Acute effects of ranitidine, famotidine and omeprazole on plasma gastrin in the rat.

In the rat, treatment with gastric inhibitory drugs may result in hypergastrinemia, an effect thought to be in response to increased gastric pH caused by inhibition of acid secretion. This study compared 24-hr profiles of plasma gastrin levels associated with three different compounds at equivalent, highly effective antisecretory doses. Ranitidine, famotidine and omeprazole at 60, 20 and 40 mg/kg p.o., respectively, inhibited basal acid secretion of chronic gastric fistula rats by greater than 95% and raised intraluminal pH to above 7.0 for 5 hr. The peak plasma gastrin levels associated with each agent were observed 5 hr after dosing. Ranitidine, famotidine and omeprazole induced statistically significant and distinct peak hypergastrinemic responses of 312 +/- 20, 483 +/- 28 and 616 +/- 27 pg/ml, respectively. After 8 hr ranitidine and famotidine associated gastrin values returned to control levels, whereas those of omeprazole remained substantially above control values until the 12th hr. Differences in peak gastrin levels between compounds disappeared at increased dose levels of 500 mg/kg for ranitidine, 200 or 2000 mg/kg for famotidine and 140 mg/kg for omeprazole. Unlike high dose famotidine, omeprazole (140 mg/kg) maintained peak plasma gastrin levels at 8, 12, and 16 hr after dosing. These studies demonstrate clearly hypergastrinemic responses to single dose administration of ranitidine, famotidine and omeprazole. The differences observed in peak plasma gastrin levels at equivalent antisecretory doses of these agents suggests the presence of luminal acid independent components that effect gastrin release. Moreover, these studies indicate that, in the rat, the most unique aspect of omeprazole-associated hypergastrinemia is the magnitude of its prolonged response.