Effect of exogen pentagastrin on mastocyte degranulation, gastric cAMP and intragastric pH in Shay rats.

The degranulation of mastocytes, gastric cAMP and intragastric pH after the administration of 125 micrograms/kg exogen pentagastrin in Shay rats was studied. The results showed a decrease in the number of mastocytes in the gastric mucous membrane in the first hour analysed with a highly significant increase afterwards. There was a significant increase in the values of cAMP which corresponded to an acidification of intragastric pH. From these results it may be deduced that the increase in the release of histamine, as reflected by the decrease in the number of mastocytes, provokes the increase in the gastric levels of cAMP, which would in turn be responsible for the increase in the acid secretion provoked by the administration of exogen pentagastrin.

Effect of pyrenzepine on gastric secretion in Shay rats.

The degranulation of the gastric mastocytes, gastric cAMP levels and intragastric pH were studied in Shay rats after the intraduodenal administration of 20 mg/kg pyrenzepine chlorhydrate. There was a significant increase in the intragastric pH after the administration of this substance, reaching its maximum alkalization 120 min later. The cAMP levels decreased significantly and reached their lowest levels 60 min later. The possible antihistaminic effect of the drug was also studied. Pyrenzepine did not reduce the acid secretion induced by the subcutaneous administration of different doses of histamine. The results show that the decrease in the cAMP gastric levels and in the acid secretion was not due to an antihistaminic effect of pyrenzepine chlorhydrate.

Possible mechanism of stimulation of gastrin secretion by exogenous serotonin in rats.

The effect of 6-hydroxydopamine, propranolol, phentolamine, alpha-methyl-tyrosine and alpha-methyl-tyrosine plus propranolol on serotonin-stimulated gastrin secretion in rats has been examined. Gastrin secretion in response to administration of serotonin alone (10 mg/kg i.p.) was significantly reduced in rats pretreated with 6-hydroxydopamine or with propranolol. These results suggest that the effect of exogenous serotonin on gastrin secretion can be described as sympathomimetic and indirect. The serotonin-stimulated gastrin secretion was significantly enhanced by previous administration of phentolamine. Pretreatment with alpha-methyl-tyrosine also elevated serotonin-stimulated gastrin secretion, indicating that in the presence of diminished concentrations of the catecholamines, the influence of exogenous serotonin on secretion by G cells is increased. This enhancement in the serum gastrin levels was also reduced to a significant extent by simultaneous administration of propranolol, which suggested the activation of G-cell beta-adrenergic receptors after serotonin administration.

Serum gastrin levels during pregnancy.

Serum Gastrin levels were measured by radioimmunoassay in serum samples taken from nongravid normal women and normal healthy pregnant volunteers who were divided into four groups according to gestation time. In nonpregnant control subjects the gastrin values found were 52.23 +/- 2.66 pg/ml. The gastrin levels observed from 5 to 15 and from 36 to 42 weeks of pregnancy are similar to the values of control subjects, whilst the gastrin levels found from 16 to 35 weeks are significantly lower. These results could help us to unravel the distressing problem of dyspeptic symptoms from 16th to 35th week of pregnancy.

Possible central antisecretory action of exogenous serotonin in rats.

The effect of exogenous serotonin (10 mg/kg i. p.) in rats pretreated and unpretreated with 6-hydroxydopamine, propranolol or with alpha-methyltyrosine on intragastric pH was studied. It was observed that after serotonin administration, the intragastric pH increased by approximately five units. The chemical sympathectomy by administration of 6-hydroxydopamine did not alter significantly either basal intragastric pH or the serotonin-induced increase of intragastric pH. The administration of propranolol did not alter significantly the basal intragastric pH, whilst the pretreatment with propranolol abolished the antisecretory effect of serotonin. Repeated dosages with alpha-methyl tyrosine did not alter the basal intragastric pH, but inhibited the effect of serotonin or intragastric pH. These results seem to indicate that the antisecretory effect of exogenous serotonin on gastric acid output, is caused by the inhibition of the vegetative brain centres responsible for the secretory activity of the parietal cells. Furthermore, it is suggested that the antisecretory effect of serotonin is mediated by a release of noradrenaline from the brain adrenergic neurones.

Effect of exogenous serotonin on intragastric pH and its influence on serum gastrin levels in rats.

The effect of various doses of serotonin on the serum gastrin levels and intragastric pH in rats, was studied. After serotonin administration of 10 mg/kg i.p., a significant increase in serum gastrin levels was noted, as well as a strong increase in the intragastric pH. It was also observed that a lower dose, 5 mg/kg i.p., significantly increased serum gastrin levels, while intragastric pH was not affected, remaining at baseline values throughout the study. These results suggest that the increase observed in serum gastrin levels after administration of exogenous serotonin is not mediated by increase in intragastric pH.

Serotoninergic stimulation of gastrin secretion.

The effect of serotonin (10 mg/kg weight) on the gastrin serum levels in rats has been studied. Serum concentrations of gastrin increase significantly from the 56.52 +/- 6.68 pg/ml basal value to 116.87 +/- 3.27 pg/ml at 105 minutes, whereas gastrin in control animals decreases progressively throughout that time. Serum concentration of serotonin was also measured at different times after its administration. An increase to 3.31 +/- 0.6 microgram/ml, maximum value, at 90 minutes was observed anteceding the gastrin peak by 15 minutes.