Inhibitory Action of Omeprazole on Acid Formation in Gastric Glands and on H⁺,K⁺-ATPase Isolated from Human Gastric Mucosa

Abstract

The inhibitory effect of omeprazole on acid formation has been studied in vitro in gastric glands and partly purified H⁺,K⁺-ATPase, prepared from mucosa obtained either from healthy subjects by gastroscopic biopsy or from gastric ulcer patients during antrectomy. The effect of omeprazole was compared with the inhibitory pattern of the H₂-antagonist cimetidine. Acid production in the glands was determined by measuring the accumulation of ¹⁴C-aminopyrine. In glands isolated from patients, omeprazole inhibited acid production maximally stimulated by histamine, db-cAMP, and potassium in a dose-dependent manner, with an IC₅₀ value of about 50 nM irrespective of the agonist used. In contrast, cimetidine inhibited only histamine-induced aminopyrine accumulation, with an IC₅₀ of about 30 μM. The inhibitory effect of omeprazole in db-cAMP-stimulated glands from healthy volunteers was of the same magnitude as seen in glands from gastric ulcer patients. Basal aminopyrine accumulation in glands from both patients and healthy volunteers was almost totally inhibited by omeprazole, whereas cimetidine was without effect. Omeprazole also concentration-dependently inhibited the H⁺,K⁺-ATPase activity in isolated gastric membrane vesicles. The estimated IC₅₀ value was 4 μM.

Key Words:

• Gastric glands
• hydrochloric acid secretion
• omeprazole