Gastrin I Research Articles

Binding of nicotine to Gastrin I Human studied by fluorescence spectroscopy and nuclear magnetic resonance methods

The interaction between nicotine and Gastrin I Human (GIH) was studied by fluorescence spectroscopy and nuclear magnetic resonance (NMR) methods. Nicotine had little influence on GIH when the ratio of nicotine and GIH was below 80:1. However, with an increasing nicotine concentration, nicotine gradually quenched the intrinsic GIH. NMR showed that nicotine interacted with GIH and the pyrrolidyl ring of nicotine was the major binding function. Hydrogen bonding and van der Waals forces were the major functions in the binding between nicotine and GIH. 3D and synchronous fluorescence studies indicated that GIH emission was primarily attributed to the Trp residues. The results obtained from the present work may be useful to understand the role of nicotine in developing smokeless tobacco products.

Jun and MAP kinases are activated by cholecystokinin in the pancreatic carcinoma cell line KP-1N.

Growth of the human pancreatic carcinoma cell line KP-1N was stimulated with cholecystokinin (CCK)-8. A 40% increase in cell numbers was observed in the presence of 10(-10) MCCK-8 and this increase was inhibited by the addition of 25 microM CCK-A receptor antagonist (CR1505). The binding affinity of CCK-8 to KP-1N cells was 21-fold higher than that of gastrin 17-I. No significant increase in intracellular Ca2+ concentration was found upon stimulation with CCK-8. Components of signal transduction pathways that were activated in KP-1N cells after stimulation with CCK-8 were studied. CCK-8 stimulated tyrosine phosphorylation of a mitogen-activated protein kinase (MAPK) of approximately 42 kDa (p42map). c-Jun amino-terminal kinases (JNKs) of 46 kDa (p46jnk) and 55 kDa (p55jnk) were also activated by CCK-8 and increased the phosphorylation of c-Jun. CCK-8 at 10(-7) M induced 1.5-fold increases in the phosphorylation of MAPK and of c-Jun by JNKs, respectively. These results suggest that cell proliferation stimulated with CCK-8 in KP-1N cells may be mediated by signal transduction cascades leading to activation of JNKs and MAPKs.

Contribution of gastrin to cysteamine-induced gastric acid secretion in rats

The role of circulating gastrin in cysteamine induced gastric acid secretion was examined in conscious male Wistar rats, provided with a portal vein catheter, a jugular vein catheter and a pyloric drainage tube. Intravenous infusion of 0.3 nmol/kg.30 min of gastrin 17-I resulted in serum gastrin concentrations of 1138±151 pg/ml and gastric acid secretion of 104±36 μmol H +/kg.30 min. this acid response was abolished by intravenous injection of 60 μl of a gastrin-antiserum, indicating the efficacy of immunoneutralization with this antiserum in vivo. Intravenous bolus administration of 125 mg/kg of cysteamine induced increases in serum gastrin concentration (864±96 pg/ml) and gastric acid outputs (107±27 μmolH +/kg.30 min) not significantly different from the gastrin 17-I infusion experiments. Gastrin antiserum abolished cysteamine-induced gastric acid secretion, indicating that gastric acid secretion induced by 125 mg/kg of cysteamine is largely mediated by circulating gastrin in rats.

Structure and biological activity of crustacean gastrointestinal peptides identified with antibodies to gastrin/cholecystokinin

Four gastrin/cholecystokinin-like peptides (G/CCK) which cross-react with a specific C-terminal gastrin/CCK antiserum have been isolated from the stomach of the marine crustacean Nephrops norvegicus. The molecular weight of the four peptides was estimated between 1000 and 2000 Da by molecular sieving. By radioimmunoassay, the cross-reactivity of these peptides with human gastrin 17-I was found to be around 0.03%. Pure peptidic fractions were recovered after four successive steps of HPLC. Amino-acid analysis suggested a similarity between the four peptides identified which may belong to a new family. A limited homology between the C-terminus of one Nephrops peptide and vertebrate G/CCK was found after sequenceing. Two of the peptides exhibited secretagogue effects on crustacean isolated midgut glands. The Nephrops peptides, although structurally distinct from the vertebrate G/CCKs, appear to serve similar biological functions in crustaceans.

Elevated gastric acid secretion in patients with Barrett's metaplastic epithelium.

Gastric acid secretion in response to a protein meal and to exogenously administered synthetic human gastrin 17-I was measured in patients with Barrett's esophagus, patients with uncomplicated gastroesophageal reflux, and normal age- and sex-matched controls. Acid secretion, both basally and in response to gastrin 17-I, was significantly greater in patients with Barrett's esophagus compared to normal individuals without reflux. Basal gastrin levels and meal-stimulated levels of the hormone were similar among all three groups. Sensitivity to gastrin, expressed as the concentration causing half-maximal acid secretion, was also similar among the study groups. It is speculated that elevated basal acid production in Barrett's esophagus may contribute to the pathogenesis of the disorder.

