Identity and regulation of stored and secreted progastrin-derived peptides in sheep

Amidated and nonamidated progastrin-derived peptides have distinct biological activities that are mediated by a range of receptor subtypes. The objective was to determine the nature of the stored and secreted progastrin-derived peptides and to investigate whether progastrin release is regulated by gastric acidity. Using an antiserum directed to the C terminus of progastrin for identification and to monitor purification, C-terminal flanking peptides (CTFP) of progastrin (prog(76-83), prog(77-83), and prog(78-83) in approximately equivalent amounts) were isolated and identified from extracts of sheep antrum using ion exchange, HPLC, and mass spectrometry. Only trace amounts of full-length progastrin were present. Progastrin CTFP was the predominant progastrin-derived peptide in the antrum [progastrin CTFP/gastrin amide (Gamide) = 3]. Similarly, progastrin CTFP was the major circulating form in the antral (CTFP, 710 +/- 62 pmol/liter; Gamide, 211 +/- 35 pmol/liter) and jugular (CTFP, 308 +/- 16 pmol/liter; gastrin amide, 32 +/- 3 pmol/liter) veins. Alteration of gastric acidity in sheep by iv infusion of a H/K-adenosine triphosphatase inhibitor or somatostatin or by intragastric infusion of HCl demonstrated that the CTFP concentrations changed, although to a lesser extent than the changes in circulating gastrin amide. We conclude that the CTFP of progastrin is the major stored and circulating species of the gastrin gene, and that it is secreted in a regulated fashion rather than constitutively. Because full-length progastrin is bioactive, but is only a minor antral and secreted form, determination of the biological activity of the C-terminal flanking peptides will be important for a complete understanding of gastrin endocrinology.     

Expression of Progastrin-Derived Peptides and Somatostatin in Fundus and Antrum of Nonulcer Dyspepsia Subjects With and Without Helicobacter pylori Infection

The hypergastrinemia and hyperacidity associated with Helicobacter pylori infection has been explained by either a primary excess of gastrin or a lack of inhibitory influence by somatostatin (SOM). The objective of the present study was to compare the concentrations of fundic and antral SOM- and antral progastrin-derived peptides in nonulcer dyspepsia (NUD) subjects with and without H. pylori infection. Antral and fundic mucosal biopsies were extracted and assayed for SOM and gastrin amide, glycine–extended gastrin (gastrin gly), progastrin, and total gastrin. There was a significant sixfold reduction in antral SOM but no change in fundic SOM content in H. pylori-infected subjects compared to uninfected subjects. Antral gastrin amide concentrations were significantly higher in infected subjects. However, the concentrations of the nonamidated gastrin forms (progastrin and glycine-extended gastrin) were significantly lower in the infected subjects, indicating an increased conversion of the precursor forms of gastrin to amidated gastrin, the type known to stimulate gastric acidity. The present study demonstrates that the elevated gastrin concentrations associated with H. pylori infection may be due to a reduction in the paracrine inhibitory effect of SOM on antral gastrin release. In addition, the posttranslational processing of gastrin to the amidated forms is increased in infected subjects, explaining why the elevation in antral gastrin is confined to the amidated form.     

Effects of Cyclooxygenase-2 Inhibition on Serum and Tumor Gastrins and Expression of Apoptosis-Related Proteins in Colorectal Cancer

