Regulation of intestinal proglucagon-derived peptide secretion by intestinal regulatory peptides.

The physiological regulation of intestinal proglucagon-derived peptide secretion has not been well studied. We have therefore used a fetal rat intestinal cell culture model to investigate the control of secretion of the gut glucagon-like immunoreactive (GLI) peptides by other intestinal regulatory peptides in vitro. Secretion of the intestinal GLI peptides was found to be stimulated in a dose-dependent fashion by the intestinal endocrine peptide, gastric inhibitory peptide (at greater than or equal to 10(-10) M, P less than 0.05), and by the neurocrine peptides, gastrin-releasing peptide (at greater than or equal to 10(-12) M, P less than 0.05), and calcitonin gene-related peptide (at greater than or equal to 10(-8) M, P less than 0.05). Gastrin-releasing peptide and its amphibian equivalent, bombesin were equipotent in stimulating GLI peptide secretion. In contrast, the endocrine and neurocrine intestinal somatostatin-related peptides, somatostatin-28 and -14, inhibited release of the GLI peptides, at concentrations of 10(-10) (P less than 0.01) and 10(-8) (P less than 0.01) M, respectively, with significant differences in potency between the two peptides detected at 10(-10) M (P less than 0.05). The inhibitory effects of both somatostatin-28 and -14 could be blocked by preincubation of the cells with pertussis toxin (P less than 0.05). Dose-dependent stimulation of gut GLI peptide secretion was also detected in response to treatment of cultured cells with sodium oleate (at 10(-4) M; P less than 0.05), or with the cholinergic agonist bethanecol (at greater than or equal to 100 microM; P less than 0.05). Other endocrine [cholecystokinin, glucagon, glucagon-like peptide-1(1-37), glucagon-like peptide-1(7-37), glucagon-like peptide-2, neurotensin, and peptide YY] and neurocrine (vasoactive intestinal peptide) peptides, and the synthetic glucocorticoid, dexamethasone, were without effect on secretion of the gut GLI peptides, at doses of 10(-12) to 10(-6) M. The results of the present study therefore demonstrate that secretion of the intestinal proglucagon-derived peptides is under the regulatory control of a wide variety of intestinal endocrine and neurocrine peptides, as well as nutrients (fats) and neurotransmitters (acetylcholine).     

Evidence for the presence of glucagon-like immunoreactivity (GLI) in the pancreas.

Glucagon-like immunoreactivity (GLI), which can be separated from glucagon by isoelectric focusing, has been detected in partially purified canine pancreatic extracts. Like gastrointestinal GLI, this insular GLI reacts with crossreacting antiserum 78J but not with glucagon "specific" antiserum 30K and has an isoelectric point (pl) of 9.5, whereas canine pancreatic glucagon has a pl of 6.25. When combined with glucagon, the GLI-glucagon mixture gives 48J assay values between GLI and this crossreacting antiglucagon serum and thus conceals it in glucagon-containing extracts.     

Control of glucagon-like immunoreactive peptide secretion from fetal rat intestinal cultures

Some of the mechanisms underlying intestinal glucagon-like immunoreactive (GLI) peptide secretion from cultured fetal rat intestinal cells were investigated using modulators of the adenylate cyclase pathway [(Bu)2cAMP, theophylline, isobutylmethylxanthine], calcium fluxes (ionomycin, A23187), and protein kinase-C (phorbol ester). All of these agents were found to stimulate GLI peptide release, to 120-230% of paired control values (P less than 0.05-0.001). (Bu)2cAMP, but not the phorbol ester, also increased the total cell content of GLI peptides over the 2-h incubation period (P less than 0.05). No synergism between any of the three pathways was detected. When the mol wt distribution of the stored and secreted GLI peptides was determined in control and (Bu)2 cAMP-stimulated samples, 68 +/- 2% of the peptide corresponded to glicentin, while the remainder eluted with the same distribution coefficient as oxyntomodulin. No 3.5K glucagon was detected in any of the extracts. GLI peptide secretion by the cells was not altered by several pancreatic glucagon secretagogues (cortisol, bombesin, and prostaglandins E1 and D2), but was stimulated by the opioid peptide beta-endorphin (1 microM; P less than 0.02). These studies have indicated that the control of secretion of fetal rat intestinal GLI peptides is complex, involving activation of any one or a combination of the three major second messenger systems. A role for the adenylate cyclase pathway in regulating GLI peptide biosynthesis is also suggested.     

