Achlorhydria induced changes in gastrin, somatostatin, H+/K(+)-ATPase and carbonic anhydrase in the sheep.

Gastrin, somatostatin, H+/K(+)-ATPase and carbonic anhydrase are principal elements of acid secretion. We investigated in the conscious sheep the effect of 24 h omeprazole (an H+/K(+)-ATPase inhibitor) infusion on these elements at the level of synthesis, storage and secretion. Omeprazole inhibited acid secretion-pH increased from 3.0 to 7.1 at 24 h. Plasma amidated and glycine extended gastrin increased 3-fold while the ratio of amidated to glycine extended gastrins (4:1) remained unchanged. Despite the increase in circulating gastrin, antral gastrin concentration and mRNA did not change significantly. Gastrin-17 (amidated and glycine extended) was the predominant form in the circulation and antrum, although there were preferential increases in larger forms following omeprazole treatment. Omeprazole had no effect on somatostatin mRNA or peptide levels in the fundus. Similarly, plasma somatostatin remained unchanged. However, antral somatostatin increased significantly (63%) following omeprazole treatment accompanied by a 4-fold increase in its mRNA. Fundic H+/K(+)-ATPase mRNA was unchanged but a significant increase (87%) in carbonic anhydrase II mRNA was observed. Omeprazole induced hypergastrinaemia occurred without a measurable reduction in storage or increased synthesis of gastrin at 24 h. Increased antral somatostatin synthesis and storage may result from stimulation by plasma gastrin on antral D cells, independent of acid. The rise in carbonic anhydrase II mRNA in the absence of any change in H+/K(+)-ATPase mRNA may reflect the differential sensitivity of the genes encoding these two enzymes to the stimulatory action of gastrin.