Inhibition of gastrin gene expression by somatostatin

Dissecting carboxypeptidase E: properties, functions and pathophysiological roles in disease

Since discovery in 1982, carboxypeptidase E (CPE) has been shown to be involved in the biosynthesis of a wide range of neuropeptides and peptide hormones in endocrine tissues, and in the nervous system. This protein is produced from pro-CPE and exists in soluble and membrane forms. Membrane CPE mediates the targeting of prohormones to the regulated secretory pathway, while soluble CPE acts as an exopeptidase and cleaves C-terminal basic residues from peptide intermediates to generate bioactive peptides. CPE also participates in protein internalization, vesicle transport and regulation of signaling pathways. Therefore, in two types of CPE mutant mice, Cpe^fat/Cpe^fat and Cpe knockout, loss of normal CPE leads to a lot of disorders, including diabetes, hyperproinsulinemia, low bone mineral density and deficits in learning and memory. In addition, the potential roles of CPE and ΔN-CPE, an N-terminal truncated form, in tumorigenesis and diagnosis were also addressed. Herein, we focus on dissecting the pathophysiological roles of CPE in the endocrine and nervous systems, and related diseases.

Transcriptome analysis of the duodenum, pancreas, liver, and muscle from diabetic Goto-Kakizaki rats fed a trypsin inhibitor derived from squid viscera

Trypsin inhibitors (TIs) have various nutritional effects. However, a detailed mechanism for their effects, especially on the gene expression patterns in various tissues, remains unknown. Here, we used transcriptome techniques and gene ontology (GO) analysis to examine the effects of squid TI (sqTI), a biochemically stable peptide, on diabetic Goto-Kakizaki rats after feeding for 10 weeks. We demonstrated that downregulation of SREBP1c in the liver via duodenal/pancreatic hormones suppresses the blood cholesterol level. Consistently, in GO analysis, the term "cholesterol biosynthetic process" was enriched among downregulated genes. No hypoglycemic or insulinotropic effects were observed, in contrast to the results from our previous studies (single stimulation with the same dose of TI), which can be partly ascribed to the inactive responses of the duodenum and pancreas in this condition.

False-positive secretin stimulation test for gastrinoma associated with the use of proton pump inhibitor therapy

We report the case of a 22-year-old woman who was referred for evaluation of possible Zollinger-Ellison syndrome because of hypergastrinemia and a positive secretin stimulation test. She was being treated with proton pump inhibitors (PPIs) for severe gastroesophageal reflux disease during her initial evaluation. At cessation of PPI therapy, her fasting serum gastrin levels normalized, as did her response to secretin injection. Previous reports describing false-positive secretin tests have been limited to cases of hypergastrinemia in the setting of chronic atrophic gastritis, presumably a result of achlorhydria. This case represents a clearly documented instance of PPI-related hypergastrinemia with a false-positive secretin test, with subsequent normalization of serum gastrin and a negative secretin test after withdrawal of PPI therapy. The current case emphasizes the need to assess the acid secretory status of individuals with hypergastrinemia and to discontinue the use of potent antisecretory agents, principally PPIs, to avoid the erroneous diagnosis of gastrinoma and before embarking on expensive and potentially invasive evaluations for the purpose of tumor localization.

Peripheral PACAP inhibits gastric acid secretion through somatostatin release in mice

1. Studies in rats suggest that PACAP modulates gastric acid secretion through the release of both histamine and somatostatin. 2. We characterized the effects of exogenous PACAP on gastric acid secretion in urethane-anesthetized mice implanted with a gastric cannula and in conscious 2-h pylorus ligated mice, and determined the involvement of somatostatin and somatostatin receptor type 2 (SSTR2) by using somatostatin immunoneutralization, the SSTR2 antagonist, PRL-2903, and SSTR2 knockout mice. 3. Urethane-anesthetized wild-type mice had low basal acid secretion (0.10+/-0.01 micromol (10 min)(-1)) compared with SSTR2 knockout mice (0.93+/-0.07 micromol (10 min)(-1)). Somatostatin antibody and PRL-2903 increased basal secretion in wild-type mice but not in SSTR2 knockout animals. 4. In wild-type urethane-anesthetized mice, PACAP-38 (3-270 microg kg(-1) h(-1)) did not affect the low basal acid secretion, but inhibited the acid response to pentagastrin, histamine, and bethanechol. 5. In wild-type urethane-anesthetized mice pretreated with somatostatin antibody or PRL-2903 and in SSTR2 knockout mice, peripheral infusion of PACAP-38 or somatostatin-14 did not inhibit the increased basal gastric acid secretion. 6. In conscious wild-type mice, but not in SSTR2 knockout mice, PACAP-38 inhibited gastric acid secretion induced by 2-h pylorus ligation. The antisecretory effect of PACAP-38 was prevented by immunoneutralization of somatostatin. 7. These results indicate that, in mice, peripheral PACAP inhibits gastric acid secretion through the release of somatostatin and the activation of SSTR2 receptors. There is no evidence for stimulatory effects of PACAP on acid secretion in mice.

Carboxypeptidase E in rat antropyloric mucosa: distribution in progenitor and mature endocrine cell types

Processing of most gut hormones involves cleavage between dibasic amino acids followed by carboxypeptidase-catalyzed removal of the COOH-terminal basic residue, resulting in peptides with a COOH-terminal glycine. Such peptides may subsequently be converted to amidated peptides or can be directly secreted. It is believed that carboxypeptidase E (CPE) is involved in gut hormone processing but its presence in gut endocrine cells has never been studied. We have analyzed the distribution of CPE in the antropyloric mucosa of rat stomach and report that gastrin cells and progenitor gastrin-somatostatin (G/D) cells express CPE while mature somatostatin cells and the majority of serotonin cells fail to express CPE. These data indicate that immature G/D cells are able to process gastrin to glycine-extended forms and that CPE-mediated processing is not a characteristic of mature somatostatin and serotonin cells.

Gastrin-induced gastric adenocarcinoma growth is mediated through cyclin D1

Gastrin is a gastrointestinal (GI) peptide that possesses potent trophic effects on most of the normal and neoplastic mucosa of the GI tract. Despite abundant evidence for these properties, the mechanisms governing gastrin-induced proliferation are still largely unknown. To elucidate the mechanisms by which gastrin might influence mitogenesis in gastric adenocarcinoma, we analyzed its effects on the human cell line AGS-B. Amidated gastrin (G-17), one of the major circulating forms of gastrin, induced a concentration-dependent increase in [3H]thymidine incorporation of cells in culture, with the maximum effective concentration occurring with 20 nM G-17. This effect was significantly attenuated by the gastrin-specific receptor antagonist L-365260. In addition, we found that G-17 induced a significant increase in the levels of cyclin D1 transcripts, protein, and promoter activity. The results of these studies indicate that gastrin appears to exert its mitogenic effects on gastric adenocarcinoma, at least in part, through changes in cyclin D1 expression.

