Effect of acute and chronic acid suppression on plasma gastrin release in the rat.

The mechanisms by which administration of the H+,K(+)-ATPase inhibitor B 831-78 or intragastric perfusion with NaHCO3 induces plasma gastrin release were studied in the rat. Experiments were performed after a washout of residual intragastric contents in fasted animals provided with chronic gastric fistulae. Acute and chronic administration of B 831-78 elevated plasma gastrin dose-dependently up to 5-6 times above control levels, while the increase was only twofold with intragastric NaHCO3 infusion despite similar neutralization of gastric acidity. The profound hypergastrinaemia induced by the H+,K(+)-ATPase inhibitor, after both acute and chronic treatment, was completely prevented or reversed by intragastric perfusion with physiological amounts of acid (0.15 N HCl, 2.5 ml/h). The hypergastrinaemia was, however, largely resistant to high doses of atropine (4.3 mumol/kg) and of the M1 selective muscarinic antagonist telenzepine (10 mumol/kg). In contrast, the modest increase in plasma gastrin induced by gastric perfusion with NaHCO3 was completely suppressed by the high atropine dose and was attenuated by small doses of atropine or telenzepine (0.01 mumol/kg and 1 mumol/kg). These results demonstrate that, in the rat, blockade of the H+,K(+)-ATPase can potently induce gastrin release in the absence of a meal. Moreover, they suggest that interruption of the negative feedback between acid and gastrin release is the main mechanism through which this class of drugs releases gastrin in the rat. Since a similar degree of gastrin release cannot be achieved by alkalinization of gastric contents, additional hormonal or neural regulatory factors may contribute to the drug-induced hypergastrinaemia.