SUMMARY The effect of intraduodenal acid on pentagastrin-stimulated gastric secretion has been investigated in 12 normal subjects and 23 patients with chronic duodenal ulceration. Plasma secretin levels were monitored during each test using a highly sensitive radioimmunoassay.Significant inhibition of gastric secretion occurred in the normal subjects and duodenal ulcer patients. A significant rise in plasma secretin was observed in both groups after intraduodenal acid though there was a complete lack of correlation between the magnitude of the secretin response and the degree of gastric inhibition. Ten subjects received intraduodenal acid and a subsequent intravenous infusion of exogenous secretin (0.125-0.25 units/kg over six minutes). Gastric inhibition occurred after the acid instillation but not after secretin infusion despite plasma secretin levels greatly in excess of those produced by intraduodenal acid.These results suggest that release of secretin by itself cannot explain the gastric inhibitory response to intraduodenal acid in man.The presence of acid in the duodenum is known to inhibit gastric secretion both in animals (Pincus, Friedman, Thomas, and Rehfuss, 1944;Sircus, 1958) and in man (Shay, Gershon-Cohen, and Fels, 1942;Johnston and Duthie, 1964). The mechanism of this response is, however, uncertain. The main possibilities (which may of course interact) appear to be either a vagal reflex or a humoral response particularly involving secretin. The evidence for each of these views is fully discussed elsewhere (Ward, 1974). The role of the vagus has been examined in detail and it appears likely that gastric inhibition is dependent on a vagal reflex in man (Ward, 1974). Strong claims, however, have been made that in dogs secretin is the mediator of gastric inhibition by intraduodenal acid (Johnson and Grossman, 1968) and the present study was therefore undertaken to examine the response with particular emphasis on the role of secretin.
Materials and MethodsThe response to intraduodenal acid was investigated in 35 patients, 10 of whom also received an intravenous secretin infusion. There were 12 normal subjects (Orm, 2f) and 23 patients (21m, 2f) with chronic duodenal ulceration. The average age of Received for publication 10 July 1974. the normal subjects was 38 years (range 21-63) and their average weight 71 kg (range 55-83 kg). These subjects were awaiting minor inpatient surgery and all were free of gastrointestinal symptoms. The duodenal ulcer patients were awaiting gastric surgery and in all cases the pathology was confirmed subsequently at laparotomy. Their average age was 42 years (range 27-67) and their average weight 68 kg (range 52-82 kg).A duodenal inhibitory test (Ward, 1973) was carried out on each of the normal subjects and duodenal ulcer patients. The gastric stimulus was an intravenous infusion of pentagastrin at a dose rate of 6 ,g/kg/hr. Gastric samples were collected at 10-minute intervals throughout the test.Once a secretory plateau had been reached 40 ml of 0O1N hydrochloric acid ...