Histamine is able to suppress the inhibitory effect of somatostatin on exogenous gastrin: comparison between extractive antral histamine and synthetic histamine

The somatostatin/histaminic pathway balance on gastric secretion could be based on a competitive antagonism

Measurements of acid and pepsin secretions and of histamine release in response to food alone or in combination with graded doses of antramine (AH), a molecular form of histamine isolated from antral mucosa, with or without somatostatin were performed simultaneously in dogs equipped with a denervated pouch. AH restored somatostatin-inhibited acid and pepsin secretions but with different intensities in regard to the different inhibitory levels induced by somatostatin. AH competitively antagonized somatostatin (1 microgram/kg/h) inhibition of acid secretion, but when stronger levels of inhibition were achieved, AH restored weakly acid secretion. Recovery of pepsin secretion occurred through a competitive mechanism between AH and somatostatin (1 and 2 micrograms/kg/h). There was a close relationship between the secretory outputs and the integrated histamine responses; the slopes of the regression lines might be considered as reflecting the stimulatory activity of blood histamine on secreting cells. For acid secretion, this activity is similar in control and somatostatin (1 microgram/kg/h) tests, while for pepsin secretion it is identical in control and 1 or 2 micrograms/kg/h somatostatin tests. One can speculate that the suppression of the somatostatin inhibitory effects by antramine, within the limits of physiological conditions, results from a competitive mechanism.

The antigastrinic effect of a phenothiazine (LM 24056) prevents gastric secretory activity of histamine

Gastric antisecretory phenothiazine LM 24056 inhibited acid and pepsin responses to feeding in dogs. Administered perorally two hours before feeding, LM 24056 reduced significantly the secretory responses to combinations of feeding either with antramine, a natural histamine derivate, or with synthetic histamine. LM 24056 reduced circulating gastrin levels (p less than 0.01 and p less than 0.001) and gastrin responses to feeding (p less than 0.01) without modifying neither circulating histamine concentrations nor histamine responses to feeding. The residual acid and pepsin secretions were closely related to gastrin reduction and endogenous or exogenous histamine, by themselves, seemed to be unable to recover the levels of secretory responses observed in response to feeding alone or in combination with antramine or histamine. These data favour a new scheme of gastric secretion regulation where gastrin would be the last step for stimulating parietal and chief cells. LM 24056 by reducing circulating gastrin prevents stimulatory effect of exogenous or feeding-released endogenous histamine. Histamine would not be thus the final common mediator for gastric secretion.

Antramine (antral histamine) antagonizes somatostatin inhibition on endogenous gastrin-induced gastric secretion. A new hypothesis for the role of histamine in gastric secretion regulation

The effects of antramine, an antral histamine (AH), and of synthetic histamine (SH) on acid, pepsin, and gastrin responses to meals alone or in combination with somatostatin were studied in dogs equipped with a Heidenhain pouch. Food-induced acid secretion was potentiated by AH and only slightly increased by SH. Pepsin secretion was increased by AH and decreased by SH. Both AH and SH suppressed the inhibitory activity of somatostatin on food-induced secretion. AH potentiated gastrin response to feeding but decreased it when somatostatin was added to the meal. Since acid secretion was unrelated to gastrin response, it would appear that the secretory effects of AH involve a direct action on secreting cells, itself based on the suppression of somatostatin inhibition. Gastric secretion is probably related to gastrin efficacy on secreting cells, which would result from the antagonistic effects of somatostatin and AH. These data suggest an alternative hypothesis concerning the role of histamine in the control of gastric secretion.

Gastric acid secretion results from antagonistic effects of antral histamine (Antramine) and somatostatin on gastrin

Gastric acid secretion, whole blood histamine concentration and serum gastrin were measured in dogs, equipped with Heidenhain pouch, in response to feeding alone and in combination with antral histamine (AH)--Antramine--or with somatostatin. Feeding stimulated acid secretion, histamine and gastrin responses in a dose-related manner. Addition of antramine to feeding resulted in a potentiated acid and gastrin responses while histamine response corresponded to sum of individual responses to antramine and to feeding. Somatostatin reduced markedly acid and histamine responses, while gastrin response was unchanged. Serum gastrin and whole blood histamine appear to be agonistic factors responsible together for acid secretion. Somatostatin suppresses histamine response and would inhibit gastrin activity on acid secreting cells by this mean. Somatostatin and histamine might act antagonistically on gastrin which would be their common substrate, and thus they could intervene in a regulation process of acid secretion. In regard to synthetic histamine, native antral histamine--antramine--appears to be a better candidate for a physiological histamine regulation of acid secretion.