The objective of the present study was to determine the influence of cyclooxygenase-2 (COX-2) inhibition by Celecoxib (CLX) in humans with distal colorectal adenocarcinoma (CRC) on serum and tumor levels of progastrin and gastrin and serum levels of proinflammatory cytokines (IL-8, TNF-α). In addition, the effects of this CLX treatment on tumor and adjacent mucosa expression of gastrin, its receptors (CCK₂), and COX-1 and COX-2, as well as protein expression of the active form of nuclear factor κ B (NFκ B) and the apoptotic-related proteins Bcl-2 and survivin, have been examined. Ten distal CRC patients were examined twice, once before and then after 14-day treatment with CLX (200 mg bid). Large biopsy samples were taken from the tumor and intact mucosa 10 cm above the tumor. For comparison, 20 age- and sex-matched healthy controls were enrolled and treated with CLX as CRC patients. Serum levels of IL-8 and TNF-α were measured by enzyme-linked immunosorbent assay, and serum levels of amidated gastrins and progastrin, by specific radioimmunoassay. The gene or protein expressions of progastrin, gastrin, CCK₂, COX-1, COX-2, Bcl-2, and survivin as well as NFκ B were determined by RT-PCR or Western blot in biopsy samples of tumor and intact mucosa of CRC patients. Serum IL-8 and TNF-α values were severalfold higher in CRC patients than in controls. The increase in serum proinflammatory cytokines was accompanied by increased expression of the active form of NFκ B. Serum progastrin levels were also found to be significantly higher in CRC than in controls. Treatment of CRC with CLX resulted in a significant decrease in serum levels of progastrin and this was accompanied by an increment in tumor expression of COX-2 with a concomitant reduction in gastrin, Bcl-2, survivin, and NFκ B expression. We conclude that (1) distal CRC patients show significantly higher serum progastrin levels than matched healthy controls, confirming that this hormone may be implicated in rectal carcinogenesis; (2) CRC patients exhibit significantly higher serum levels of IL-8 and TNF-α than healthy controls, probably reflecting more widespread inflammatory reaction in the colonic mucosa in CRC; (3) gastrin, COX-2, Bcl-2, survivin, and NFκ B were overexpressed in CRC tumor compared to intact mucosa, but treatment with CLX significantly reduced serum levels of progastrin and IL-8 and TNF-α, which could mediate the up-regulation of COX-2 in CRC; and (4) CLX also enhanced expression of COX-2, while inhibiting the expression of gastrin, Bcl-2, survivin, and NFκ B, suggesting that COX-2 inhibition might be useful in chemoprevention against CRC, possibly due to suppression of the antiapoptotic proteins and reduction in progastrin-induced and NFκ B-promoted tumor growth.     

Progastrin and cyclooxygenase-2 in colorectal cancer

Colorectal cancers (CRCs) are one of the most common forms of cancer in Poland and one of the leading causes of death. The tumors have been attributed to genetic, dietary, and other environmental factors, but recently growth factors such as gastrin have also been implicated in the carcinogenesis. The relationship between plasma amidated and nonamidated gastrin in CRCs is controversial. This study was designed (1) to determine the plasma levels of progastrin and amidated gastrin in 50 CRC patients before and 3–6 months after removal of the tumor, (2) to determine the tumor concentrations of these gastrin peptides and the level of expression for gastrin mRNA and gastrin/CCK_B receptor mRNA, (3) to examine the expression of cyclooxygenase COX-1 and COX-2 mRNA in CRC tissue, and (4) to compare the prevalence of Hp and its cytotoxic protein, CagA, and cytokines (TNF, IL-1, and IL-8) in CRCs, before and after removal of tumor. It was found that the CRC, its resection margin, and the plasma contained severalfold higher levels of progastrin than of amidated gastrins and that the removal of the CRC tumor resulted in a marked reduction in plasma progastrin level without a significant alteration in plasma levels of amidated gastrins. Both gastrin and CCK_B-R mRNA were detected in the cancer tissue and resection margin by RT-PCR, and similarly, COX-1 and COX-2 mRNA were expressed in these tissues of most CRCs. The seroprevalence of Hp, especially that expressing CagA, and levels of IL-1, but not other cytokines, were significantly higher in CRC patients than in 100 age-, gender-, and profession-matched controls and did not change significantly about 3–6 months after tumor resection. We conclude that (1) the CRC and its margin contain large amounts of progastrin and show gene expression of gastrin, CCK_B-R, and COX-2; (2) removal of the CRC markedly reduces the plasma concentrations of progastrin; (3) the Hp infection rate is higher in CRC, and this may contribute to colorectal cancerogenesis via enhancement of progastrin and gastrin release; and (4) plasma progastrin concentrations might serve as a biomarker of CRC.     

Expression of progastrin-derived peptides and gastrin receptors in a panel of gastrointestinal carcinoma cell lines

To assess the potential of gastrin receptor antagonists in the treatment of gastrointestinal cancer, the presence of an autocrine loop involving progastrin-derived peptides has been investigated in two colorectal and one gastric carcinoma cell lines. Progastrin, glycine-extended gastrin and amidated gastrin were detected in cell extracts or conditioned media by radio-immunoassay. Low-affinity binding sites for glycine-extended gastrin and amidated gastrin were present, but high-affinity binding sites were not detected with the appropriate iodinated ligands. In addition, neither glycine-extended gastrin nor amidated gastrin in the concentration range 10pmol/L-10nmol/L stimulated cell proliferation. We conclude that it is unlikely that the carcinoma cell lines LIM 1215, LIM 1839 and LIM 1899 use either amidated or glycine-extended gastrins as extracellular autocrine growth factors.     

