Staining of gastrin cells with lead-Haematoxylin.

Fixation of fragments of human antral mucosa with Helly's fluid allows gastrin-containing cells to be identified by an immunofluorescence technique. Lead-Haematoxylin staining carried out on the same sections shows selective reactivity of the immunofluorescent cells. These findings support the identification of gastrin cells with G cells, known from previous studies to react with lead-Haematoxylin.     

ACTH-like immunoreactivity in the gastrin cell. Independent changes in gastrin and ACTH-like immunoreactivity during ontogeny.

Rat antral gastrin cells have been shown to contain ACTH-like immunoreactivity. Studies on the ontogeny of the antral gastrin cells reveal that these cells start to store gastrin before they contain detectable quantities of ACTH-like immunoreactivity. At no stage studied were duodenal gastrin cells found to contain ACTH-like peptides. The data indicate that the G cells synthetizes and/or releases the two hormonal peptides independently.     

Molecular cloning of the human gastrin gene.

A genomic clone that contains the human gastrin gene was isolated from a human gene library. Restriction endonuclease mapping and DNA sequencing analysis revealed that this gene is about 0.7 kb long, and has an intron. The intron is located at a position that separates the coding region into the peptide region essential for biological activities of gastrin and the non-essential, N-terminal peptide region.     

The role of protein kinase C isozymes in bombesin-stimulated gastrin release from human antral gastrin cells.

Two of the most effective stimuli of gastrin release from human antral G cells are bombesin and phorbol esters. Both agonists result in activation of the protein kinase C family of isozymes, however, the exact contribution of protein kinase C to the resultant release of gastrin has been difficult to assess, possibly due to the presence of multiple protein kinase C isozymes in the G cells. The results of the present study demonstrated that the human antral G cells expressed 6 protein kinase C isozymes alpha, gamma, theta, epsilon, zeta, and mu. Of these protein kinase C, gamma and theta were translocated by stimulation of the cells by either 10 nM bombesin or 1 nM phorbol ester. Inhibition of protein kinase Cmu (localized to the Golgi complex) did not decrease bombesin-stimulated gastrin release indicating that this isozyme was not involved in the secretory process. The use of selective antagonists of the calcium-sensitive conventional protein kinase C subgroup resulted in an increase in bombesin-stimulated gastrin release and indicated that protein kinase Cgamma was involved in the desensitization of the bombesin response.     

ACTH-like immunoreactivity in the gastrin cell. Independent changes in gastrin and ACTH-like immunoreactivity during ontogeny

Summary Rat antral gastrin cells have been shown to contain ACTH-like immunoreactivity. Studies on the ontogeny of the antral gastrin cells reveal that these cells start to store gastrin before they contain detectable quantities of ACTH-like immunoreactivity. At no stage studied were duodenal gastrin cells found to contain ACTH-like peptides. The data indicate that the G cells synthetizes and/or releases the two hormonal peptides independently.     

The human gastrin precursor. Characterization of phosphorylated forms and fragments.

There is a potential phosphorylation site in the C-terminal region of the precursor for the acid-stimulating hormone gastrin, which is immediately adjacent to an important cleavage point. In the present study we have sought to identify, separate, quantify and characterize phosphorylated and unphosphorylated forms of human progastrin and its fragments. Identification was made by two radioimmunoassays: (a) a novel assay employing an antibody raised to intact human progastrin; and (b) an assay using antibody reacting with the C-terminal tryptic fragment of human progastrin, as well as progastrin itself. Two forms of human progastrin isolated from a gastrinoma were separated by ion-exchange h.p.l.c., and had similar elution positions on reverse-phase h.p.l.c. and on gel filtration. The more acidic peptide contained close to equimolar amounts of phosphate. On trypsinization, peptides were released that co-eluted on ion-exchange h.p.l.c. with, and had the immunochemical properties of, naturally occurring C-terminal fragments of progastrin. One of the latter was isolated and shown by Edman degradation after derivatization with ethanethiol to have the sequence Ser (P)-Ala-Glu-Asp-Glu-Asn. Similar peptides occur in antral mucosa resected from ulcer patients. The unphosphorylated forms of progastrin predominated, whereas the phosphorylated forms of the C-terminal fragments were predominant. This distribution could be explained by preferential cleavage of phosphorylated progastrin. We conclude that in human progastrin, Ser-96 can occur in the phosphorylated form; this residue immediately follows a pair of basic residues (Arg-Arg) that are cleaved during synthesis of the biologically active product.     