Long term omeprazole therapy for reflux esophagitis: Follow-up in serum gastrin levels, EC cell hyperplasia and neoplasia

AIM: To evaluate the long-term safety of omeprazole in patients of gastroesophageal reflux disease resistant to treatment with H2 receptor antagonist.

METHODS: We prospectively followed 33 patients on omeprazole therapy for severe erosive esophagitis for 5-8 years, with periodic gastrin levels, H. pylori infection, gastric biopsies for incidence of ECL cell hyperplasia, carcinoids, gastric atrophy and neoplasia. A total 185 patient follow-up years and 137 gastric biopsies were done.

RESULTS: Among the 33 patients, 36% reached their peak gastrin levels in an average of 8 mo to one year, then drifted Down slowly over 1-2 year period to just above their baseline level, 24% of the patients had a peak gastrin level above 400 ng·L^-1 and one patient had a peak level above 1000 ng·L^-1. One patient had a mild ECL cell hyperplasia which was self-limiting and did not show any dysplastic changes. Eighteen percent of patients were positive for H. pylori infection. The gastric biopsies did not show gastric atrophy, intestinal metaplasia or neoplastic changes.

CONCLUSION: In a series of 33 patients followed for 5-8 years on omeprazole therapy for severe reflux esophagitis, we did not observe any evidence of significant ECL cell hyperplasia, gastric atrophy, intestinal metaplasia, dysplasia or neoplastic changes.

Control of c-fos expression in STC-1 cells by peptidomimetic stimuli

Enteroendocrine cells respond to nutrient and non-nutrient stimuli in the gut lumen. The intestinal hormone cholecystokinin (CCK) is secreted in response to luminal fatty acids, amino acids, peptides and proteins. The peptidomimetic cephalosporins have been reported to provide model, stable, compounds with similar secretagogue activity to peptide. Putative luminal stimuli also influence transcriptional activity in enteroendocrine cells, but the mechanisms are uncertain. In the present study we have investigated the control of c-fos expression in STC-1 cells (an enteroendocrine cell line). Peptidomimetics stimulated calcium-dependent release of CCK, and increased intracellular calcium, phosphorylation of p42/44 mitogen-activated protein kinase (MAP kinase) and c-fos mRNA abundance. Hypotonic stress also increased p42/44 MAP kinase phosphorylation and c-fos mRNA, but not CCK release. The increase in c-fos mRNA was strikingly potentiated by peptidomimetics in hypotonic medium. Increased c-fos expression, but not CCK release, was suppressed by the MAP kinase (MEK) inhibitor PD98059, and by the tyrosine kinase inhibitor genistein. We conclude that in STC-1 cells, peptidomimetics act through the p42/44 MAP kinase pathway to increase c-fos expression but not exocytosis. Moreover, a putative non-nutritive stimulus, hypotonic stress, may interact with this pathway to enhance c-fos expression, independently of hormone release.

Developmental biology of gastrin and somatostatin cells in the antropyloric mucosa of the stomach

Gastrin is a hormone regulating gastric acid secretion and the growth of the gastrointestinal epithelium. It is expressed by endocrine tumors and by adenocarcinomas of the gastroenteropancreatic region and may represent an autocrine tumor growth factor. Gastrin is also implicated in the genesis of peptic ulcer disease both in conjunction with H. pylori infections and with gastrin-producing tumors. The secretion and expression of gastrin are under the paracrine control of somatostatin, produced by D cells situated in close contact with gastrin-producing G cells. D cells also contain neuronal nitric oxide synthase and appear to regulate apoptosis of G cells by paracrine release of nitric oxide. Both G and D cells are derived from a common multihormonal precursor cell present in the regenerative (isthmus) region of the gastric units. The precursor cells have been suggested to undergo asymmetrical divisions resulting in gastrin- and somatostatin-producing daughter cells that remain in paracrine contact during their migration into the glands. The precursor cells also give rise to the third main antropyloric endocrine cell type; the serotonin-producing EC cell. The maturation of all of these cell types is regulated by a number of transcription factors containing homeobox motifs (Pdx-1, Pax 4 and 6, Isl-1, Nkx6.1). Many of these also regulate the development of the central nervous system and the pancreas. The use of different combinations of these factors for regulating the expression of different hormones may explain the phenomenon of abberant hormone expression during development and carcinogenesis and the occurrence of multihormonal cells.

Apoptosis in rat gastric antrum: evidence that regulation by food intake depends on nitric oxide synthase

The turnover of the epithelium of the gastrointestinal tract is regulated by a balance between cell multiplication and cell loss. We examined the effects of starvation on apoptosis in endocrine and other epithelial cells of rat antropyloric mucosa. Apoptosis was determined by the TUNEL reaction combined with immunocytochemical staining for gastrin and somatostatin. Apoptotic cell morphology was determined by bisbenzimide staining for DNA. Both gastrin and somatostatin cells showed a significantly lower apoptotic index than the general epithelium. This agrees with the longer turnover kinetics of gastric endocrine cells. On starvation, the apoptotic index of the general epithelium and of the gastrin but not of the somatostatin, cells increased significantly. This was prevented by the nitric oxide synthase (NOS) inhibitor L-NAME but not by its inactive stereoisomer D-NAME. Immunoreactive neuronal NOS was present in somatostatin cells, in nonendocrine cells predominating in the surface and pit epithelium, and in rare nerve fibers. Endothelial cell NOS was present in vessels, whereas the inducible isoform was barely detectable. Thus, endogenous NOS isoforms participate in regulating antropyloric epithelial apoptosis during starvation. The close paracrine relation between somatostatin cells and gastrin cells suggests that the former regulates apoptosis of the latter through release of NO.

Rapid and easy detection of Helicobacter pylori by in situ hybridization

Various in situ hybridization (ISH) methods have been used to identify Helicobacter pylori, a causative organism responsible for chronic gastritis and peptic ulcer disease, but they were hard to perform and time consuming. To detect H. pylori in a rapid and easily reproducible way, we developed synthetic biotinylated oligonucleotide probes which complement rRNA of H. pylori. Formalin-fixed and paraffin-embedded tissues from 50 gastric biopsy specimens were examined. Using a serologic test and histochemical stain (Warthin-Starry silver stain and/or Giemsa stain) as a standard, 40 of them were confirmed to be H. pylori-positive. Our ISH was quickly carried out within one hr and results were compared with those obtained from immunohistochemical stain. The ISH produced a positive reaction in 38 of 40 cases (95%). All H. pylori-negative cases failed to demonstrate a positive signal. The ISH has a sensitivity comparable to those of conventional histochemical and immunohistochemical stain, and has high specificity. In conclusion, ISH with a biotinylated oligonucleotide probe provides a useful diagnostic method for detecting H. pylori effectively in routinely processed tissue sections.

