Birgitta Ryberg

Gastrin stimulates the self-replication rate of enterochromaffinlike cells in the rat stomach: Effects of omeprazole, ranitidine, and gastrin-17 in intact and antrectomized rats

The enterochromaffinlike cells in the rat stomach are rich in histamine and are thought to be under the influence of gastrin. The effect of sustained endogenous and exogenous hypergastrinemia on the activity and proliferation rate of the enterochromaffinlike cells was studied by determining the histidine decarboxylase activity and histamine concentration and by combining histamine immunocytochemistry and autoradiography after in vivo labeling with [3H]thymidine. The proliferation rate of the stem cells in the oxyntic mucosal progenitor zone was also studied. Exogenous hypergastrinemia was induced by infusion of rat gastrin-17 (60 nmol.kg-1.day-1). Endogenous hypergastrinemia was induced by inhibition of gastric acid secretion with omeprazole (80 mumol.kg-1.day-1) or ranitidine (1200 mumol.kg-1.day-1). The effect of omeprazole was also studied in antrectomized rats. In intact rats, all treatments resulted in elevated plasma gastrin levels and were accompanied by an increase in the histidine decarboxylase activity and the histamine content of the oxyntic mucosa. This resulted in an increase in the enterochromaffinlike cell proliferation rate, leading to enterochromaffinlike cell hyperplasia. The number of labeled stem cells was increased, but this effect was not as pronounced as in the enterochromaffinlike cells. In antrectomized rats, the inhibition of acid secretion by omeprazole did not result in elevated plasma gastrin or in an increase in the activity or number of enterochromaffinlike cells, indicating that omeprazole per se had no effect on these cells. These data support the view that gastrin stimulates the proliferation rate of both enterochromaffinlike cells and stem cells. Gastrin also stimulates the activity of the enterochromaffinlike cells.

Trophic effects of continuous infusion of [Leu15]-gastrin-17 in the rat

This report describes the trophic effects of exogenous gastrin on the digestive tract and pancreas and the effect on the density of enterochromaffinlike cells in the oxyntic mucosa of the stomach. Female rats were given 1.2 or 2.4 nmol/kg.h of synthetic human [Leu15]-gastrin-17 for 28 days (via osmotic minipumps implanted subcutaneously). As a result, measurable plasma gastrin increased from about 230 pg/ml in the controls to about 500 and 800 pg/ml in the low- and high-dose groups, respectively. The trophic effects of gastrin were reflected in increased stomach weight and oxyntic mucosal mass. Gastrin also increased the enterochromaffinlike cell density and associated parameters (histamine concentration and histidine decarboxylase activity) but was without demonstrable effects on other parts of the digestive tract and pancreas. The results show that continuous infusion of exogenous gastrin for 28 days induces trophic changes similar to those seen after a period of hypergastrinemia induced by treatment with effective inhibitors of acid secretion.

Hypergastrinaemia produces trophic effects in stomach but not in pancreas and intestines

Hypo- or anacidity, caused by antisecretagogues, stimulates gastrin release and leads to hypergastrinaemia. If drug treatment is maintained over a period of time, the hypergastrinaemia can be expected to give rise to trophic effects. We examined the trophic consequences of the very marked hypergastrinaemia produced by long-term treatment (16-20 weeks) of rats with large doses of the substituted benzimidazole, omeprazole, a potent and long-acting blocker of acid secretion. The weight of the stomach and the oxyntic mucosal thickness were increased, whereas the weight of the pancreas and the intestines and the thickness of the mucosa of the antrum and small and large intestine were unaffected. The number of exocrine cells (parietal, zymogen and mucous cells) were uniformly increased by 25-30%. The density of parietal and zymogen cells, expressed as number of cell nuclei per mm2 epithelium, was unchanged. The volume density of parietal cells, expressed as % of epithelial volume, was also unchanged, implying that the volume of the individual parietal cell had not increased. The density of endocrine ECL cells in the stomach increased 5-fold. Thus, the findings demonstrate a growth-promoting effect of the hypergastrinaemia on the oxyntic mucosa, the ECL cells in particular, and the lack of such an effect on the antrum, pancreas and intestines.

