Bioassay of gastrin using the isolated vascularly perfused rat stomach. A new, simplified and sensitive method

The antiulcer effect of Croton cajucara Benth in normoproteic and malnourished rats

The aim of the present study is to investigate the antiulcerogenic effects of the essential oil (EO) of Croton cajucara Benth in rats fed with a normal protein (NP) and low-protein diet (MN). NP and MN rats were treated with the essential oil for 15 days after chronic ulceration was induced. The EO accelerated healing of acetic acid-induced gastric lesions in NP and MN rats (p<0.05). In a similar experiment on chronic ulceration, Epidermal Growth Factor (EGF) mRNA expression increased in NP rats but not in MN rats. In assays of acute antiulcerogenic activity, C. cajucara increased somatostatin plasma levels and decreased gastrin plasma levels in both animal groups. The EO significantly prevented ethanol-induced gastric ulcers in NP and MN rats (p<0.001). Histological examination showed initial regeneration, formation of inflammatory infiltrate and angiogenesis in the epithelium surface of acetic acid-induced ulcers in NP and MN rats. C. cajucara prevented gastric lesions in both animal groups when ethanol methodology was used. We concluded that the EO showed an antiulcerogenic activity mediated by increased somatostatin secretion and EGF mRNA expression.

Anaesthetic agents inhibit gastrin-stimulated but not basal histamine release from rat stomach ECL cells

By mobilizing histamine in response to gastrin, the ECL cells in the oxyntic mucosa play a key role in the control of the parietal cells and hence of gastric acid secretion. General anaesthesia suppresses basal and gastrin- and histamine-stimulated acid secretion. The present study examines if the effect of anaesthesia on basal and gastrin-stimulated acid secretion is associated with suppressed ECL-cell histamine secretion. A microdialysis probe was implanted in the submucosa of the ventral aspect of the acid-producing part of the stomach (32 rats). Three days later, ECL-cell histamine mobilization was monitored 2 h before and 4 h after the start of intravenous infusion of gastrin (5 nmol kg(-1) h(-1)). The rats were either conscious or anaesthetized. Four commonly used anaesthetic agents were given 1 h before the start of the experiments by intraperitoneal injection: chloral hydrate (300 mg kg(-1)), pentobarbitone (40 mg kg(-1)), urethane (1.5 g kg(-1)) and a mixture of fluanisone/fentanyl/midazolam (15/0.5/7.5 mg kg(-1)). In a parallel series of experiments, basal- and gastrin-induced acid secretion was monitored in six conscious and 25 anaesthetized (see above) chronic gastric fistula rats. All anaesthetic agents lowered gastrin-stimulated acid secretion; also the basal acid output was reduced (fluanisone/fentanyl/midazolam was an exception). Anaesthesia reduced gastrin-stimulated but not basal histamine release by 55 - 80%. The reduction in gastrin-induced acid response (70 - 95%) was strongly correlated to the reduction in gastrin-induced histamine mobilization. The correlation is in line with the view that the reduced acid response to gastrin reflects impaired histamine mobilization. Rat stomach ECL cells were purified by counter-flow elutriation. Gastrin-evoked histamine mobilization from the isolated ECL cells was determined in the absence or presence of anaesthetic agents in the medium. With the exception of urethane, they inhibited gastrin-evoked histamine secretion dose-dependently, indicating a direct effect on the ECL cells. Anaesthetized rats are widely used to study acid secretion and ECL-cell histamine release. The present results illustrate the short-comings of such an approach in that a number of anaesthetic agents were found to impair not only acid secretion but also the secretion of ECL-cell histamine - some acting in a direct manner.

Evaluation of biologic gastrin activity of compound CI-988 in the isolated, vascularly perfused rat stomach

BACKGROUND

The peptoid CI-988 has previously been shown to have high affinity for the cholecystokinin (CCK)-B/gastrin receptor and has been reported to be a powerful CCK antagonist in many systems, although it has agonist activity on histidine decarboxylase in the rat.

METHODS

In the present study the effect of CI-988 on acid secretion and histamine release in the totally isolated, vascularly perfused rat stomach was assessed.

RESULTS

CI-988 was found to be a gastrin agonist with regard to the stimulation of both histamine release and acid secretion.

CONCLUSION

Thus, in this stomach model CI-988 behaved as a CCKB/gastrin agonist. The present study underlines the importance of testing the biologic activity of ligands in models with sufficient sensitivity.

Gastrin stimulates histamine release from the isolated pig stomach

BACKGROUND

Gastrin has been shown to give an immediate and dose-dependent histamine release preceding acid secretion in the totally isolated, vascularly perfused rat stomach.

METHODS

In the present study we prepared isolated, vascularly perfused stomachs taken from pigs and examined the effect of pentagastrin in a concentration of 520 pM on the histamine release to the vascular bed. Pentagastrin was given for three 5-min periods at 10-min intervals, and histamine was determined by a radioimmunoassay method.

RESULTS

Each pentagastrin dose resulted in stimulation of histamine release in the three pig stomachs examined. The various histamine concentrations increased to levels previously shown to stimulate aminopyrine accumulation in isolated pig parietal cells.

CONCLUSION

The present study shows for the first time that gastrin induces histamine release to the vascular bed in the pig, as previously shown for the rat and dog.