Progastrin processing during antral G-cell hypersecretion in humans

Using radioimmunoassays specific for essential processing sites of human progastrin in combination with chromatography before and after cleavage with trypsin and carboxypeptidase B, we have examined antral biopsy specimens and serum from 10 hypergastrinemic patients with fundic atrophic gastritis and 7 normal control subjects. Four types of processing were studied: N-terminal proteolysis (at the N-terminus of component I, gastrin 34, and gastrin 17); C-terminal proteolysis (at the C-terminus of the amide donor, glycine93 in preprogastrin); alpha-carboxyamidation (of phenylalanine92); and O-sulfation (of tyrosine87). The results show that progastrin during permanent G-cell hypersecretion is less completely processed with respect to C-terminal proteolysis, alpha-amidation, and tyrosine-sulfation. In contrast, the degree of N-terminal proteolysis is normal. Thus, the processing of progastrin adjacent to the active site of gastrin is more restrictively controlled than N-terminal processing during G-cell hypersecretion associated with pernicious anemia.     

The role of gastrin and cholecystokinin in normal and neoplastic gastrointestinal growth

Abstract Gastrin and cholecystokinin (CCK) act as growth factors for the gastric mucosa and the pancreas, respectively. CCK is also responsible, via the CCK-A receptor, for the pancreatic hyperplasia observed following the feeding of protease inhibitors or pancreaticobiliary diversion. Hypergastrinaemia does not increase the incidence of spontaneous gastrointestinal carcinoma, but does stimulate the proliferation of gastric enterochromaffin-like cells via the gastrin/CCK-B receptor, with a consequent increase in the incidence of gastric carcinoids. Whether gastrin influences mutagen-induced gastrointestinal carcinogenesis is still controversial, but CCK clearly enhances the induction by carcinogens of acinar tumours in the pancreas. While gastrin increases xenograft growth of 50% of gastrointestinal tumours tested, effects on the proliferation of gastrointestinal tumour cell lines in vitro have been more difficult to demonstrate, perhaps because many cell lines are already maximally stimulated by autocrine gastrin. Gastrin mRNA and progastrin, but not mature amidated gastrin, have been detected in all gastrointestinal cell lines tested. Although cell proliferation is inhibited by gastrin/CCK receptor antagonists, the spectrum of antagonist affinities is not consistent with binding to either CCK-A or gastrin/CCK-B receptors. Definition of the molecular structure of the receptor involved in the autocrine loop may lead to novel therapies for gastrointestinal cancer.     

The mechanism of hypergastrinemia in achlorhydria. Effect of food, acid, and calcitonin on serum gastrin concentrations and component pattern in pernicious anemia, with correlation to endogenous secretin concentrations in plasma.

The effect of protein-rich food, intravenous calcitonin injections, and intragastric instillation of hydrochloric acid on serum gastrin concentrations and gastrin component pattern was studied in hypergastrinemic patients (pernicious anemia) and matched control subjects. Moreover, plasma secretin concentrations were measured during intragastric acidification. The intragastric acidification resulted in rapid fall in serum gastrin concentrations, although not below the upper limit of normal range. The small components, III (gastrin-17-like) and IV (gastrin-13-like), almost disappeared, whereas the concentrations of component I and component II (gastrin-34-like) were less affected. The increase in secretin concentrations after intragastric acidification was smaller in patients with pernicious anemia than in normal subjects, although the difference was not significant. In contrast to the results in normal control subjects, neither food nor calcitonin produced significant variations in serum gastrin concentrations and gastrin component pattern of pernicious anemia patients. The failure of food to stimulate and of calcitonin to inhibit release of gastrin in the majority of pernicious anemia patients might suggest that gastrin secretion in these patients is autonomous. However, considering the recently recognized slow metabolic clearance rate of big gastrins, the effect of intragastric acidification suggests that the mechanism for acid inhibition of the antral gastrin secretion is intact in patients with achlorhydria.     

