Alteration of H2 receptor sensitivity in duodenal ulcer patients after maintenance treatment with an H2 receptor antagonist.

The effects of a specific H2 receptor agonist impromidine, on gastric acid secretion were measured in six patients with duodenal ulcer in clinical remission before and after three months treatment with ranitidine 150 mg nocte. After treatment basal acid output increased from 1.2 to 2.8 mmol/h and after maximal impromidine stimulation from 36.9 (4.7) to 44.2 (6.2) mmol/h (p less than 0.02). Intravenous ranitidine 50 mg was given at the end of the impromidine infusion on each study day; the antisecretory effect of intravenous ranitidine was accentuated after the treatment with ranitidine from a trough acid output of 8.5 (1.2) mmol/h before, to 3.8 (1.5) mmol/h (p less than 0.05) after, treatment. The increased response to the H2 agonist impromidine and the H2 antagonist ranitidine after treatment with ranitidine suggests an enhanced sensitivity of the H2 receptor. This might be explained on the basis of an increase in the number of H2 receptors ('up-regulation').