Histamine storage and formation in canine gastric mucosa--effect of pentagastrin stimulation

Somatostatin inhibits gastrin-induced histamine secretion and synthesis in the rat

Somatostatin is a potent inhibitor of gastric acid secretion. However, the effect of somatostatin on gastric histamine secretion and synthesis has not been well understood, despite the fact that histamine plays a key role in the regulation of gastric acid secretion. This study was designed to determine the effect of somatostatin on gastric histamine mobilization and acid secretion in conscious rats. In conscious rats with a gastric fistula, a 4 h intravenous infusion of gastrin-17 I (1 nmol/kg/h) evoked a marked increase in fundic histidine decarboxylase activity (the sole histamine-forming enzyme) and reduced fundic histamine content with a concomitant increase in gastric acid secretion. Somatostatin-14 (10 nmol/kg/h) significantly inhibited gastrin-induced gastric acid secretion and fundic histidine decarboxylase activity and prevented a gastrin-induced decrease in fundic histamine content. In conscious rats with a vesical fistula, somatostatin-14 (10 nmol/kg/h) significantly inhibited the urinary histamine excretion induced by a gastrin-17 I (1 nmol/kg/h) infusion. These findings suggest that the inhibitory action of somatostatin on gastrin-induced acid secretion is mediated by the inhibition of histamine mobilization.

Studies of isolated parietal and enterochromaffin-like cells from the rat

Rat gastric mucosal cells isolated by enzyme dispersion were separated by elutriation centrifugation. The amount of histamine and the number of enterochromaffin-like (ECL) cells and parietal cells were determined in the crude mucosal cells and the various elutriation fractions. The mucosal cells contained 2.6% ECL and 20% parietal cells. Elutriation centrifugation resulted in good separation of parietal cells and ECL cells. Most of the ECL cells were elutriated in the small cell fractions. Scattered ECL cells were also present in the fraction enriched with parietal cells. Histamine and carbacholine stimulated aminopyrine uptake in a concentration-dependent manner with about the same efficacy, 5.6 times the base-line value. When combined with the phosphodiesterase inhibitor isobutyl methylxanthine, the maximal histamine stimulation was increased to 16.8 times the base-line value, and the sensitivity increased about 10-fold. Gastrin at high and unphysiologic concentrations stimulated only faintly the aminopyrine uptake in parietal cells and the histamine release from ECL cells.

Effect of cholecystokinin receptor antagonists, MK-329 and L-365,260, on cholecystokinin-induced acid secretion and histidine decarboxylase activity in the rat

To elucidate the regulatory mechanism of acid secretion by cholecystokinin (CCK) in vivo, we compared the effects of CCK and gastrin on acid secretion and histidine decarboxylase (HDC) activity. We also examined the effects of MK-329, a specific antagonist for pancreatic-type CCK receptor, and L-365,260, a specific antagonist for gastrin-type CCK receptor, on the action of CCK. Graded doses of CCK or gastrin were intravenously infused into conscious rats with gastric fistula. Gastrin-17 I infusion up to 10 nmol/kg/h resulted in dose-related increases in acid secretion. CCK-8 infusion also caused an increase in acid secretion. However, it reached a peak with 0.3 nmol/kg/h CCK-8 and attenuated with higher concentrations of CCK-8. This attenuating effect of a higher dose of CCK was reversed by MK-329, but not by L-365,260. Both CCK and gastrin were potent in increasing fundic HDC activity, and the effect of CCK on HDC activity was significantly inhibited by L-365,260, but not by MK-329. Taken together, the present study suggests that CCK and gastrin stimulate histamine formation via a gastrin-type CCK receptor, and the attenuating action of CCK with higher concentrations on acid secretion in vivo is mediated by a pancreatic-type CCK receptor.