Effect of Helicobacter pylori infection on antral gastrin and somatostatin cells and on serum gastrin concentrations

OBJECTIVES

Helicobacter pylori infection induces selective reduction of the number of antral D-cells and results in abnormal regulation of serum gastrin secretion. The purpose of this study was to investigate the relationship between H. pylori infection and the numbers of G-cells and D-cells.

METHODS

The numbers of antral G-cells and D-cells, the ratio of G-cells to D-cells and fasting serum gastrin concentrations were compared between 37 patients with (29 with duodenal ulcers and 8 with gastric ulcers) and 33 without H. pylori infection (22 with duodenal ulcers and 11 with gastric ulcers). Serum gastrin concentrations were measured using the radioimmunoassay technique. Antral mucosal biopsy specimens were examined using immunohistochemical staining with antibodies specific for gastrin and somatostatin and the numbers of G-cells and D-cells per gastric gland were counted.

RESULTS

Fasting serum gastrin concentrations were significantly higher in patients with H. pylori infection compared to patients without infection (80.3 +/- 23.5 vs 47.6 +/- 14.1 pg/ml, p < 0.001). The number of G-cells per gastric gland was similar in infected and uninfected patients (7.1 +/- 3.1 vs 7.3 +/- 3.9, respectively, p > 0.5). The number of D-cells was significantly lower in patients with H. pylori infection than in uninfected patients in both duodenal and gastric ulcer patients (1.3 +/- 0.4 vs 2.5 +/- 1.6, respectively, p < 0.001). The ratio of G-cells to D-cells was also significantly higher in infected patients compared with uninfected patients for both gastric and duodenal ulcers (5.7 +/- 2.7 vs 3.5 +/- 1.9, respectively, p < 0.001).

CONCLUSIONS

These results strongly suggest that Helicobacter pylori infection induces reduction of the number of antral D-cells. The resulting relative hypofunction of the inhibitory action of D-cells against G-cells may be responsible for increased serum gastrin secretion.

Effect of omeprazole treatment on plasma concentrations of the gastric peptides, xenin, gastrin and somatostatin, and of pepsinogen

The peptide xenin 25 is a gastric mucosal constituent like gastrin, somatostatin and pepsinogen. Gastrin and pepsinogen plasma concentrations increase when the secretion of gastric acid is reduced by proton pump inhibitors. In the present investigation, treatment with omeprazole led to an increase in fasting and postprandial plasma concentrations of xenin, gastrin and pepsinogens A and C (P < 0.05, in each instance), whereas somatostatin plasma levels remained unchanged. Because subcutaneous injection of pentagastrin did not raise xenin plasma concentrations, a direct effect of gastrin on xenin production seems unlikely. This study indicates that xenin plasma concentrations are regulated by intragastric pH, as are those of gastrin and pepsinogen.

Heterogeneity of the proliferative capacity of rat cholangiocytes after bile duct ligation

We previously introduced the concept that intrahepatic bile duct epithelial cells, or cholangiocytes, are functionally heterogeneous. This concept is based on the observation that secretin receptor (SR) gene expression and secretin-induced cAMP synthesis are present in cholangiocytes derived from large (> 15 microns in diameter) but not small (< 15 microns in diameter) bile ducts. In work reported here, we tested the hypothesis that cholangiocytes are heterogeneous with regard to proliferative capacity. We assessed cholangiocyte proliferation in vivo by measurement of [3H]thymidine incorporation and in vitro by both [3H]thymidine incorporation and H3 histone gene expression in small (fraction 1) and large (fraction 2) cholangiocytes isolated from rats after bile duct ligation (BDL). In the two cholangiocyte subpopulations, we also studied basal somatostatin receptor (SSTR2) gene expression as well as the effects of somatostatin on 1) SR gene expression and secretin-induced cAMP synthesis and 2) [3H]thymidine incorporation and H3 histone gene expression. In normal rat liver, cholangiocytes, unlike hepatocytes, were mitotically dormant; after BDL, incorporation of [3H]thymidine markedly increased in cholangiocytes but not hepatocytes. When subpopulations of cholangiocytes were isolated after BDL, DNA synthesis assessed by both techniques was limited to large cholangiocytes, as was SSTR2 steady-state gene expression. In vitro, somatostatin inhibited SR gene expression and secretin-induced cAMP synthesis only in large cholangiocytes. Moreover, compared with no hormone, somatostatin inhibited DNA synthesis solely in large cholangiocytes. These results support the concept of the heterogeneity of cholangiocytes along the biliary tree, extend this concept to cholangiocyte proliferative activity, and imply that the proliferative compartment of cholangiocytes after BDL is located principally in the cholangiocytes lining large (> 15 microns) bile ducts.

Effects of calcitonin gene-related peptide on somatostatin and gastrin gene expression in rat antrum

The ability of exogenous calcitonin gene-related peptide (CGRP) to regulate gastric somatostatin and gastrin messenger RNA was studied in vitro in rat antral mucosal/submucosal tissues. Somatostatin and gastrin mRNA were quantified by Northern and dot blot hybridization and regulatory peptides were measured by radioimmunoassay. Incubation of antral tissues in the presence of CGRP [1 x 10(-7) M] for 60 min resulted in a reciprocal increase in somatostatin and a decrease in gastrin release: 214.7+/-28.5 vs. control of 81.7+/-5.9 pg somatostatin per gram of tissue and 2.2+/-0.3 vs. control of 5.5+/-0.7 ng gastrin per gram of tissue (P < 0.001). CGRP caused parallel changes in somatostatin and gastrin mRNA levels: somatostatin mRNA increased by 212% from 0.40+/-0.02 to 1.25+/-0.09 absorbance units (AU) (P < 0.001) and gastrin mRNA decreased by 73% from 0.55+/-0.08 to 0.15+/-0.02 AU (P < 0.001). Somatostatin monoclonal antibody prevented CGRP-mediated inhibition of both gastrin release and gastrin mRNA levels. In conclusion, CGRP is capable of modulating both the secretion and gene expression of regulatory peptides from antral G and D cells. Somatostatin immunoneutralization studies suggest that the actions of CGRP on gastrin release and gene expression are indirect and mediated through the paracrine influences of somatostatin.

