Gastrin has two principal biological effects: stimulation of acid secretion from gastric parietal cells and stimulation of mucosal growth in the acid-secreting part of the stomach. Circulating gastrin regulates the increase in acid secretion that occurs during and after meals. Gastrin also stimulates mucosal growth in the stomach. Exogenously administered gastrin causes increased cell division in the proliferative zone that lies between the surface cells and the gastric glands in the acid-secreting mucosa. The newly formed cells undergo differentiation into surface epithelial cells, parietal cells and gastric enterochromaffin-like cells. Furthermore, the increased mucosal proliferation that occurs with refeeding after a period of fasting may be mediated by gastrin since refeeding stimulates gastrin production and a parallel increase in mucosal DNA synthesis. Both food and gastrin cause a rapid increase in cell division and an increase in gastric ornithine decarboxylase mRNA in fasting rats. In preliminary immunoneutralization experiments, the stimulation of ornithine decarboxylase produced by food was inhibited by gastrin antibody. The sustained inhibition of gastric acid secretion obtained by surgery or with antisecretory drug therapy results in hypergastrinaemia associated with increased gastric mucosal cell proliferation. A good correlation between gastric enterochromaffin-like cell density and circulating gastrin concentrations has been found under these conditions as well as during infusions of exogenous gastrin. Trophic effects of gastrin have also been reported for the colon, duodenum and pancreas, but chronic hypergastrinaemia does not appear to produce hyperplasia of these organs. It can be concluded, therefore, that gastrin acts as a physiological stimulant of both gastric acid secretion and gastric mucosal growth and mediates the gastric mucosal proliferation that occurs in response to feeding and hypochlorhydria.

To examine the significance of somatostatin-14 (S-14) and somatostatin-28 (S-28) in gastric physiology, we compared their relative potencies on acid secretion in the dog. On a molar infusion basis, S-14 and S-28 appeared to be equipotent, causing 50% inhibition of peptone meal-stimulated acid secretion at a dose of 400 pmol . kg-1 . h-1. However, comparison of the plasma half lives (t 1/2) of the two peptides revealed that S-28 disappeared at a much slower rate (t 1/2 = 2.84 +/- 0.15 min, mean +/- SE, n = 7) than S-14 (t 1/2 = 0.57 +/- 0.06 min). When acid-inhibitory effect was compared against increment in plasma concentrations produced by peptide infusion, S-14 was roughly 10-fold more potent than S-28. No alteration of gastrin response to peptone was observed at a dose of S-14 or S-28 that completely abolished acid secretion, suggesting that regulation of acid secretion is not mediated by gastrin inhibition. Thus, S-14 is a potent and possibly important physiological inhibitor of gastric acid secretion. Although circulating S-28 may have importance in regulation of some biological functions, it appears to play a less prominent role in regulation of gastric secretion.

To delineate genetic factors involved in the pathogenesis of duodenal ulcer, serum pepsinogen I levels were determined by radioimmunoassay in two large kindreds with multiple members affected with duodenal ulcer. An elevated serum immunoreactive pepsinogen I concentration (greater than 100 ng per milliliter) segregated as an autosomal dominant trait in these families. Furthermore, 10 of 11 patients with clinical ulcer disease in these families had hyperpepsinogenemia. An elevated serum pepsinogen I concentration appears to be a subclinical marker of the ulcer diathesis in families with this autosomal dominant form of peptic-ulcer disease.

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