Gastrin response to candidate messengers in intact conscious rats monitored by antrum microdialysis

We monitored gastrin release in response to locally applied candidate messengers in intact conscious rats. Earlier studies have been performed on anaesthetized animals, isolated pieces of antrum, or purified preparations of gastrin cells. In this study we created an experimental situation to resemble physiological conditions, using reverse microdialysis to administer regulatory peptides and amines that might affect gastrin secretion. Microdialysis probes were implanted in the submucosa of the antrum of the rat stomach. Three days later, putative messenger compounds were administered via the probe. Their effects on basal (24h fast) and omeprazole-stimulated (400μmol/kg/day, 4days peroral administration) gastrin release were monitored by continuous measurement (3h) of gastrin in the perfusate (radioimmunoassay). Fasted rats (low microdialysate gastrin, 2.1±0.1pmoll−1) were used to study stimulation of gastrin release. Omeprazole-treated rats (high microdialysate gastrin, 95.8±6.7pmoll−1) were used to study suppression of gastrin release. The following agents raised the concentration of microdialysate gastrin (peak response): gastrin-releasing peptide (GRP) (11-fold increase at a near-maximal dose), carbachol (5-fold increase), serotonin (2-fold increase) and isoprenaline (20-fold increase). Adrenaline and noradrenaline induced transient but powerful elevation (40- and 20-fold increase). Somatostatin, galanin and bradykinin (at near-maximal doses) suppressed omeprazole-stimulated gastrin release (50% decrease). Calcitonin gene-related peptide, ghrelin, gastric inhibitory peptide, motilin, neurotensin, neuromedin U-25, peptide YY and vasoactive intestinal peptide were without effect on gastrin release, as were aspartate, γ-aminobutyric acid, glutamate, glycine, dopamine and histamine. The results support the view that G cells operate under neurocrine/paracrine control. They were stimulated by agents present in enteric neurons (GRP, galanin, choline ester and catechol amines) and in gastric endocrine cells (serotonin). They were inhibited by somatostatin (D cell peptide), galanin (neuropeptide) and by the inflammatory agent bradykinin.