Disturbed progastrin processing in carboxypeptidase E-deficient fat mice

The fat mouse strain exhibits a late-onset obesity syndrome associated with a mutation in the gene encoding carboxypeptidase E (CPE). Since CPE plays a central role in the biosynthesis of a number of regulatory peptides, including gastrin, we examined the biogenesis and processing of progastrin in fat/fat mice by measuring gastrin mRNA, carboxyamidated gastrin and its processing intermediates in the stomach. The tissue concentration of carboxyamidated (i.e. bioactive) gastrin was only slightly reduced (601 +/- 28 pmol/g in fat/fat mice vs. 715 +/- 43 pmol/g in wild-type controls). However, progastrin processing intermediates accumulated excessively with an 86-fold increase in the concentration of the CPE substrate, glycyl-arginine extended gastrin, and a seven-fold increase in the concentration of glycine-extended gastrin. Accordingly, the total progastrin product was doubled, as was the concentration of gastrin mRNA. Plasma concentrations of carboxyamidated gastrin were, however slightly reduced both in fasted fat/fat mice and postprandially. The results show that the CPE mutation diminishes the efficiency of progastrin processing, but gastrin synthesis is nevertheless increased to maintain an almost normal production of bioactive gastrins. By comparison with other neuroendocrine prohormones, progastrin processing in CPE-deficient mice is unique. Hence, the increase of glycine-extended gastrin in combination with normal levels of carboxyamidated gastrin suggests that G-cells may have another biosynthetic pathway for gastrin.

Interaction of nicotine and a H2-receptor antagonist, famotidine, on gastrin and chromogranin A expression

The purpose of this study is to examine the effect of nicotine on famotidine-induced hypergastrinemia in the rat. In addition, the effects of nicotine on gene expression for gastrin and chromogranin A (CGA) in the stomach were examined. Famotidine treatment alone (20 mg/kg. 2 x/day for 14 days) increased serum gastrin levels significantly (P < 0.05) but not antral levels of gastrin mRNA and peptide. Nicotine treatment (12 mg/kg/d) alone did not affect serum gastrin levels; however, nicotine potentiated the hypergastrinemic action of famotidine. The hypergastrinemic action of nicotine was not mediated by a downregulation of stomach somatostatin (SRIF) since stomach SRIF mRNA levels were unaffected by nicotine treatment. Administration of nicotine and famotidine also upregulated stomach CGA gene expression (i.e., mRNA and protein levels) significantly.

Effect of Helicobacter pylori status on intragastric pH during treatment with omeprazole

To test the hypothesis that Helicobacter pylori infection is associated with a decreased intragastric acidity during omeprazole therapy, ambulatory 24 hour dual point gastric pH recordings were performed in 18 H pylori positive and 14 H pylori negative subjects. There was a four to six week washout period between the two pH recordings made in each subject after one week courses of placebo or omeprazole, 20 mg daily. During placebo, median 24 hour pH values were not different in the corpus (H pylori positive = 1.5, negative = 1.4; p = 0.9) or antrum (H pylori positive = 1.3, negative = 1.2; p = 0.1). However, during omeprazole treatment, median 24 hour pH values were higher in H pylori positive subjects, both in the corpus (H pylori positive = 5.5, negative = 4.0; p = 0.001) and antrum (H pylori positive = 5.5, negative = 3.5; p = 0.0004). During placebo treatment, the only difference between the two groups was a higher later nocturnal pH in the antrum in the H pylori positive group. During omeprazole treatment, gastric pH was higher both in the corpus and in the antrum in the H pylori positive group for all periods, except for mealtime in the corpus. These data indicate that omeprazole produces a greater decrease in gastric acidity in subjects with H pylori infection than in those who are H pylori negative. It is not, however, known whether there is a causal relationship between H pylori infection and increased omeprazole efficacy.

Role of luminal ammonia in the development of gastropathy and hypergastrinemia in the rat

BACKGROUND/AIMS

Chronic infection with Helicobacter pylori causes persistent elevations in gastric juice ammonia levels. Thus, we studied the effects of experimentally induced increases in gastric juice ammonia levels on gastric structure and function and gastrin homeostasis.

METHODS

Rats were fed either normal chow or the diet supplemented (20 g/dL) with ammonium or sodium acetate.

RESULTS

Long-term dietary ammonium loading for 2 weeks or longer resulted in a 1.5-2-fold increase in the weight and mucosal thickness of the stomach and proximal duodenum with evidence of mild gastritis and enterochromaffinlike cell hyperplasia. The ammonium-containing diet also induced a significant 2-3-fold increase in both circulating gastrin levels of fed rats and an increase in the postprandial gastrin responses over control values. Antral gastrin levels were also markedly elevated by long-term ingestion of the test diet, which was increased 3-4-fold over control values in fasted animals and less so after meal stimulation. Consistent with these findings, gastrin-specific messenger RNA was increased 2.5-3-fold in the antrum of ammonium fed rats, whereas actin-specific messenger RNA was not affected or decreased. Animals fed a diet supplemented with 20 g/dL sodium acetate sustained modest increases in mucosal thickness and serum and antral gastrin concentration, suggesting that nonspecific gastric injury and inflammation is also a factor that influences G-cell function.

CONCLUSIONS

Long-term exposure of the antral mucosa to elevated levels of ammonia in the gastric juice in the presence of gastritis, conditions similar to that occurring in subjects infected with H. pylori, seem to be causative factors in the development of G-cell hyperfunction.

Effects of hypochlorhydria and hypergastrinemia on structure and function of gastrointestinal cells. A review and analysis

Since hypochlorhydria can induce hypergastrinemia, and gastrin has a trophic effect on some gastrointestinal cells, states that cause elevated plasma gastrin levels are of interest in terms of effects on cell growth and function. This article reviews the relationship between gastric mucosal cells during periods of acid stimulation and inhibition and analyses the effects of hypochlorhydria and hypergastrinemia on gastric and colonic cells and tumors. Hypochlorhydria releases the inhibitory effect of antral gastrin cells, inducing them to release gastrin in the presence of peptides or amino acids in the gastric lumen or in response to antral distension. Gastrin stimulates the oxyntic mucosa, which may lead to hyperplasia of enterochromaffin-like cells, resulting in enterochromaffin-like carcinoid tumors in aged rats and, rarely, in patients with chronic atrophic gastritis or gastrinomas. In addition to hypergastrinemia, other factors appear to be required for the progression of enterochromaffin-like hyperplasia to carcinoids; genetic factors may be involved. Gastrin elevations due to antisecretory drug therapy are indirectly proportional to the degree of acid inhibition and are reversible upon cessation of therapy. The gastrin levels during omeprazole therapy are similar to those caused by gastric vagotomy. Available evidence does not support a relationship between hypergastrinemia and the occurrence or growth of gastric carcinoma or colonic tumors.