Carboxyl terminal glycine extended progastrin (gastrin-G) in gastric antral mucosa of patients with gastric or duodenal ulcer and in gastrinomas

Recently, carboxyl terminal glycine extended progastrin (gastrin-G), the immediate biosynthetic precursor of amidated gastrin, was found in human gastric antral mucosa. To investigate in pathophysiological conditions, we examined gastrin and gastrin-G levels and their molecular forms in gastric antral mucosa of healthy controls and patients with gastric or duodenal ulcer and in gastrinomas. There were no significant differences between controls and gastric or duodenal ulcer patients in antral gastrin and gastrin-G levels, the ratio of gastrin-G to gastrin and the pattern of their molecular forms. In contrast, gastrin and gastrin-G levels and the ratio of gastrin-G to gastrin in gastrinomas were much higher than those in antral mucosa of controls or ulcer patients. The predominant molecular form of gastrin-G was different between two Zollinger-Ellison syndrome (ZES) cases. These results suggest that there are no significant differences between healthy controls and patients with gastric or duodenal ulcer in the nature of gastrin amidation, and that the nature of gastrin amination in gastrinomas is different from that in normal gastrointestinal tissues.     

Plasma levels of progastrin but not amidated gastrin or glycine extended gastrin are elevated in patients with colorectal carcinoma

BACKGROUND: The relationship between plasma gastrin levels and colorectal cancer is controversial. When confounding factors which increase plasma gastrin levels are taken into account, it has been shown that gastrin levels are not elevated in patients with colorectal cancer. However, these studies only measured amidated gastrin. Total gastrin (which includes unprocessed, partially processed, and mature forms of gastrin) has been shown to be elevated in patients with colorectal cancer. AIMS: The aim of this study was to determine whether fasting plasma levels of progastrin, amidated gastrin, or glycine extended gastrin are elevated in patients with colorectal cancer or colorectal polyps compared with controls. METHODS: Progastrin, amidated gastrin, and glycine extended gastrin were estimated by radioimmunoassay using the following antibodies: L289, 109-21, and L2. Blood samples were analysed for Helicobacter pylori by an enzyme linked immunosorbent assay. RESULTS: Median progastrin levels were significantly higher in the cancer group (27.5 pmol/l) than in the polyp (< or =15 pmol/l) or control (< or =15 pmol/l) group (p=0.0001 There was no difference in median levels of amidated gastrin between groups. Median levels of amidated gastrin were significantly higher in H pylori positive patients (19 pmol/l) than in H pylori negative patients (8 pmol/l) (p=0.0022). Median plasma progastrin levels were significantly higher for moderately dysplastic polyps (38 pmol/l) compared with mildly dysplastic (15 pmol/l) and severely dysplastic (15 pmol/l) polyps (p=0.05). CONCLUSIONS: Plasma levels of progastrin, but not amidated gastrin or glycine extended gastrin, are significantly elevated in patients with colorectal cancer compared with those with colorectal polyps or controls, irrespective of their H pylori status. We conclude that measuring plasma progastrin levels in patients with colorectal cancer is warranted.     

Regulation of gastric function by endogenous gastrin releasing peptide in humans: studies with a specific gastrin releasing peptide receptor antagonist

BACKGROUND AND AIMS: The main goal of our study was to characterise the activity of BIM26226 as a peripheral gastrin releasing peptide (GRP) receptor antagonist in healthy human subjects and to determine if endogenous GRP is a physiological regulator of gastric acid secretion and gastrin release. METHODS: Our study consisted of three parts. In part I, subjects received saline or BIM26226 followed by graded doses of intravenous human GRP in a four period crossover design. In part II, subjects received BIM26226 or saline during oral meal ingestion or modified sham feeding. In part III, subjects received an acidified meal in the presence and absence of BIM26226 in a two period crossover design. In addition, gastrin and somatostatin mRNA were measured in biopsy specimens during saline and BIM26226 infusion. RESULTS: BIM26226 dose dependently inhibited GRP induced acid output. Acid secretion after oral liquid meal intake and sham feeding was significantly inhibited by BIM26226 (p<0.01) whereas plasma gastrin release remained unchanged. Gastrin and somatostatin mRNAs were not significantly different after saline or BIM26226. CONCLUSIONS: BIM26226 is a potent GRP antagonist in humans. Endogenous GRP may be a physiological regulator of gastric acid secretion. Gastrin release does not seem to be under the control of GRP.     