Glucagon-like immunoreactive peptides in a rat ileal epithelial cell line (IEC-18)

The presence of cells containing glucagon-like immunoreactive (GLI) peptides was demonstrated in a rat ileal epithelial cell line (IEC-18) by both immunofluorescence and radioimmunoassay. When cell extracts were subjected to gel filtration chromatography, the cells were found to contain 3.5 Kd glucagon in addition to significant quantities of large molecular weight GLI peptides (apparent molecular weights of 4, 6, 8 and 10 Kd) and a 9 Kd peptide with apparent glucagon immunoreactivity. This was in contrast to extracts of adult rat ileum, which contained only large molecular weight GLI peptides (apparent molecular weights of 6 and 12 Kd). Production of GLI peptides by the IEC-18 cells was stimulated by glucose (p less than 0.02) and inhibited by insulin (p less than 0.01). In conclusion, these results demonstrate that the IEC-18 cells produce both GLI peptides and glucagon, and thus support the notion that proglucagon processing is cell-specific. IEC-18 cells may therefore provide a tool for investigations of some aspects of GLI peptide and glucagon synthesis.     

Distribution of oxyntomodulin and glucagon in the gastrointestinal tract and the plasma of the rat

Oxyntomodulin (OXM), an intestinal glucagon-containing peptide extended at its C-terminal end by an octa-peptide, is one of the gut glucagon-like immunoreactants (GLI) or enteroglucagon. The distribution of OXM and glucagon was determined in the gastrointestinal tract and in the plasma of the rat. Reversed-phase HPLC, associated with RRA or RIA, performed with an N-terminally directed glucagon antiserum (GOL), was used. HPLC of intestinal extracts or plasma separated the GOL immunoreactivity into three peaks: two major peaks coeluting with a preparation of rat glicentin (peak I, partially purified from rat intestine) and porcine or rat OXM, respectively, and a smaller peak coeluting with glucagon. The behavior of the three peaks in the analytical systems matched that of glicentin, OXM, and glucagon, respectively, allowing their identification. The concentrations of OXM picomoles per g of tissue) gradually increased from the duodenum (9 +/- 1) to ileum (93 +/- 4), thereafter decreasing in cecum and colon (22 +/- 3). In the gut, OXM, glucagon, and peak I averaged 40%, 1%, and 59% of the total GLI, respectively. OXM was present in significant amounts in the pancreas (18% of GLI) and stomach (27% of GLI), two tissues in which it accounted, together with glucagon, for almost the totality of GLI. In 24 h-fasted rats, plasma concentrations of OXM, glucagon, and peak I, determined after HPLC with GOL antiserum, were 15.1 pM, 8.6 pM, and 12.3 pM, respectively. Two hours after refeeding, both OXM and peak I were significantly increased (P less than 0.05 and P less than 0.02) by a similar factor (2-fold), while glucagon remained unchanged. When the HPLC results were compared with RIA measurement of GLI (GOL antiserum) and glucagon (with a C-terminal glucagon antiserum) in plasma, enteroglucagon (GOL--C-terminal glucagon antiserum immunoreactivities) correlated well with the sum of OXM plus peak I. The combination of HPLC and RRA or RIA allows the unambiguous determination of OXM, glucagon, and glicentin (peak I) in tissues and plasma. In the rat intestine and in the plasma, OXM and glicentin appear roughly in the same ratio and seem to be the major components, if not the totality, of enteroglucagon.     