A randomised trial of octreotide vs best supportive care only in advanced gastrointestinal cancer patients refractory to chemotherapy

Octreotide, a somatostatin analogue, has been shown to inhibit the growth of gastrointestinal cancers in vitro and in vivo. To assess the anti-tumour effect of octreotide, we performed a randomised trial comparing octreotide with best supportive care in advanced gastrointestinal cancer patients refractory to chemotherapy. A total of 107 patients with advanced gastrointestinal cancer refractory to chemotherapy were randomised to receive octreotide at the dose of 200 micrograms three times a day for 5 days a week, or the best supportive care only. The primary outcome variable was the survival duration. Response rate was an outcome variable of secondary importance. Fifty-five patients (15 stomach, 16 pancreas, 24 colon-rectum) received octreotide, while 52 (14 stomach, 16 pancreas, 22 colon-rectum) received the best supportive care. Patients treated with octreotide had a significant advantage in duration of survival with a median survival time of 20 weeks vs 11 in the control group (P < 0.0001). This advantage was present also considering the survival data for each tumour group. Twenty-five patients (45%) given octreotide showed stable disease vs only eight (15%) in the control group (P < 0.001). In conclusion, octreotide therapy seems to confer a survival benefit in advanced gastrointestinal cancer patients refractory to chemotherapy. Additional studies will be needed to confirm these results and to clarify other questions about dose and schedule of octreotide.

Effects of carbamylcholine chloride on human antral gastrin mRNA levels

The effects of the muscarinic receptor agonist, carbamylcholine chloride (carbachol), on gastrin release and gastrin mRNA levels in human antral mucosa (n = 15) were determined. During a-2-h incubation period, carbachol (10(-6)-10(-4) M) decreased gastrin mRNA levels to 71 +/- 8% (10(-6) M), 40 +/- 8% (10(-5) M), and 33 +/- 5% (10(-4) M) of control levels. Carbachol (10(-5) M) decreased intracellular gastrin (from 1634 +/- 103 to 1272 +/- 126 pg/mg tissue protein), while it increased gastrin release into the medium (from 609 +/- 48 to 918 +/- 68 pg/ml per mg tissue protein). After 6- and 9-h culture, carbachol gradually increased gastrin mRNA levels, by 96 +/- 12% and 126 +/- 23%, respectively. Atropine sulfate (10(-5) M) completely inhibited the carbachol-induced changes. Cycloheximide markedly decreased tissue gastrin concentration, but increased gastrin mRNA levels, whereas it had no effects on gastrin release. These findings suggested that carbachol may have a time-related biphasic action on human antral gastrin biosynthesis.

Detection of gastrin mRNA in paraffin-embedded samples of normal antral mucosae using polymerase chain reaction technique

Gastrin, a peptide hormone produced by the G cells of the gastric antrum, plays a major role in the regulation of digestive mucosal growth. Although some light has been shed on the peptidic aspects of this hormone's mode of action and the co-regulatory activity in which it is involved along with the other gastrointestinal hormones, little is known at present about the modes of expression of its mRNA at the tissue level. A few attempts have been made so far to detect the transcript, mostly using molecular hybridization techniques. Here it was proposed to detect gastrin mRNA using a RT-PCR technique on a series of paraffin-embedded samples of normal human antrum processed with various fixatives commonly used in histology. The transcript was detectable in all the 7-microns sections of the samples treated with either formalin or Carnoy's solution, whereas Bouin's solution, which is also used as a fixative in histology, was found to have inhibitory effects on the method described here.

Reciprocal changes in antral gastrin and somatostatin mRNA in pernicious anemia

Somatostatin is involved in the regulation of gastrin by intragastric pH in animal models. To investigate whether this is so in man, we measured gastrin and somatostatin mRNA in endoscopic biopsies from six patients with hypergastrinemia and achlorhydria due to pernicious anemia and 12 age- and sex-matched controls. The pernicious anemia patients had significantly higher fasting plasma gastrin concentrations with a median (range) of 640 (420-3500) pmol/liter compared with 5 (2-58) pmol/liter, P < 0.001. The median gastrin mRNA/rRNA ratio was 10.4 (3.7-38.0) in the pernicious anemia patients compared with 1.7 (0.7-8.3) in the controls (P < 0.02), and it correlated strongly with the plasma gastrin concentration, r = 0.93, P < 0.0001. In contrast, the median somatostatin mRNA/rRNA ratio was lower in the pernicious anemia patients 0.84 (0.58-2.32) versus 2.04 (0.05-6.47) in the controls, P < 0.05. These findings suggest that in pernicious anemia gastric neutralization leads to hypergastrinemia through the modulation of antral gastrin synthesis by somatostatin.

Evolution of the gastrointestinal endocrine system (with special reference to gastrin and CCK)

The evolution of gut endocrine cells can be seen to have depended in the first instance on the expression of genes encoding regulatory peptides in cells that had evolved the regulated pathway of secretion. It seems probable that the endocrine cells made use of molecules and mechanisms that first emerged in early nervous systems. However, by the start of the vertebrate line of evolution, most of the major families of gut hormones were already found in association with endocrine cells. A single common class of receptor with seven transmembrane domains and acting via association with G-proteins transduces many (perhaps all) gut peptide actions. The duplication and divergence of receptors and peptides can now be traced, in outline at least, for gastrin and CCK in vertebrates. Even in phylogenetically similar groups such as birds and mammals, quite different molecular approaches have been applied to solving the same physiological problem. Evolution of the modern gastrointestinal control system evidently depended in this case both on molecular evolution of peptides and receptors and on cells expressing the genes encoding them.

