Duodenal inhibition of gastric secretion by osmotic agents in normal subjects and patients with duodenal ulcer.
Histamine-stimulated gastric secretion in man is inhibited when the intraduodenal pH is reduced to 2 5 or less (Johnston and Duthie, 1964). The characteristics of the inhibition are these (Fig. 1); the onset is rapid, within two minutes; the degree depends on the potency of the stimulant and inhibitor, but is about 570 in normal subjects when the dose of histamine is 0-2 ,ug./kg./min. and the pH in the duodenum about 14. Inhibition usually ceases promptly when acid perfusion of the duodenum is stopped. The concentration of acid secreted is not affected, the inhibition affecting only the volume and output of acid. The mechanism of this inhibition is not known. The rapid onset and decay which we have noted suggest that nervous reflexes play a part. The evidence from experiments on dogs has been conflicting, Code and Watkinson (1955), Pappas