Extrapancreatic glucagons.

From the mucosa of the gastrointestinal tract a number of peptides can be extracted, which are glucagon-like in their behavior towards antisera raised against the pancreatic hormone. The biochemistry and physiology of these peptides are critically reviewed. Although important advances have been made, facilitated by improved praparative and analytical techniques, many problems remain unresolved. It is, however, now well established that a peptide, which is indistinguishable from true, pancreatic glucagon (NW 3,485) is found in extrapancreatic gastrointestinal tissue from all species investigated. While abundant in dogs, especially in the gastric mucosa, much less is found in extra-pancreatic tissues of man and pig. Results from studies in dogs are therefore not necessarily relevant to other species. Human and porcine gut, however, contain other glucagon-like peptides (gut-type glucagon, enteroglucagon, gut GLI), one of which resembles true glucagon (MW 3,485) in its biological activity, but a definite physiological role for these peptides has not yet been established. The recent isolation and purification of one of the latter peptides undoubtedly will facilitate greatly future research in this field.     

Oxyntomodulin and glicentin: brain-gut peptides in the rat

Glucagon-like materials and glucagon have been identified by immunoassay and immunocytochemistry in the mammalian central nervous system. However, the molecular forms relevant to brain glucagon-like immunoreactivity (GLI) have not been precisely defined. In the rat small intestine, more than 90% of GLI is constituted by two peptides: oxyntomodulin (OXM) and glicentin. This work was initiated to characterize and determine the concentrations of these two peptides and glucagon in the rat central nervous system and to compare their relative proportions with those found in the gut. Different regions from the adult rat brain were analyzed by HPLC in association with RIA, using a central glucagon antiserum and an antibody directed toward the C-terminal end of OXM and glicentin. The elution profiles of hypothalamus extracts were constituted by two main peaks, both detected by the two antibodies used and displaying the same retention times as glicentin and OXM, respectively. A third small peak, which coeluted with glucagon, was constantly recorded with the central glucagon antiserum. The percentages of glicentin, OXM, and glucagon in 10 hypothalami were 37 +/- 1%, 55 +/- 1%, and 8 +/- 2%, respectively (n = 8). This distribution was quite similar to that in small intestinal extracts (38 +/- 1%, 59 +/- 1%, and 1.3 +/- 0.1%, respectively; n = 7); however, the peptide concentrations were almost 50-fold greater in intestine than in hypothalamus. In the medulla oblongata, the same peptide ratio was observed, with 10-fold lower concentrations compared to those in hypothalamus. In olfactory bulb, cerebellum, and cortex the concentrations were close the the detection limit, whereas they could be not detected in the pituitary. The combination of HPLC and specific RIAs allowed us to unambiguously characterize OXM and glicentin as the major components of GLI in the rat hypothalamus and medulla oblongata. The same proportion of these two peptides in the central nervous system and the gut indicates that a similar posttranslational processing exists in these rat tissues, another example of the brain-gut axis.     

Brain/gut peptides in fed and fasted rats

The concentrations and contents of vasoactive intestinal peptide (VIP) and cholecystokinin (CCK) in the brain and of these peptides along with secretin and glucagon-like immunoreactivity (GLI) in the gut were compared in a group of 16 5-day fasted adult Sprague-Dawley rats with the corresponding peptides in a group of 16 nonfasted littermates. The mean weight of the fasted rats at the beginning of the study was 263 +/- 10 g (+/- SEM) and was 177 +/- 7 g before killing, for a net loss of 33% of initial body weight; the 16 fed rats increased their mean weight from 225 +/- 11 to 284 +/- 12 g, for a net gain of 12%. During the 5-day fast there was no change in the weight of the cortex, hypothalamus, or brain stem. However, the weight of tissues from the gut decreased to about half the weight of the corresponding tissues in the fed animals. There was no significant change in brain VIP or CCK. VIP content in the gut was unchanged. However, because of the decrease in organ weight, its concentration almost doubled. Secretin concentrations in the gut of fasted rats did not change significantly, but organ contents fell to about half. The gut content of GLI also fell by half or more. The concentrations of CCK in methanol extracts of the duodenum and jejunum remained relatively constant, but those in acid extracts fell by 40% in the fasted animals. This represents an approximately 70% decrease in organ content of CCK. These findings are interpretable as demonstrating that during a prolonged fast neuronal CCK and VIP are well conserved, but endocrine CCK, secretin, and GLI are markedly decreased because of loss of intestinal mucosa.     