Somatostatin: physiology and clinical applications

Somatostatin (SOM) was originally isolated as the hypothalamic inhibitor of growth hormone release but was subsequently shown to have a widespread distribution including the gastrointestinal tract. In fact the gastrointestinal tract contains about 70% of the total body SOM. SOM has inhibitory actions on gastrointestinal exocrine and endocrine secretions, motility and blood flow. Within the gut it functions as an endocrine, paracrine, autocrine and neurocrine factor. SOM is released by a meal, and a number of neurotransmitters and regulatory peptides also influence SOM release. SOM is a key component of the gastrin-acid feedback loop as luminal acid releases SOM, which in turn has inhibitory effects on both gastrin and gastric acid. Consistent with the diverse functions of SOM, a number of different although related SOM receptors with distinct distribution patterns and intracellular mediators have been cloned and sequenced. SOM is the first of the gut regulatory peptides to have a significant therapeutic use. By inhibiting both the target cell (e.g. parietal cell) and the release of the active agent (e.g. gastrin) the therapeutic potential of SOM is magnified. To date most of the clinical experience has been with the one analogue, octreotide. This analogue has a longer half-life than SOM (hours versus minutes) but has only minimal oral activity, therefore requiring subcutaneous injections several times a day. The definite gastrointestinal applications include treatment of gastroenteropancreatic tumours. It is also becoming a favoured treatment for gastrointestinal fistulae, variceal bleeding and diarrhoea. However, octreotide has no consistent effect on tumour growth. The high density of SOM receptors on tumours has allowed localization of tumours using in vivo scintography with labelled octreotide. The sequencing of a variety of SOM receptors with different distributions and differing cellular effector systems raises the likelihood of developing SOM analogues for specific clinical applications.

Inhibitory effects of antagonists of bombesin/gastrin releasing peptide (GRP) and somatostatin analog (RC-160) on growth of HT-29 human colon cancers in nude mice

Nude mice bearing xenografts of HT-29 human colon cancer cell line were treated for 4 weeks with somatostatin analog (RC-160), bombesin/gastrin releasing peptide (GRP) antagonists (RC-3095 and RC-3440). In three separate experiments somatostatin analog RC-160 (50 micrograms/day) released from microgranules significantly reduced tumor growth. Bombesin/GRP antagonists, RC-3095 and RC-3440 injected subcutaneously (s.c.) twice daily at a dose of 10 micrograms had the greatest and consistently significant inhibitory effect on tumor growth. RC-3095 given once daily s.c. at a dose of 20 micrograms was less effective. RC-3095 also inhibited metastatic tumor growth after intrasplenic injection of HT-29 cells in nude mice. Specific binding sites of somatostatin, bombesin and epidermal growth factor (EGF) were detected on intact HT-29 cells or on the membranes from HT-29 tumor xenografts. The inhibitory effects of bombesin antagonists on tumor growth were consistently linked with a significant down-regulation of EGF receptors. Bombesin/GRP antagonists and somatostatin analogs could be considered for the development of new hormonal therapies for colon cancer.

Effect of Helicobacter pylori eradication on antral gastrin- and somatostatin-immunoreactive cell density and gastrin and somatostatin concentrations

The density of antral gastrin (G)- and somatostatin (D)-immunoreactive cells and the contents of antral gastrin and somatostatin were investigated in endoscopic antral biopsy specimens from patients with duodenal ulcer before and after eradication of Helicobacter pylori. After H. pylori eradication both antral somatostatin concentration (p = 0.0002) and antral D-cell density (p = 0.01) increased significantly. Conversely, although the number of G-cells was unchanged, antral (p = 0.0002) and serum (p = 0.001) gastrin contents decreased significantly. The number of oxyntic D-cells did not change significantly. These results strongly suggest that the hypergastrinaemia observed in H. pylori-positive patients may be due to a deficiency in antral somatostatin, which normally inhibits the synthesis and release of gastrin.

Inhibition of omeprazole induced hypergastrinaemia by SMS 201-995, a long acting somatostatin analogue in man

Whether the long acting somatostatin analogue SMS 201-995 (octreotide, Sandostatin) could inhibit the basal and meal stimulated hypergastrinaemia and hyperpepsinogenaemia induced by omeprazole was investigated. Eight healthy subjects were randomised to receive five day courses of SMS 201-995 (25 micrograms subcutaneously three times daily), omeprazole (40 mg once a day), a combination of both drugs, or placebo. Basal and meal stimulated serum gastrin and basal serum pepsinogen A and C values were measured the day before treatment, on day five of treatment, and the day after each course of treatment. Omeprazole caused significant increases in basal and meal stimulated peak and integrated serum gastrin values and pepsinogen A and C levels, which were still significantly raised the day after stopping omeprazole treatment. Giving SMS 201-995 with omeprazole significantly reduced any omeprazole induced increases in basal and meal stimulated peak and integrated serum gastrin levels; serum pepsinogen A and C values were significantly inhibited too. Serum gastrin values during combined therapy were not significantly different from those during placebo treatment, whereas pepsinogen A and C levels were still significantly raised. On the day after stopping combined therapy, basal and meal stimulated peak and integrated serum gastrin and serum pepsinogen C (but not pepsinogen A) levels were not significantly different from values obtained on the day after stopping omeprazole alone. SMS 201-995 without omeprazole significantly inhibited basal and meal stimulated peak and integrated serum gastrin levels. Pepsinogen A was also significantly inhibited by SMS 210-995, but the reduction in pepsinogen C failed to reach statistical significance. In conclusion, SMS 201-995 prevents basal and meal stimulated increases in serum gastrin during omeprazole therapy. This finding may have clinical importance in the few patients who have pronounced hypergastrinaemia because of profound long acting acid inhibition.

Evidence for the effect of aging on tissue contents of gastrin, cholecystokinin and somatostatin in the rat

The changes associated with aging in the tissue concentrations of cholecystokinin, somatostatin and gastrin in young (7-month-old), middle-aged (13-month-old) and old (25-26-month-old) rats were investigated. The concentrations and total contents of somatostatin and gastrin significantly decreased in the antrum in 13- and 25-26-month-old rats compared with the young controls. The cholecystokinin concentration in the proximal intestine and its total content significantly increased in the old rats. Somatostatin concentrations in the intestine and cerebral cortex did not change with age. Cholecystokinin content in the cerebral cortex decreased in old rats because of the decrease of tissue wet weight. We conclude that the effects of aging on the changes of peptide concentrations in tissues vary depending on peptide specie and in different tissues studied.