Omeprazole and ranitidine, antisecretagogues with different modes of action, are equally effective in causing hyperplasia of enterochromaffin-like cells in rat stomach

Female rats were treated for 28 days with high doses of the gastric acid secretion inhibitors omeprazole and ranitidine. Omeprazole, which is long-acting, was given orally once daily. Ranitidine, which is short-acting, was given by continuous infusion (via osmotic minipumps, implanted subcutaneously). The aim was to produce a similar degree of acid inhibition with the two drugs. The inhibition of acid secretion over the day and night was more pronounced in the omeprazole-treated rats (maximal inhibition 100%, minimum 85%) than in those receiving ranitidine (mean 70%). In both groups, there was a great increase in plasma gastrin, somewhat greater after omeprazole than after ranitidine. The gastrin concentration in the antrum was almost doubled by both treatments and there was a moderate increase in the number of antral gastrin cells in the omeprazole-treated rats. The number of enterochromaffin-like (ECL) cells (per visual field) increased in the oxyntic mucosa to the same extent (greater than 100%) in the ranitidine- and omeprazole-treated rats. Apart from the gastrin cells in the antrum and the ECL cells in the corpus no other gastric endocrine cell type seemed to respond to treatments with antisecretagogues. We conclude that, regardless of the type of antisecretagogue used, effective and long-term suppression of gastric acid secretion results in sustained hypergastrinemia and increased number of ECL cells. Conceivably therefore, the ECL cell hyperplasia reflects the trophic effect of gastrin.

Omeprazole: Its Influence on Gastric Acid Secretion, Gastrin and ECL Cells*

The H+,K+-ATPase inhibitor omeprazole is a highly effective gastric antisecretory agent, both in animals and man, with a long duration of action. These properties are shared by a number of recently described histamine H2-receptor antagonists. In life-long oncogenicity studies of these H2-receptor antagonists, as well as with the H+,K+-ATPase inhibitor omeprazole, gastric enterochromaffin-like cell (ECL cell) hyperplasia and carcinoids have been found. The purpose of this paper is to summarize available evidence for the “Gastrin Hypothesis” to explain the development of ECL-cell hyperplasia. The hypothesis may be outlined as follows: 1) Inhibition of gastric acid secretion leads to elevated antral pH and, secondarily, to release of gastrin from the antral gastrin cells into the blood stream. 2) Gastrin causes both general hypertrophy of the oxyntic mucosa and hyperplasia of the ECL cells in the oxyntic mucosa. That this sequence of events occurs not only with omeprazole but also with other effective gastric antisecretory agents has been verified in the rat by giving the H2-receptor antagonist ranitidine as a continuous infusion. Ranitidine caused a hypergastrinemia of a similar magnitude as that seen after omeprazole, provided that the acid secretion was inhibited to a similar degree. At similar gastrin levels, ECL-cell hyperplasia of the same magnitude developed during both ranitidine and omeprazole treatment. Antrectomy prevented the development of ECL-cell hyperplasia during omeprazole treatment, indicating that the hyperplasia was not due to the drug treatment per se, but rather to the hypergastrinemia. Both the hypergastrinemia and the ECL-cell hyperplasia were found to be reversible. Control plasma gastrin levels were reached within a few days of stopping long-term treatment, and the ECL-cell density was back to normal 20 weeks after discontinuing 10 weeks of treatment with high-dose omeprazole. We conclude from these studies that the ECL-cell hyperplasia seen in rats after long-term treatment with gastric acid secretion inhibitors is reversible and secondary to the hypergastrinemia, and is not caused by the drugs per se. Furthermore, although the gastrin mechanism for the regulation of the ECL cells seems to be similar in different species, there are quantitative differences with regard to the ECL-cell density and possibly also the sensitivity of ECL cells to gastrin.