Fetal rat intestinal cells in monolayer culture: a new in vitro system to study the glucagon-like immunoreactive peptides

To establish an in vitro model to investigate the glucagon-related peptides, fetal rat intestinal cells were enzymatically dispersed and placed into culture for up to 7 days. After 1 day in culture, the presence of epithelial-like cells containing glucagon-like immunoreactivity (GLI) was demonstrated using immunocytochemical techniques. The cell peptides were extracted by passage through a cartridge of octadecylsilyl silica and characterized by gel filtration and RIA. Two GLI moieties were detected with apparent mol wts of 11,000-12,000 and 5,000-6,000. The immunoreactive profile obtained for the cells in culture was identical to that of both whole fetal rat intestine and adult rat ileum. The presence of glucagon could not be demonstrated in any of the extracts. The basal levels of GLI and apparent immunoreactive glucagon (IRGa) were 1,457 +/- 381 and 198 +/- 57 pg/dish, respectively, on day 1 of culture. The GLI content of the cells, but not the IRGa, declined with time in culture for up to 5-7 days (P less than 0.03). Addition of insulin to the culture medium (10 or 100 mU/ml) did not influence the decrease in GLI content of the cells, but did inhibit the production of IRGa (P less than 0.05). Addition of 500 mg/dl glucose to the cells in the presence of 20 microU/ml insulin increased the secretion of GLI by 42 +/- 7% over 2 h (P less than 0.05). The stimulation by glucose was not seen in the absence of insulin or with higher insulin concentrations (100 microU/ml), nor did insulin alone (100 microU/ml) have any effect on the release of GLI. Thus, fetal rat intestinal cells in culture produce the GLI peptides, and secrete them in response to glucose. This system may provide a means by which the synthesis and control of secretion of the glucagon-related peptides can be investigated.     

Simultaneous recording of the gastro-entero-pancreatic hormonal peptide response to food in man

The serum or plasma concentrations of gastrin, gastric inhibitory polypeptide (GIP), gut glucagon-like-immunoreactivity (gut GLI), secretin, vasoactive intestinal polypeptide (VIP), insulin, glucagon, and pancreatic polypeptide (PP) were recorded simultaneously following the ingestion of a normal, mixed meal in seven healthy, normal weight men. The concentrations of PP and gastrin increased within 10 min. Subsequently GIP, insulin, glucagon, and gut GLI increased in the order mentioned. The mean concentrations of secretin and VIP were not affected by the meal, although transient decreases in secretin concentrations could be detected in all subjects. The concentrations of the other hormones remained elevated for 4 hr or more. Perhaps the period of observation following food stimulation of gastroentero-pancreatic hormones should be extended.     