Gastrin is not a physiological regulator of pancreatic exocrine secretion in the dog.

The role of gastrin as a regulator of exocrine pancreatic secretion has not been proven adequately. In the present study we therefore compared the relative molar potencies of sulfated and unsulfated gastrin 17 with structurally related CCK peptides (synthetic CCK-8 and natural porcine CCK-33) in stimulating exocrine pancreatic secretion in conscious dogs. Dose response curves were constructed for pancreatic and gastric acid secretion. Plasma gastrin levels after exogenous gastrin 17-I and -II were compared with postprandial gastrin concentrations (meal: ground beef 20 g/kg body wt). The molar potency estimates calculated with synthetic CCK8 as standard (potency = 1.00) for pancreatic protein secretion were natural porcine 50% pure CCK-33 1.60, gastrin 17-I 0.12, and gastrin 17-II 0.16. All four peptides induced a dose-dependent increase in pancreatic bicarbonate output. However, the blood concentrations needed to stimulate pancreatic secretion were above the postprandial gastrin levels. Our data indicate that both gastrin 17 peptides are not physiological regulators of pancreatic enzyme secretion in dogs.

Gastrin receptors in normal and malignant gastrointestinal mucosa: age-associated changes

Synthetic human gastrin 17-I (MG) and an analogue, [Leu15]gastrin-17-I (LG), were radiolabeled with Na125I by Iodo-Gen, EnzymoBead, and chloramine-T methods, and the characteristics of the radiolabeled peptides were determined. When 125I-MG was iodinated by chloramine-T, its biological activity and its binding activity were almost abolished, whereas the biological activity of 125I-LG, iodinated by either of the methods, and of 125I-MG, iodinated by Iodo-Gen and EnzymoBeads, was not significantly affected. The kinetics, affinity, and specificity of binding of 125I-MG, iodinated by Iodo-Gen, to crude and purified membranes from rat fundic mucosa were examined and found to be similar to that for 125I-LG. Age-associated changes in the number and affinity of gastrin receptors (GR) on the crude membranes of gastrointestinal mucosa of rats was also examined. Significantly fewer GR were observed on the crude membranes of fundic mucosa of aged (24 mo old) compared with young (3- and 6-mo-old) rats. In addition, specific gastrin-binding sites (4.7 +/- 0.9 fmol/mg prot) with low affinity (Kd = 3.7 +/- 1.2 nM) were observed in the antrum of aged rats, the significance of which is not understood. There were, however, no differences in the number and characteristics of GR in other regions of the intestine of old and young rats. The presence of GR was additionally assessed in cell lines of gastrointestinal cancers from humans, mice, and hamsters.(ABSTRACT TRUNCATED AT 250 WORDS)

Gastrin receptors on isolated canine parietal cells.

The receptors in the fundic mucosa that mediate gastrin stimulation of acid secretion have been studied. Synthetic human gastrin-17-I (G17) with a leucine substitution in the 15th position ( [Leu15]-G17) was iodinated by chloramine T; high saturable binding was found to enzyme-dispersed canine fundic mucosal cells. 127I-[Leu15]-G17, but not 127I-G17, retained binding potency and biological activity comparable with uniodinated G17. Fundic mucosal cells were separated by size by using an elutriator rotor, and specific 125I-[Leu-15]-G17 binding in the larger cell fractions was highly correlated with the distribution of parietal cells. There was, however, specific gastrin binding in the small cell fractions, not accounted for by parietal cells. Using sequential elutriation and stepwise density gradients, highly enriched parietal and chief cell fractions were prepared; 125I-[Leu15]-G17 binding correlated positively with the parietal cell (r = 0.98) and negatively with chief cell content (r = -0.96). In fractions enriched to 45-65% parietal cells, specific 125I-[Leu15]-G17 binding was rapid, reaching a steady state at 37 degrees C within 30 min. Dissociation was also rapid, with the rate similar after 100-fold dilution or dilution plus excess pentagastrin. At a tracer concentration from 10 to 30 pM, saturable binding was 7.8 +/- 0.8% per 10(6) cells (mean +/- SE) and binding in the presence of excess pentagastrin accounted for 11% of total binding. G17 and carboxyl terminal octapeptide of cholecystokinin (26-33) were equipotent in displacing tracer binding and in stimulating parietal cell function ( [14C]aminopyrine accumulation), whereas the tetrapeptide of gastrin (14-17) had a much lower potency. Proglumide inhibited gastrin binding and selectively inhibited gastrin stimulation of parietal cell function. Canine parietal cells have specific receptors for gastrin that mediate stimulation of parietal cell function. Gastrin receptors were undetectable on chief cells, and yet present on another smaller mucosal cell(s).