Progastrin stimulates murine colonic epithelial mitosis after DNA damage

BACKGROUND & AIMS: Transgenic mice that overexpress progastrin are more susceptible than either wild-type mice or mice that overexpress amidated gastrin to chemical carcinogen-induced colonic adenomas. We have investigated whether alterations in the regulation of apoptosis or mitosis after DNA damage contribute to the effects of progastrin on murine colonic epithelium. METHODS: Apoptosis and mitosis were assessed on a cell positional basis in murine intestinal epithelium after gamma-irradiation. Mice analyzed were progastrin overexpressing, gastrin overexpressing, gastrin knockout, and their wild-type counterparts. The expression of cell cycle regulators was analyzed by gene array and Western blotting. RESULTS: Apoptosis was induced to similar levels in the small intestinal and colonic crypts of all mice 4.5 hours after 8 Gy gamma-radiation. Colonic mitosis was inhibited to almost undetectable levels by 8Gy gamma-radiation in wild-type, gastrin-knockout, and gastrin-overexpressing mice. However, significant colonic mitosis persisted in progastrin-overexpressing mice up to 24 hours after 8Gy gamma-radiation. Increased levels of cdk4 and cyclin D1 proteins were found in the colonic epithelium of progastrin-overexpressing mice relative to wild-type animals after gamma-radiation. CONCLUSIONS: After DNA damage by gamma-radiation, mice with elevated progastrin exhibit significantly higher levels of colonic mitosis than wild-type or gastrin-overexpressing mice. Persistently elevated cdk4 and cyclin D1 in progastrin overexpressing mice accounts for the capacity of colon cells to continue with the cell cycle after DNA damage.     

The ultimate biochemical diagnosis of endocrine pancreatic tumours in MEN-1

Öberg K, Skogseid B (University Hospital, Uppsala, Sweden). The ultimate biochemical diagnosis of endocrine pancreatic tumours in MEN-1 (Minisymposium: MEN & VHL). J Intern Med 1998; 243 : 471–6. Multiple endocrine neoplasia type 1 (MEN-1) is a well characterized hereditary syndrome with the occurrence of primary hyperparathyroidism (HPT) in combination with pancreatic-duodenal endocrine and anterior pituitary tumours. The diagnosis of MEN-1, the possible probands, necessitates the recognition of at least two or three lesions classically associated with the syndrome whilst only one of them is required for individuals belonging to established MEN-1 kindreds. A distinct feature of MEN-1 comprises the multiplicity of organ involvement, the multicentricity of tumours within the affected organs as well as the complex pattern of the clinical signs of these tumours and their sometimes temporarily variable profile of hormone excess. Thorough screening studies have demonstrated that the MEN-1 trait is biochemically detectable virtually two decades prior to clinically overt disease. The primary biochemical screening programme for MEN-1 includes serum prolactin and insulin growth factor 1 (IGF-1) for pituitary lesions, intact PTH and albumin corrected total serum calcium for the parathyroids and for duodenal/pancreatic tumours serum glucose, insulin, proinsulin, pancreatic polypeptide, glucagon, gastrin and plasma chromogranin A. Furthermore a standardized meal stimulatory test analysing serum polypeptides (PP) and gastrin is recommended. Our current primary screening procedure has yielded about 10% false positives when compared with RFLP data. Pancreatic endocrine tumour diagnosis must be biochemically established since radiology fails to show lesions in half of the patients. Pancreatic involvement in young MEN-1 patients is most consistently demonstrated by analysing serum insulin, proinsulin, PP as well as plasma glucagon chromogranin A levels, which have exhibited sensitivities of 56, 67, 37 and 60%, respectively. Serum PP is a non-specific marker of islet cell tumours that should be applied in conjunction with other peptide markers. Elevation of basal serum gastrin generally indicates the presence of advanced pancreatic tumour involvement or duodenal carcinoids. Early diagnosis of pancreatic endocrine tumours in MEN-1 is enhanced by the use of a standardized meal stimulation test with measurements of serum PP and gastrin response. This test was the most sensitive test and substantiated the presence of tumour in 75% of individuals whose mean age was 25 years. False-positive stimulation due to the meal test has been found in about 10% of previous investigated individuals. The diagnosis of MEN-1 pancreatic tumours is based on biochemical screening alone and it has been substantiated that an unequivocal rise in pancreatic tumour markers precedes radiological detection of these lesions by at least five years.     