Effects of Partial Resection of Acid-Secreting Mucosa on Plasma Gastrin and Enterochromaffin-Like Cells in the Rat Stomach

Female rats were subjected to various degrees (50, 75, 90 and 100%) of fundectomy, i.e. resection of the acid-producing part of the stomach, to compare the effects of different degrees of reduction of the amount of acid reaching the antrum. Plasma gastrin was monitored for 10 weeks after the operation. Histidine decarboxylase (HDC) activity, histamine concentration and density of enterochromaffin-like (ECL) cells in the remaining oxyntic mucosa were determined in the rats subjected to 50 or 75% fundectomy. There was a close correlation between the amount of acid-producing mucosa removed and the plasma gastrin levels, the highest gastrin level being observed in the rats subjected to 100% fundectomy. HDC activity, histamine concentration and ECL cell density seemed to reflect plasma gastrin concentration. These findings indicate that hypergastrinemia induced by surgical removal of acid-producing mucosa in the rat has the same effects on oxyntical mucosal HDC activity, histamine concentration and ECL cell density as hypergastrinemia induced by continuous gastrin infusion or by long-term treatment with effective antisecretagogues.

Effects of Omeprazole and Ranitidine on Gastric Acid Secretion, Blood Gastrin Levels and [3H]-Thymidine Incorporation in the Oxyntic Mucosa from Dogs and Rats

Dogs provided with a gastric fistula were treated orally for 1 week either with the H+, K+-ATPase inhibitor omeprazole, 80 mumol/kg once daily, or with the histamine H2 receptor antagonist ranitidine, 85-175 mumol/kg every 8 h. Acid secretion, serum gastrin levels and [3H]-thymidine incorporation in the corpus mucosa were determined before, during and after the treatment period. In order to examine differences between species, plasma gastrin levels and [3H]-thymidine incorporation in the oxyntic mucosa were also determined in female rats treated up to 1 week with omeprazole, 400 mumol/kg orally once daily. Histamine-stimulated gastric acid secretion in dogs treated with omeprazole or ranitidine was almost completely inhibited during the whole treatment period. As a consequence of that, the meal-stimulated gastrin levels were increased (7-fold) during treatment by both compounds. [3H]-thymidine incorporation in the dog corpus mucosa was increased approximately 4 times on day 5 both with omeprazole and ranitidine. After the treatment was stopped, gastric acid secretion, serum levels of gastrin and the rate of [3H]-thymidine incorporation were back to control level in both groups within 11 days. In the rats, the plasma gastrin levels increased 10-fold and the rate of [3H]-thymidine incorporation in the corpus mucosa increased 3-fold during treatment with omeprazole. In conclusion, a pronounced suppression of gastric acid secretion over the day with antisecretagogues results in hypergastrinemia in both dogs and rats. As a consequence of the trophic effect of gastrin, the incorporation of [3H]-thymidine in the oxyntic mucosa is increased.(ABSTRACT TRUNCATED AT 250 WORDS)

Hyperplasia of histamine-depleted enterochromaffinlike cells in rat stomach using omeprazole and α-fluoromethylhistidine

In the rat, gastric histamine is stored mainly in the enterochromaffinlike cells. Gastrin releases histamine from these cells, and long-term hypergastrinemia results in hyperplasia. The effect of sustained hypergastrinemia on histamine-depleted enterochromaffinlike cells was studied by measuring histidine decarboxylase activity and histamine concentrations and by using quantitative histology. Hypergastrinemia maintained for 6 weeks was induced by inhibition of gastric acid secretion with omeprazole (400 mumol.kg-1.day-1) given orally, and histamine synthesis was inhibited for the same length of time with alpha-fluoromethylhistidine (3 mg.kg-1.h-1) given via osmotic minipumps. In rats given omeprazole alone, the effects of the resulting hypergastrinemia on the enterochromaffinlike cells was reflected in increased histidine decarboxylase activity, increased histamine concentration, and increased number of enterochromaffinlike cells. The general trophic effects on the stomach were seen as increased stomach and oxyntic mucosal weight and increased mucosal thickness. Treatment with alpha-fluoromethylhistidine plus omeprazole markedly reduced the histidine decarboxylase activity and histamine concentration, but the weight of the stomach and oxyntic mucosa, the enterochromaffinlike cell density, and intensity of histidine decarboxylase immunostaining were increased to at least the same extent as after omeprazole alone. These observations indicate that enterochromaffinlike cell histamine is not important for a full expression of gastrin-evoked trophic effects in the stomach.

