Comparison of the Step-Dose and Single-Dose Acid Response to Histamine and Pentagastrin in Chronic Gastric Fistula Rats

Abstract

Time-response and dose-reponse curves for acid output to continuous infusion of histamine (HIST) and pentagastrin (PG) wre determined by 2 techniques in conscious rats provided with chronic gastric fistula. With the step-dose technique the dose of the stimulant was increased each h; with the single-dose technique only 1 dose of the stimulant was administered on each test day. Observed maximum acid output (OMAO) was obtained either by infusion of PG at a rate of 6 .mu.g/kg per h using both techniques or HIST at a rate of 1 mg/kg per h with the single-dose and 2 mg/kg per h with the step-dose technique. These OMAO were in the order: single PG > single HIST > step HIST > step PG in ratios 100:99:83:82. Dose-response curves were analyzed by application of the Michaelis-Menten equation. For each stimulant there was no difference betweeen calculated maximum acid output (CMAO) whatever the technique used, but PG gave lower CMAO than HIST (P < 0.05). For both stimulants the calculated doses for half the calculated maximal response (CD 50) are significantly higher with the step-dose than with the single-dose technique. These results are compared with those previously described in the literature for cats, dogs and man.