Achlorhydria induced changes in gastrin, somatostatin, H+/K+-ATPase and carbonic anhydrase in the sheep

Gastrin, somatostatin, H+/K(+)-ATPase and carbonic anhydrase are principal elements of acid secretion. We investigated in the conscious sheep the effect of 24 h omeprazole (an H+/K(+)-ATPase inhibitor) infusion on these elements at the level of synthesis, storage and secretion. Omeprazole inhibited acid secretion-pH increased from 3.0 to 7.1 at 24 h. Plasma amidated and glycine extended gastrin increased 3-fold while the ratio of amidated to glycine extended gastrins (4:1) remained unchanged. Despite the increase in circulating gastrin, antral gastrin concentration and mRNA did not change significantly. Gastrin-17 (amidated and glycine extended) was the predominant form in the circulation and antrum, although there were preferential increases in larger forms following omeprazole treatment. Omeprazole had no effect on somatostatin mRNA or peptide levels in the fundus. Similarly, plasma somatostatin remained unchanged. However, antral somatostatin increased significantly (63%) following omeprazole treatment accompanied by a 4-fold increase in its mRNA. Fundic H+/K(+)-ATPase mRNA was unchanged but a significant increase (87%) in carbonic anhydrase II mRNA was observed. Omeprazole induced hypergastrinaemia occurred without a measurable reduction in storage or increased synthesis of gastrin at 24 h. Increased antral somatostatin synthesis and storage may result from stimulation by plasma gastrin on antral D cells, independent of acid. The rise in carbonic anhydrase II mRNA in the absence of any change in H+/K(+)-ATPase mRNA may reflect the differential sensitivity of the genes encoding these two enzymes to the stimulatory action of gastrin.

Somatostatin inhibition of gastrin gene expression: involvement of pertussis toxin-sensitive and -insensitive pathways

These studies were performed to determine the intracellular pathways involved in regulating gastrin gene expression. The inclusion of 10(-4) M forskolin or 10(-4) M dibutyryl cyclic AMP (DBcAMP) in incubation medium containing dog antral mucosa resulted in 249% and 323% increases, respectively, in gastrin mRNA levels. The stimulatory effects of forskolin and DBcAMP were both inhibited significantly by 10(-6) M somatostatin. Preincubation of antral mucosa with pertussis toxin nearly abolished the inhibitory effects of somatostatin on gastrin mRNA stimulated by forskolin, but had no effect following DBcAMP. To examine whether calcium-dependent pathways might be involved in regulating gastrin gene expression, antral mucosa was incubated with increasing concentrations of calcium or the ionophore ionomycin. Both agents produced only modest increases in gastrin mRNA, which were abolished by the addition of somatostatin to the incubation medium. These studies indicate that somatostatin appears to inhibit gastrin gene expression through mechanisms involving both pertussis toxin-sensitive and -insensitive pathways.

The effects of peptide histidine isoleucine on antral gastrin and somatostatin

The present studies were directed to determine whether peptide histidine isoleucine (PHI) affects expression of the gastrin and somatostatin genes and whether such effects may be functionally linked. In separate experiments, the effects of PHI on medium gastrin and somatostatin concentrations, the incorporation of 35S-labelled amino acids into newly synthesized gastrin and somatostatin, and steady state gastrin and somatostatin mRNA were determined. PHI inhibited basal expression of the gastrin gene at all levels examined, while no significant effect on basal somatostatin gene expression could be detected. PHI also decreased carbachol-stimulated antral gastrin release and simultaneously increased somatostatin release. However, in contrast to its structural analogues, secretin and gastric inhibitory peptide, the immunoneutralization of endogenous somatostatin by the administration of specific antibodies did not affect significantly the capacity of PHI to inhibit gastrin release into the culture medium stimulated by carbachol. The results of these studies indicate that PHI exerts a physiological inhibitory effect on antral gastrin cells and that this inhibition may occur at several steps along the biosynthetic pathway. In addition, unlike its structural analogues, PHI inhibition of carbachol-stimulated gastrin release is not functionally linked to its stimulatory effects on somatostatin release.

Regulation of rat antral gastrin and somatostatin gene expression during starvation and after refeeding

Antral gastrin and somatostatin gene expression during starvation and after refeeding with liquid meals of varying composition were studied. Northern and slot-blot hybridization analyses showed that starvation caused a marked decrease in antral gastrin messenger RNA (mRNA) level by 12 hours associated with an increase in somatostatin mRNA. After 48 hours of fasting, antral gastrin mRNA was 26% and somatostatin mRNA was 136% of their prefasting levels. Refeeding caused increased 2-hour integrated gastrin mRNA levels after liquid peptone (+45%), phenylalanine (+31%), and olive oil (+13%), but no changes were observed with glucose or saline solutions. Integrated 2-hour immunoreactive antral gastrin content was increased after peptone (+106%), phenylalanine (+68%), and olive oil (+32%) meals but was not increased after glucose (-11%) or saline (-10%). In some cases, both gastrin mRNA and peptide responses could be measured as early as 15 minutes. The same nutrients that increased gastrin mRNA levels caused decreased 2-hour integrated somatostatin mRNA levels; peptone (-30%), phenylalanine (-28%), and olive oil (-21%), but neither glucose nor saline, altered somatostatin mRNA levels. These results suggest that antral gastrin and somatostatin genes were regulated in opposite directions, in a coordinate manner, by specific gastric nutrients that stimulate gastrin release.

Influence of food deprivation on intestinal cholecystokinin and somatostatin

Dietary stimulation has trophic effects on the gastrointestinal tract, whereas prolonged fasting causes mucosal atrophy. Whether gastrointestinal endocrine cells within the mucosa are similarly affected is unknown. The present study was designed to determine the effects of food deprivation and refeeding on cholecystokinin (CCK) and somatostatin in the rat small intestine. RNA was prepared from the duodenum, and peptide and messenger RNA (mRNA) levels of CCK, somatostatin, and beta-actin were analyzed by hybridization with complementary DNA probes. During food deprivation for up to 5 days, plasma CCK levels decreased rapidly, followed by a decline in duodenal CCK mRNA levels and a more gradual decrease in mucosal CCK peptide concentrations. After 3 days of fasting, one group of rats was refed. After only 1 day of refeeding, all parameters (levels of plasma CCK, duodenal CCK mRNA, and duodenal CCK peptide) were restored to control levels. The reduction in CCK mRNA levels seen with fasting was specific, because food deprivation and refeeding produced no changes in either duodenal somatostatin concentrations or mRNA levels of somatostatin and beta-actin. These findings provide initial evidence that food deprivation inhibits duodenal CCK mRNA levels but does not affect duodenal somatostatin.