Growth hormone-like immunoreactivity in gastrin cells and gastrinomas.

Growth hormone (GH)-immunoreactive material was found to occur in the antral gastrin cells and in scattered cells of the pancreatic islets in several mammalian species, including man. Examination of gastrinomas revealed the majority of tumour cells to display GH-like immunoreactivity.     

Novel C-terminal gastrin antagonists. Synthesis and biological activity

The C-terminal tetrapeptide, Trp-Met-Asp-Phe-NH2, is a full agonist of gastrin, but des-Phe analogues, including Boc-Trp-Met-Asp-NH2, are antagonists. To ascertain the minimum structural requirement for an antagonist, we used conventional solution phase methodology to synthesize analogues with further modifications including removal of the alpha-amino group of Trp, conversion of the indole to a phenyl ring, and methylation of amide bonds. These analogues were tested for their effect on pentagastrin-stimulated acid release in dogs surgically prepared with a gastric fistula. When infused intravenously at a dose of 20 pmol kg-1 h-1, the peptides significantly inhibited acid secretion. The extent of inhibition ranged from 12% to 60%. Thus, tripeptide analogues based on the C-terminal sequence of gastrin act as potent and specific antagonists of gastrin-stimulated acid secretion.     

Post-translational processing of gastrin in neoplastic human colonic tissues.

Gastrin has been postulated to stimulate proliferation in colorectal neoplasms. Although gastrin mRNA has been demonstrated to be present in colon cancer cell lines, the intact peptide had not been recovered from human colorectal neoplasms. We demonstrate that gastrin and its precursors are present in both colorectal neoplasia and adjacent normal-appearing colonic mucosa. In colonic tissue, the glycine-extended precursor form of the peptide is over 10-fold more abundant than the amidated gastrin, and progastrin is more than 700-fold more abundant. In contrast, amidated gastrin in the human antrum is the predominant form of gastrin by a factor of 10. Furthermore, the ratio of gastrin precursors to gastrin is significantly increased in neoplastic colonic mucosa when compared with normal colonic tissue. These data suggest that the processing of gastrin is unique in the human colon and that further differences in processing occur in neoplastic colonic tissue.     

Hypersecretion of glucagon and gastrin in severely burnt patients.

Hyperglucagonaemia and hypergastrinaemia were observed in some severely burnt patients during their illness. Hyperglucagonaemia seemed to be related to the severity of illness rather than to the burn itself, and the close correlation of glucagon concentrations with glucose and urea and its inverse correlation with bicarbonate concentrations suggest that glucagon might contribute to the hypercatabolic state. One patient developed high levels of gastrin and massive bleeding from a stress ulcer of the duodenum. Possibly gastrin hypersecretion may have a role in the pathogenesis of Curling''s ulcer.     

Rat gastric histamine release: a sensitive gastrin bioassay.

Acid secretion and histamine release from the totally isolated vascularly perfused rat stomach are sensitive parameters for the biological effects of gastrin. By optimalizing the Ca2+ concentration of the vascular perfusate the sensitivity for stimulation of acid secretion was improved from 65 to 16 pmol/l gastrin 1-17 (G-17). Measurement of venous histamine before and after gastrin in each stomach preparation excluded inter-stomach variability and improved the sensitivity to 2 pmol/l G-17. This is the most sensitive gastrin bioassay reported, with a detection limit comparable to that of radioimmunoassay.     

Distribution of gastrin and CCK cells in the rat gastrointestinal tract. Evidence for the occurrence of three distinct cell types storing COOH-terminal gastrin immunoreactivity.

Gastrin and cholecystokinin (CCH) cells of the rat gastrointestinal tract have been studied by immunocytochemistry and radioimmunoanalysis. With antisera directed against the COOH-terminal tetrapeptide sequence, which is common to gastrin and CCK, three distinct endocrine cell types are detected. One of the cell types predominates in the antrum, is scarce in the rest of the gut and corresponds to the gastrin cell. The second cell type is virtually confined to the duodenum and jejunum and corresponds to the CCK cell. The third cell type occurs disseminated in the small intestines, predominates in the ileum, and reacts with COOH-terminus-specific antisera only following diethylpyrocarbonate and not following formaldehyde fixation. It is possible that the third cell type stores a third member of the gastrin-CCK family of gut hormones.