Secretory behaviour and histamine formation in the rat Heidenhain pouch following antrectomy

Inhibition by metiamide of secretagogue-induced gastric acid secretion in the conscious Heidenhain pouch rat

1. The inhibition by metiamide of gastric of gastric acid secretion in response to histamine, pentagastrin and bethanechol has been investigated in the conscious Heidenhain pouch rat. 2. Histamine alone stimulated only a low rate of acid secretion. This response was markedly potentiated in the presence of mepyramine. 3. Metiamide at a dose of 0.15 mumole . kg-1 . min-1 I.V. significantly inhibited the acid secretory responses to histamine (in the presence of mepyramine) and pentagastrin. In each case the inhibition of acid output was the result of a significant decrease in both secretory volume and acid concentration. 4. Metiamide at a dose of 0.15 mumole . kg-1 . min-1 I.V. did not inhibit bethanechol-stimulated acid secretion. Increasing the dose of metiamide to 1.0 mumole . kg 1 . min-1 I.V. did produce a significant inhibition. In contrast with histamine and pentagastrin, metiamide inhibited bethanechol-stimulated secretion only by reducing acid concentration; there was no significant decrease in the gastric secretory volume. 5. It is concluded that these results are consistent with the view that histamine and pentagastrin share a common pathway in stimulating gastric acid secretion in the rat. The role of histamine in the control of bethanechol-stimulated acid secretion remains unclear.

Is the basal activity of rat stomach histidine decarboxylase affected by antrectomy?

The serum gastrin concentration and the gastric histidine decarboxylase activity are high in freely fed, unoperated rats but low in antrectomized rats. Following food deprivation the serum gastrin level and the enzyme activity are reduced simultaneously in the unoperated rats. After fasting for 36-48 h - but not before - the enzyme activity drops to the same low levels as in antrectomized rats.

Alterations in secretory patterns following antrectomy in rats with Pavlov pouches

1. In conscious rats provided with Pavlov pouches, with the antrum retained or resected,the gastric secretory response to various stimuli has been studied. Each acid secretory response was related to that obtained with maximal doses of methacholine and histamine in combination, presumed to reflect the maximal secretory capacity of the mucosa. 2. Three weeks after the operation, the maximal acid secretory capacity was 60 percent lower in the antrectomized than in the intact Pavlov pouch rats; the difference was still larger at 6 weeks and 3-5 months, owing to a gradual increase in the rats with the antrum retained. 3. Antrectomy reduced interdigestive secretion of acid to the same degree as the concomitant reduction in maximal secretory capacity. 4. Acid secretion in response to a maximal infusion of pentagastrin was reduced by about 50 percent at 3 and about 65 percent at 6 weeks after antrectomy. No significant difference was, however, noted between the antrectomized and intact rats when the responses were related to the maximal secretory capacity. The dose response curve to pentagastrin revealed a redcued responsiveness to submaximal doses of this agent following antrectomy. 5. The maximal acid secretory response to histamine was reduced after antrectomy, although the sensitivity to submaximal infusions of histamine appeared to be increased. 6. The mean secretroy output to 2-deoxy-D-glucose was reduced by about 65 percent and that to food by about 85 percent following antrectomy. 7. After antrectomy a background infusion of pentagastrin enhanced the secretory responses to 2-deoxy-D-glucose and to food but did not restore the responses to the levels in the intact rats. The feeding responses as related to the maximal secretory capacity were, however, similar in the two groups on infusing pentagastrin in the antrectomized rats. 8. Interdigestive secretion of pepsin was reduced by about 60 percent after antrectomy, while the peak response to 2-deoxy-Dglucose was about twice the interdigestive level in both groups. Pepsin secretion in response to food showed an increased secretion above the interdigestive level of longer duration in the antrectomized than in the intact Pavlov pouch rats. 9. The irreversibily reduced responsiveness of the gastric mucosa after antrectomy is discussed in relation to known morphological and biochemical changes.

Histamine metabolism of the gastric mucosa following antrectomy

1. Histamine metabolism of the gastric mucosa in rats subjected to antrectomy, antrectomy and substitution with pentagastrin and exclusion of the antrum has been investigated employing various in vivo and in vitro methods.2. Mucosal histamine formation after antrectomy fell to about one third, whereas after antrum exclusion histamine formation increased many-fold.3. After antrectomy, mucosal histamine content decreased, and increased after antrum exclusion.4. After total gastrectomy, (a) whole-body histamine formation was reduced to about half, as judged by determining histamine excretion, and (b) pentagastrin infusion did not increase histamine excretion, showing absence of histamine mobilization from extra-gastric sources. In rats with the stomach retained, infusion of pentagastrin induced a dose-dependent increase in histamine excretion.5. Kinetic studies in which [(14)C]histidine was injected and the resulting urinary [(14)C]histamine determined showed that on pentagastrin infusion after antrectomy newly formed histamine was initially mobilized to a larger extent than in the controls.6. Antrectomized rats were subjected to substitution treatment by three injections per day of pentagastrin. After 3 weeks of substitution, histamine excretion was considerably higher than without substitution. After 6 weeks of substitution, histamine excretion was about the same in the substituted antrectomized, non-substituted antrectomized and sham-operated groups. Neither time nor substitution could, however, normalize the excretion of histamine on pentagastrin stimulation after antrectomy.7. In non-substituted antrectomized rats, pentagastrin was less effective in elevating mucosal histamine formation than in the substituted and sham-operated groups.8. The indispensability of the rat in this kind of study is emphasized.

Gastric secretion and its facilitation as related to gastric mucosal histamine

1. In conscious rats provided with Pavlov or Heidenhain pouches the acid and pepsin responses to vagal stimulation, or infusions of gastrin, histamine, methacholine, and to various combinations of these stimulants have been established. The concomitant mobilization and increased formation of gastric mucosal histamine have also been examined.2. Histamine evoked graded acid responses in the Pavlov and Heidenhain pouches. The innervated pouch was more sensitive to histamine than the denervated. Stimulation of pepsin secretion was apparent only in the Heidenhain pouch.3. The acid response to vagal stimulation evoked by 2-deoxy-D-glucose was facilitated by infusion of histamine, but not that of pepsin, the secretion of which was depressed.4. Acid secretion in response to graded infusion of methacholine was enhanced by background infusions of histamine in subthreshold, sub-maximal and maximal dosages.5. The acid response to vagal stimulation was enhanced by a background infusion of gastrin, but not that of pepsin, the secretion of which was depressed.6. A background infusion of a large dose of histamine depressed the maximal acid response to gastrin in both types of pouches.7. Administration of histamine restrained the accelerating effect of gastrin on histidine decarboxylase activity, probably by a feed-back coupling.8. The increase in gastric mucosal histamine, as reflected in its urinary excretion, in response to gastrin infusion was enhanced by vagal stimulation.9. The amounts of histamine that can be mobilized and newly formed in the gastric mucosa have been evaluated and found to be fully adequate for efficient stimulation of the parietal cell.