Reversal by omeprazole of the depression of gastrin cell function by fasting in the rat

1. Gastrin (G)-cell function is controlled by gastric acid, which has inhibitory effects, and food in the gastric lumen, which has stimulatory effects. We have examined the role of acid in mediating the depression of G-cell function that occurs in fasting in the rat. 2. Rats were fasted for 48 h, and received either the H(+)-K(+)-ATPase inhibitor omeprazole, to reduce acid secretion, or vehicle. Basal acid secretion was not significantly different after fasting for 24 or 48 h. Fasted rats which received omeprazole were achlorhydric. 3. In rats treated with vehicle and fasted for 48 h, plasma and tissue gastrin concentrations were significantly depressed. The fall in both parameters suggests an inhibition of gastrin synthesis and consistent with this a decrease was observed in tissue gastrin mRNA abundance and in phosphorylation of progastrin-derived peptides. 4. In fasted rats treated with omeprazole, tissue gastrin concentrations were not significantly different from those of rats fed ad libitum, but plasma gastrin concentrations were significantly higher than in rats fed ad libitum. Gastrin mRNA abundance and the phosphorylation of progastrin-derived peptides in omeprazole-treated rats was not significantly different from rats fed ad libitum. 5. The data suggest that the depression of G-cell function which occurs in fasted rats can be attributed to the inhibitory action of intraluminal acid on the G-cell. Gastric acid appears to regulate several different aspects of G-cell function, including gastrin synthesis, post-translational processing and secretion.

Cysteamine induces cholecystokinin release from the duodenum. Evidence for somatostatin as an inhibitory paracrine regulator of cholecystokinin secretion in the rat

To determine whether cholecystokinin secretion is regulated by endogenous somatostatin, somatostatin deficiency was induced in vivo with cysteamine (250 mg/kg body wt, IV) or anti-somatostatin antiserum in anaesthetized rats and in vitro with cysteamine (30 micrograms/mL) in a rat duodenum-incubation system. Cholecystokinin secretion was assessed in vivo by measuring amylase in duodenal perfusates collected at 10-minute intervals for 1 hour and in vitro by a carboxy-terminal radioimmunoassay. Cysteamine induced a marked decrease in duodenal immunoreactive somatostatin both in vivo (50%) and in vitro (60%). The rate of amylase secretion increased from 9.7 +/- 2.1 U (mean +/- SE) to 28.0 +/- 4.8 U at 20 minutes (P less than 0.001). The cholecystokinin-receptor antagonist CR-1392 abolished amylase response for 30 minutes, whereas the more potent antagonists Asperlicin (18.0 mg/kg body wt, IV) and L-364,718 (0.25 mg/kg body wt, IV) caused prolonged blockade. The rate of amylase secretion in gastrectomized animals increased from 7.2 +/- 2.0 U to 15.0 +/- 2.2 U 20 minutes after cysteamine administration (P less than 0.01), indicating that the effect was not due to the presence of gastrin. In vitro, cysteamine caused a nearly fourfold increase in cholecystokinin secretion compared with controls (63.1 +/- 4.9 vs. 15.2 +/- 3.7, respectively; P less than 0.001). In vivo immunoneutralization of circulating somatostatin with a high-affinity and high-capacity antiserum produced no significant change in the rate of amylase secretion. These results suggest that cholecystokinin secretion is tonically inhibited by somatostatin and that this effect is mediated by locally secreted (paracrine) but not by circulating somatostatin.

Effects of dietary protein alterations on circadian rhythms of gastrointestinal peptides in rats

Altered protein diets and circadian rhythms of gastrin and cholecystokinin (CCK) were investigated in 126 male and 126 female Sprague-Dawley rats acclimated for two weeks to a 12:12 hr light-dark cycle. Rats were divided equally and fed low-protein (8%), high-protein (64%) or normal protein (27%) diets for four weeks. All animals were fasted for 24 hr prior to blood collections. Blood samples were collected at 4-hr intervals for 24 hr for determination of plasma gastrin and CCK using specific radioimmunoassays. A significant rhythm for gastrin was detected in males on normal and low-protein diets (P less than 0.03) and in females on low-protein diets (P less than .02). A significant rhythm for CCK was detected (P less than 0.05) in rats of both sexes fed normal and high-protein diets. Mean plasma levels of both peptides were lower in females than males. In a separate study, food intake and body weight were monitored in male rats receiving the three diets over 21 days. Animals on the low-protein diet exhibited reduced food intake and body weight compared to rats fed the normal or high-protein diets.

Studies of regulation of gastrin synthesis and post-translational processing by molecular biology approaches

We have examined the regulation of gene expression and post-translational processing of progastrin by starvation and feeding in rats. An oligonucleotide complementary to rat preprogastrin cDNA was used in RNA blot and hybridization analysis to measure gastrin mRNA levels. A region-specific antibody raised against the predicted amino acid sequence of the carboxyl terminal extension of progastrin was used for quantitation of progastrin peptides. The effects of starvation and of refeeding on rat antral gastrin mRNA and pro-hormone peptide levels were examined in rats starved for 48 h and after refeeding with a solid meal. Antral gastrin mRNA concentrations decreased to a plateau level (30% of the nonstarved control) after 48 h of starvation. Immunoreactive gastrin concentration decreased threefold, but progastrin processing intermediates did not decrease significantly during fasting. Following refeeding, significant increases in antral mRNA level were detected in 1 h, and peak levels were reached by 2 h (more than two times higher than starved control). There was a rapid and significant decrease in progastrin immunoreactivity within 30 min, followed by a significant increase in gastrin immunoreactivity 2 h after refeeding. These data suggest that rapid increases of blood and tissue gastrin levels in response to food may be associated with increases in both gastrin gene expression and post-translational processing of progastrin.

A monoclonal antibody to somatostatin with potent in vivo immunoneutralizing activity

The spleen from a Robertsonian mouse with high titer and affinity antiserum after being immunized with somatostatin-14 conjugated to keyhole limpet hemocyanin was fused with FOX-NY cells. Hybridomas were cloned by limiting dilution, subcloned, and ascites was produced from the highest affinity close in pristine-primed Balb/c mice. Ascites fluid contained approximately 20 mg/ml IgG and bound 50% of 1 fmol 125I-[Tyr1]-somatostatin at a final dilution of 1:10,000,000. Binding of this IgG1 antibody, CURE.S6, was inhibited by 50% at 40 pM concentrations of either somatostatin-14 or somatostatin-28, but was not inhibited by [D-Trp8 -somatostatin at 1000-fold higher concentrations. The antibody produced very intense specific immunohistochemical staining of somatostatin endocrine cells in the stomach and pancreas and of intestinal somatostatin neurons with extremely low background staining. Intravenous injection of 2 mg purified antibody in urethane-anesthetized rats resulted in 300-fold increase in plasma GH within 15 min. CURE.S6 is a high affinity monoclonal antibody directed at the biologically active somatostatin ring structure. This antibody is useful for in vivo immunoneutralization of exogenous and endogenous somatostatin in the rat and also is an excellent reagent for immunohistochemical localization of somatostatin.