Peptide α-amidation activity in human plasma: relationship to gastrin processing

OBJECTIVE AND DESIGN C-terminal amidation is an essential processing step towards bioactivation of many peptides including gastrin. This reaction is catalysed by peptidylglycine α-amidating mono-oxygenase (PAM, EC 1.14.17.3) which converts the glycine extended precursors on their carboxyl termini to the des-glycine amidated peptide products. In the case of gastrin, most of the amidation is thought to occur in the antrum. However substantial quantities of glycine extended gastrin and PAM are present in plasma. It is unclear whether circulating PAM reflects the secretory activity of the gastrin secreting cell or whether PAM is involved in the post-secretory processing of gastrin. The aim of the present study was to relate the circulating amidation activity to the plasma concentrations of glycine extended and amidated gastrins. PATIENTS AND MEASUREMENTS Plasma PAM, gastrin-amide and gastrin-gly were measured in subjects with different gastrin secretory status: healthy subjects basally and following a meal, members of families with multiple endocrine neoplasia type 1 (MEN-1) with normal and high plasma gastrin, and patients with hypergastrinaemic atrophic gastritis. RESULTS Patients with MEN-1 and hypergastrinaemia tended to have a higher plasma PAM activity than MEN-1 subjects with normal circulating G-NH₂ indicating a co-secretion of hormone and PAM. However in contradistinction to patients with medullary thyroid carcinoma, PAM activity does not appear to be a useful tumour marker of gastrinoma. Hypergastrinaemia from a non-tumour source (hypergastrinaemic non-atrophic gastritis) was associated with a lower plasma PAM activity than in normal subjects and may reflect the secretion of a greater proportion of already amidated gastrin. In general, there was no relationship between plasma PAM activity and the ratio of amidated to non-amldated gastrin suggesting that circulating PAM was not involved in the amidation of gastrin. Feeding increased circulating gastrin but had no effect on plasma PAM activity. CONCLUSION The results support the view that gastrin is amidated at the site of its synthesis and that hypergastrinaemia is associated with elevated plasma amidating enzyme activity only when the gastrin originates from tumour sources.     

Glycine-extended processing intermediates of gastrin and cholecystokinin in human plasma

The biosynthesis of biologically active gastrin and cholecystokinin (CCK) requires the formation of carboxyl-terminally amidated peptides from glycine-extended precursors of gastrin and CCK. In previous studies we and others have identified and characterized glycine-extended forms of gastrin (Ggly) and CCK (CCK-gly) in the human gastrointestinal tract. To explore the potential biologic importance of these peptides in humans, we examined their release into the circulation. Ingestion of a standard meal induced a biphasic rise in plasma G/CCK-gly concentration, but only the initial increase correlated with gastrin release. Intraduodenal lipid infusion caused a selective rise in CCK-gly immunoreactivity with no increase in gastrin or G-gly. Gel filtration chromatography revealed that the predominant molecular form of G/CCK-gly in basal plasma coeluted with CCK8-gly, but in response to meal stimulation, increases in other molecular forms were noted. Measurement of glycine-extended intermediates of progastrin and procholecystokinin posttranslational processing in plasma may aid in determining their physiologic importance in health and disease.     

Gastrointestinal secretory, motor, circulatory, and metabolic effects of prosomatostatin.

This study compares the gastrointestinal effects of somatostatin (SS) and its putative prohormone, prosomatostatin (Pro-SS), a 28-amino acid peptide isolated from the hypothalamus and the gut, in conscious dogs with chronic gastric and pancreatic fistulae. Pro-Ss suppressed the release of serum gastrin, insulin, and pancreatic polypeptide that occurs in response to feeding a meat meal in a manner similar to that seen with SS. However, in contrast to SS, which strongly reduced intestinal blood flow and oxygen consumption and stimulated intestinal motility, Pro-SS, at the doses tested, had no influence on mesenteric circulation, oxygen uptake, and intestinal motility. We conclude that Pro-SS mimics most of the gastrointestinal secretory actions of SS, but does not exhibit the intestinal circulatory, metabolic, and motor effects of SS.     

Identification of progastrin derived peptides in colorectal carcinoma extracts.

