by continuously recirculating the perfusate (15 ml of 5% glucose) and measuring acid by the pH-stat technique. The responses obtained were linear. Continuous artificial neutralisation of the stomach to pH 5.5 as well as variation of the pH between 6.5 and 4.0 did not significantly alter the sensitivity of the preparation to intravenously administered human gastrin-heptadecapeptide I (HG I). Basal acid secretion however significantly declined following stepwise lowering of the intragastric pH between 6.5 and 4.0. The threshold values for responses to i.v. HG I were below 16 ng. 6 doses could be given per rat without tachyphylaxis. Acetylcholine, 1.3, 2.5, 5.2 and 10.4 micron g/ml in the perfusate, induced a dose-dependent linear (r=0.902) acid secretion. Metiamide 1.66 mg/ml in the perfusate, produced a parallel shift to the right of the HG I dose--response curve producing an agonist dose ratio of 3.66. The data suggest that intragastrically applied stimulants and inhibitors of acid secretion can be studied precisely in this relatively simple preparation.