Apparent and intrinsic sensitivity to pentagastrin of acid and pepsin secretion in peptic ulcer.

The sensitivity to stimuli of gastric acid and pepsin secretion in duodenal and gastric ulcer was studied using a pentagastrin dose response that was analyzed by an exponential model. By this model, maximum secretory rate (Vmax), the dose of administered pentagastrin giving 50% of Vmax (D50), and the threshold equivalent dose responsible for basal secretory rate are calculated. Using only individual tests in which the data adequately fitted the model, we report on 171 subjects, 120 with duodenal ulcer, 22 with gastric ulcer, and 29 controls. Among the possible influences on secretion, sex and weight were significant, whereas age and activity or duration of ulcer disease were not. Men secreted more acid per kilogram body weight than women in each group, and men with duodenal ulcer secreted more acid and pepsin than normal men or those with gastric ulcer. Because basal secretion in men with duodenal ulcer was a higher proportion of maximum, D50 (the measure of apparent sensitivity) was 25% lower (p less than 0.01) in patients with duodenal ulcer than in controls; when examined by sex, men with duodenal ulcer had a lower D50 than women with duodenal ulcer, men with gastric ulcer, and male controls. D50 in all patients was very much lower for pepsin than for acid. Km, the dose that would be required to stimulate secretion to 50% of maximum if basal = 0 (intrinsic sensitivity), was not different between groups or sexes. Thus the difference in sensitivity between duodenal ulcer patients and controls was seen only in the apparent, and not in the intrinsic sensitivity indices; this was largely a phenomenon of males and could be explained by a higher ratio of basal to maximal secretion. Neither the observed increase of basal nor the maximal rates of acid and pepsin secretion in duodenal ulcer patients could be explained by an increased sensitivity to gastrin.