Inhibitory effect of famotidine on cat gastric secretion

The inhibitory effect of the novel H2 receptor antagonist famotidine was studied in conscious gastric fistula cats against dimaprit-induced hypersecretion, in comparison with ranitidine. On the secretory plateau induced by dimaprit (2 mumol kg-1 h-1) famotidine (0.05-0.2 mumol kg-1 i.v.) exerted a dose-dependent inhibitory effect, being approximately 4.5 times as potent as ranitidine (ID50 values were 0.067 +/- 0.015 and 0.30 +/- 0.025 mumol kg-1 for famotidine and ranitidine, respectively). No significant differences were found between the two drugs, as for the time-course of the inhibitory effect. Famotidine (0.01-0.32 mumol kg-1 h-1) caused a parallel displacement of the dose-response curve to dimaprit to the right, without reducing the maximum response to the stimulant, thus behaving as a competitive antagonist, like ranitidine. pA2 values for famotidine and ranitidine were 7.95 and 6.92, respectively. In the same range of doses famotidine dose-dependently reduced also the secretory response to histamine. From these data it was concluded that famotidine is a potent histamine H2 receptor antagonist in the cat gastric mucosa; moreover, conversely from "in vitro" data, the antagonism was surmountable even at the highest doses tested. In vivo experiment, therefore, did not reveal any particular feature of this compound, apart from the undoubtedly high potency, in comparison with other members of the family.