The effect of phenformin upon the plasma pancreatic and gut glucagon-like immunoreactivity in diabetics

Five patients with mild maturity-onset diabetes were given 250 ml of a 20% glucose solution by intraduodenal infusion and eight other patients similarly received an amino acid solution in a dose of 0.5 g amino acids per kg body weight. The pancreatic and gut glucagon-like immunoreactivity (pancreatic GLI and gut GLI) in plasma were measured before and after the application of the two stimuli. Each person was tested twice; the first (control) test was followed by a second test after three days of treatment with phenformin 150 mg daily, plus the same 150 mg dose taken 60 min before the intubation. The plasma pancreatic GLI increased slightly during both infusions, but was not affected by phenformin. Intraduodenal infusion of both glucose and the amino acid solution induced a greater rise in plasma gut GLI. After treatment with phenformin, the fasting plasma gut GLI was higher than the control value in eleven of thirteen patients. In most cases higher gut GLI plasma levels were also found after duodenal administration of glucose and amino acids. These data furnish further evidence of the local action of antidiabetic biguanides on the intestinal wall, including its hormonal activity. The hypothesis is advanced that the phenformin-induced increase in gut GLI secretion may bring about competition of the latter with pancreatic glucagon for receptors in liver cell membranes, reducing the effect of glucagon on the liver, and thus contributing to a decrease in glycaemia.     

Production and characterization of N-terminally and C-terminally directed monoclonal antibodies against pancreatic glucagon

Hybridoma technology has been successfully applied to the production of monoclonal antibodies against a variety of small soluble peptides. We report herein for the first time on the development of monoclonal antibodies to pancreatic glucagon. Twenty-three stable positive hybridomas were detected by radioimmunoassay from five separate fusions and cloned by the limiting dilution method. Four selected monoclonal antibodies were all of the IgG 2a subclass type kappa and bound to protein A. One monoclonal antibody (23.8B6) was shown to be directed toward the C-terminal region and another (23.6B4) toward the N-terminal to central region of the glucagon molecule. These antibodies did not cross-react with any of the other peptides tested. Two further monoclonal antibodies (23.4A1, 22.3A6) reacted with the C-terminal third of the glucagon molecule and showed a cross-reaction with the structurally related gastric inhibitory polypeptide of 0.7% and 9.1%, respectively. All but the C-terminal monoclonal antibody 23.8B6 showed a marked cross-reaction with ileal extracts. The N-terminally directed monoclonal antibody 23.6B4 was of sufficient avidity for use in the radioimmunoassay of pancreatic glucagon and gut glucagon-like immunoreactivity in tissue extracts, being sensitive to changes of pancreatic glucagon of 2.0 fmol/tube at a final titer of culture supernatant of 1:1.4 X 10(5). In gel permeation chromatography of intestinal extracts, two major peaks were detectable (Kav 0.27 and 0.54). The present findings show that monoclonal antibodies provide sensitive tools for detecting pancreatic glucagon and gut glucagon-like immunoreactivity. They will be valuable immunoreactants for the development of immunoradiometric assays as well as for large-scale immunoaffinity purification of gut glucagon-like immunoreactivity.     

Extraction,gel filtration pattern,and receptor binding of porcine gastrointestinal glucagon-like immunoreactivity

Summary Different techniques for the extraction and initial purification of porcine gastrointestinal glucagon-like immunoreactivity (GLI) were compared with reference to yield, and preservation of number and pattern of GLI components. The conventional acid-ethanol technique combined with ethanol-ether purification gave high yields and a reproducible pattern of components. Large amounts of tissue were more easily extracted using another technique, based on extraction by boiling, extraction and precipitation with acetone, and — if necessary — salting out. — By means of the latter two techniques mucosal tissue from all of the porcine gastrointestinal tract was extracted and subjected to gel filtration. Glucagon-like peptides were searched for using: — 1. a radioimmunoassay which quantifies gut type glucagon (GTG), as well as pancreatic type glucagon (PTG), 2. a radioimmunoassay highly specific for pancreatic type glucagon (PTG), and 3. a radioreceptor assay based on binding of glucagon to porcine liver cell membranes. — The oesophageal, the fundic, and the antro-pyloric parts of the gastric mucosa contained very small amounts of GLI. The cardiac gland region contained small amounts of a peptide indistinguishable from true glucagon. The duodenal mucosa contained small amounts of true glucagon and may be a smaller, glucagon-like peptide. The mucosa of the small intestine contained large amounts of both high and low molecular weight GTG and, in addition, PTG of high molecular weight and true glucagon. The colon also contained these components with true glucagon in high concentrations. Only small GTG and true glucagon were receptor-active, the former with less than its immunometric potency.     