The possible production of gastrin by colorectal carcinomas has been studied. Extracts of 44 tumours and adjacent macroscopically normal tissue were examined in radioimmunoassay using the following antibodies: (i) L289 raised to a C-terminal fragment of progastrin which shows specificity for intact progastrin, but not the extreme C-terminal tryptic peptide; (ii) LW60 raised to a C-terminal fragment of progastrin which reacts with progastrin and its C-terminal tryptic peptide; (iii) 109-21 which was raised to, and reacts with, Gly-extended forms of heptadecapeptide gastrin--that is, biosynthetic intermediates on the pathway producing active gastrin; and (iv) L2 which reacts with amidated, biologically active gastrins. All samples contained detectable material in assays using LW60; in general, concentrations measured with this antibody were higher than with the other antibodies, and in particular there were higher concentrations in tumour compared with normal tissue extracts. Tumour extracts also contained higher concentrations of immunoreactivity compared with normal tissue, in assays using antibodies L289 and 109-21. In contrast, amidated gastrins were found in similar concentrations in tumour and normal tissue, and concentrations were the lowest of those recorded in the four assays. Separation on Sephadex G50 revealed peaks compatible with progastrin and its C-terminal flanking peptide, and two other peaks that are so far unidentified. In conclusion most colorectal carcinomas contain peptides derived from the gastrin precursor, progastrin, but for the most part these tumours do not convert progastrin into biologically active products.     

Gastroesophageal Sphincter Pressure and Serum Gastrin: Reaction to Food Stimulation in Normal Subjects and in Patients with Gastric or Duodenal Ulcer

Gastroesophageal sphincter pressure and serum gastrin concentration were determined in the fasting state and after the intake of a protein food in 6 normal subjects, 6 patients with gastric ulcer, and in 6 patients with duodenal ulcer. No significant differences in the fasting state were found. After the food intake, gastroesophageal sphincter pressure increased significantly over basal values in normals and in patients with duodenal ulcer, but in patients with gastric ulcer a decrease in pressure was noted. Serum gastrin rose in all subjects studied after the food stimulation, but it was significant only in the gastric and duodenal ulcer group. In two normals and two patients with duodenal ulcer the ingestion of a potato meal of similar weight to that of the protein meal showed no change either in serum gastrin or in sphincter pressure. In one additional normal subject and one duodenal ulcer patient the constant intravenous infusion of Aminosol for 2 h produced no change in serum gastrin or sphincter pressure. These results indicate that the effect of protein food on sphincter pressure is different for gastric or duodenal ulcers, and, furthermore, that this effect is mediated by proteins in the gastrointestinal tract.     

Augmented gastrin responses in diabetic patients with vagal neuropathy

Summary We evaluated serum gastrin responses to a test meal in normal subjects and diabetic patients with or without vagal neuropathy. Vagal neuropathy was defined as a heart rate variation during deep breathing of < 9 beats/min. Forty-three percent (54 out of 124) of the diabetic patients had abnormal heart rate variation, compared with 5% (3 out of 53) of the normal subjects. Serum gastrin responses to a test meal were examined in 17 normal subjects, 20 out of 70 diabetic patients without vagal neuropathy and 17 out of 54 diabetic patients with vagal neuropathy. Meal-stimulated gastrin levels were significantly higher in the diabetic patients with vagal neuropathy than in the normal subjects, while the findings in the diabetic patients without vagal neuropathy were similar to those in normal subjects. These data suggest that augmented gastrin responses are due to vagal denervation induced by autonomic neuropathy.     

Progastrin in serum from Zollinger-Ellison patients. An indicator of malignancy?

Progastrin and all of its processing products were measured in serum from 48 patients with Zollinger-Ellison syndrome, 42 patients with duodenal ulcers, and 34 normal subjects. A processing-independent gastrin analysis and a conventional radioimmunoassay for the biologically active alpha-amidated gastrins were used. In serum from normal subjects, 87% (median; range, 27%-160%) of all progastrin products were alpha-amidated gastrins, whereas they constituted only 39% (15%-130%) in serum from patients with duodenal ulcers (p less than 0.01) and 46% (16%-100%) in serum from gastrinoma patients (p less than 0.01). A significantly lower percentage of alpha-amidated gastrin was found in patients with hepatic metastases (23%) than in patients with apparently benign tumors (54%). Chromatography of serum showed that large progastrin molecules occurred mainly in patients with malignant tumors, whereas smaller glycine-extended precursors dominated in patients with benign tumors. The results indicate that the total progastrin product reflects tumor synthesis of gastrin better than conventional measurements of alpha-amidated gastrin. Moreover, the results suggest that a low degree of processing of progastrin could serve as a predictor of a malignant clinical course at an early stage of the disease.