The effects of stimulants and inhibitors of histamine receptors on acid secretion from guinea pig gastric fundus

Two selective H₂ receptor stimulants (5-methyl-N-methylhistamine and dimaprit) so far never tested in isolated gastric preparations, were found to be strong stimulants of acid secretion from the guinea pig isolated gastric fundus. Although some differences were observed in the cumulative dose-response curves for these two agonists, the peak responses obtained were not significantly different from the maximum response to histamine. Cimetidine produced parallel displacement of the dose-response curves to the right with the maximum response unchanged, suggesting competitive antagonism on H₂ receptors. The dose-response curve for histamine was not affected by the simultaneous administration of an H₁ receptor agonist, 2(2-aminoethyl)thiazole, or of an H₁ receptor antagonist, pyrilamine. This indicates that the action of histamine on the isolated guinea pig gastric fundus is associated exclusively with H₂ receptor stimulation.