Intraocular transplants of a human gastrinoma in immuno-suppressed rats: morphological, chromatographic and functional studies

Tissue pieces of a metastatic human gastrinoma (ultrastructural Type II) were successfully transplanted to the anterior eye-chamber of rats immunosuppressed with Cyclosporin A. Immunocytochemical investigation of the transplants showed evidence for preserved endocrine activity of tumour cells with immunoreactivity towards the C-terminal of the gastrin/cholecystokinin molecule. Studies of gastric acid secretion in tumour-bearing rats and sham-operated controls with chronic gastric fistulas showed that the basal acid output did not differ between the groups during 3 weeks of study. However, the stimulated gastric acid secretion decreased after 5 days in both groups to remain significantly depressed throughout the study, an effect probably due to Cyclosporin A treatment of the groups. The concentration of immunoreactive gastrin in plasma from rats with tumours in oculo was 5 times higher than in sham-operated rats. Gastrin-34 was the major immunoreactive component in both patient serum and rat plasma. An immunoreactive fraction corresponding to component I was found in the patient serum, but not in the rat plasma, although present in the chamber fluid. Components corresponding to gastrin-17 were found both in the patient serum and in the rat plasma. The chromatographic pattern of the tumour was similar to that in rat chamber fluid. The dominating component corresponded to gastrin-17, while gastrin-34 represented the quantitatively smaller component. Gastrin-34 was, however, relatively more abundant in the tumour extract than in the chamber fluid. The study also indicates that a gastrin-producing tumour transplanted in oculo in immunosuppressed rats may increase the rat plasma concentration of the same molecular forms of gastrin as seen in the clinical situation.

Gastrin and somatostatin in the rat antrum. The effect of removal of acid-secreting mucosa

Female rats were subjected to operations aimed at reducing the amount of oxyntic gland mucosa draining its acid secretion to the antrum. The rats were provided either with Heidenhain or Pavlov pouches reducing the oxyntic mucosa draining its secretion to the antrum by about 50% or subjected to various degrees (75, 90 and 100%) of fundectomy. Ten weeks following surgery, plasma levels of gastrin and somatostatin were assayed. At the same time, antral mucosal content of gastrin and somatostatin was determined as well as the mucosal density of these hormone-producing cells. There was a relationship between the amount of acid-secreting mucosa removed and the ensuring plasma concentration of gastrin. Thus, a stepwise increase in plasma gastrin was found with the highest levels obtained in rats subjected to 90 or 100% fundectomy. The somatostatin concentration in plasma was reduced only in rats subjected to fundectomy with the most sustained decrease in animals in which all oxyntic gland mucosa had been removed. There was also a relationship between the amount of acid-secreting mucosa removed and the gastrin content of the antral mucosa. An inverse relationship seemed to exist between antral gastrin and somatostatin concentrations. However, a significant decrease in somatostatin concentration of the antral mucosa was seen only in rats subjected to a fundectomy. The number of gastrin cells in the antral mucosa was increased in fundectomized rats only, with the largest density seen in rats deprived of all oxyntic mucosa. A corresponding decrease in the number of somatostatin cells was noticed. Our results would suggest an apparent functional relationship between antral gastrin and somatostatin cells, where the antral acid load (or pH) appears to be the major factor of physiological significance.