Effects of some gastrointestinal peptides on isolated human and rabbit gastric glands

The isolated gastric gland preparation, with aminopyrine accumulation as an index of the parietal cell response, has been used to study the effects of somatostatin (S-14), gastrin-releasing peptide (GRP), cholecystokinin (CCK-8), vasoactive intestinal peptide (VIP), and peptide YY (PYY) on the in vitro acid secretion in human and rabbit oxyntic mucosa. Somatostatin was able to inhibit the parietal cell response to histamine in both human and rabbit isolated gastric glands (maximal inhibition, 22% and 34%, respectively) but failed to inhibit the parietal cell response to db-cAMP. However, other peptides capable of inhibiting gastric acid secretion in vivo, such as CCK, VIP, and PYY, were unable to induce any inhibition of the parietal cell response to db-cAMP or histamine in the isolated gastric gland preparation irrespective of the species studied. GRP was not able to induce a parietal cell response, a finding that is in accord with the assumption that the stimulatory effect of GRP on gastric acid secretion in vivo is by releasing gastrin from antral G-cells.

Visualisation of the gastrin receptor within rat mucosa using a biotinylated gastrin antagonist

We have previously demonstrated that the peptide Boc-L-Trp-L-Leu-beta-Ala is a potent and specific antagonist of pentagastrin-stimulated acid secretion in both the rat and the dog. Using conventional solution phase methodology, the analogue biotinyl-L-Trp-L-Leu-beta-Ala was prepared in reasonable yield and purity and applied to cryostat sections of rat intestinal and other tissues. The sections were exposed to 5-10 micrograms of peptide and the bound analogue was visualised using streptavidin-fluorescein. The binding of the analogue was demonstrated in sections from fundus, duodenum, ileum, colon, and lung. However, the analogue failed to bind to tissue from the pancreas, heart, kidney, or liver. The binding of the probe was greatly reduced or completely inhibited by preincubation with Boc-L-Trp-L-Leu-beta-Ala, pentagastrin, or gastrin 1-17. The distribution of the cells recognised by the probe was consistent with the distribution of histamine-containing enterochromaffin-like cells. The results of this study may have some bearing on current theories of the mechanism of gastrin-stimulated acid release.

Histamine metabolism in human gastric mucosa. Effect of pentagastrin stimulation

The metabolism of histamine in the human gastric mucosa was studied in the basal state and during pentagastrin stimulation. Studies were made in healthy volunteers and in patients with peptic ulcer disease. Mucosal biopsies were taken from antral and oxyntic gland areas whereupon histamine content, histidine decarboxylase activity, and histamine methyltransferase activity were simultaneously assayed. Histamine content of the oxyntic gland mucosa was decreased as a consequence of pentagastrin administration in all groups studied, and this decrease was numerically largest in patients with duodenal ulcer disease. Pentagastrin induced a significant increase in histidine decarboxylase activity of the oxyntic gland mucosa with the most profound increase seen in patients with duodenal ulcer. The highest rates of histamine formation were present in the oxyntic mucosa of patients with Zollinger-Ellison syndrome. The activity of histamine methyltransferase was the same in all groups studied and was not changed by pentagastrin. In conclusion, pentagastrin administration in humans is followed by a significant mobilization of histamine only from the oxyntic gland mucosa, an effect that is more pronounced in patients with duodenal ulcer disease.

Histamine metabolism of the human gastric mucosa--a study on the regional distribution of the amine and enzyme activities

Histamine content, histidine decarboxylase activity and histamine methyl transferase activity of the human gastric mucosa have been studied in healthy subjects. Histamine content was evenly distributed over the gastric mucosa and no significant difference could be observed between the oxyntic and pyloric gland area. A 'specific' histidine decarboxylase was found in the human gastric mucosa and the enzyme activity was significantly higher in the corpus compared to the antral mucosa. We found no difference in enzyme activity of the mucosa obtained from three defined areas of the corpus region of the stomach. Histamine methyl transferase activity was of the same magnitude in the corpus as in the antral mucosa. In addition, with regard to histamine methyl transferase activity, we were unable to demonstrate any difference in activity in the mucosal specimens obtained from the defined areas of the stomach. The presented technique to obtain gastric mucosal tissue specimens during routine fibreoptic endoscopy of the stomach, allows studies over gastric mucosal histamine metabolism in health as well as in disease states.