Increased parietal cell sensitivity after chronic treatment with ranitidine in the conscious cat.

The sensitivity of histamine H2 receptors of the gastric mucosa after one month treatment with ranitidine, administered daily (5 mg/kg i.m.), was checked in 5 conscious cats provided with gastric fistula. Basal acid secretion as well as the acid response to the H2 agonist dimaprit (60 micrograms/kg/hr) were studied before and at different periods after cessation of ranitidine treatment (1, 3, 7 and 14 days). Control experiments were carried out in 5 gastric fistula cats which received daily physiological saline for one month. Basal acid secretion in treated animals increased significantly (p less than 0.05) from 0.04 +/- 0.002 to 0.24 +/- 0.05 mEq H+/10 min. Also the response to dimaprit increased significantly (p less than 0.05) from 0.49 +/- 0.08 to 0.86 +/- 0.12 mEq H+/10 min. Seven days after cessation of treatment, both basal and stimulated secretion returned to pretreatment levels. In control cats no significant difference was noticed in basal and stimulated secretion at the beginning and at the end of the study.