Changes in glucagon processing occurring in the intestines of surgically stressed patients

BACKGROUND/AIMS: The kinetics of the pancreatic hormone glucagon in surgically stressed patients has not been investigated as thoroughly as that of insulin, despite its significant influence on energy metabolism in surgically stressed conditions. In the present study, we examined the kinetics of glucagon and glucagon-related peptides assessed by radioimmunoassay, and the molecular forms of these peptides using gel filtration chromatography, and in addition discuss glucagon processes in the pancreas and intestine in surgically stressed patients. METHODOLOGY: Ten patients who had undergone abdominal surgery for acute abdominal disorders were enrolled in this study (group S). Ten healthy volunteers were also enrolled as normal controls (group C). The serum level of glucagon and glucagon-related peptides were assessed in the early morning fasting state in both groups, on the second postoperative day in group S, using glucagon nonspecific N-terminal (glucagon-like immunoreactivity: GLI) and specific C-terminal (immunoreactive glucagon: IRG) radioimmunoassays. The molecular forms of these peptides were also estimated using the gel filtration chromatography method. RESULTS: Serum IRG in group S was significantly higher than that of group C (P < 0.05). Serum GLI was not significantly different between the two groups. In all patients except one in group S, a peculiar glicentin-like peptide (GLLP: MW about 8000) other than pancreatic glucagon was seen in gel filtration chromatography, which was not seen in group C. CONCLUSIONS: The kinetics and processing of glucagon in surgically stressed patients were quite different from those of healthy subjects. In surgically stressed patients, peculiar processing of glucagon occurred in the intestine, which was quite different from ordinary glucagon processing either in the pancreas or the intestine, generating GLLP.     

Does somatostatin in the gut inhibit the GLI release locally?

Summary Based on the assumption that somatostatin may inhibit peptide release through junctional complexes or through local circulation, an immunofluorescent technique for somatostatin and GLI in the gut was applied in order to investigate whether suppression of GLI release by i.v. administration of somatostatin was a physiological effect of somatostatin or not. Somatostatin-immunoreactive cells (GIF-cells) in the human and canine intestine had no direct cellular contacts with GLI-immunoreactive cells (GLI-cells). This finding suggests that somatostatin in the intestine does not inhibit GLI release through junctional complexes between GIF- and GLI-cells. As to the local circulation, most of GIF-cells in the canine intestine were distributed in the deeper portion of the intestinal gland which corresponds to the upstream sides of the local blood supply of the intestinal gland, as reported byReynold et al. The ratio of GIF-cells to total cells (GIF-cells + GLI-cells) was 68% in the duodenum and 25% in the ileum. In contrast, a limited number of GIF-cells was found in the human duodenum where a few GLI-cells were distributed and a few GIF-cells were seen in the human ileum where a large number of GLI-cells were located. Findings in the dog suggest the possibility that somatostatin inhibits GLI release from GLI-cells through the local circulation system of intestinal glands. However, findings in humans suggest that the same possibility does not apply to the human gut. Differences of population density of intestinal GIF-cells between humans and dogs indicate that the functional meaning of GIF-cells may vary from one species to another. GLI = glucagon like immunoreactivity.     

Changes in glucagon kinetics and processing in patients with acute pancreatitis

BACKGROUND/AIMS: The kinetics of the pancreatic hormone glucagon in patients with acute pancreatitis have not been investigated as carefully as those of insulin, in spite of its crucial influence on energy metabolism. In the present study, we studied the kinetics of glucagon and glucagon-related peptides assessed by radioimmunoassay. Furthermore, the molecular forms of these peptides were examined using gel filtration chromatography, and the glucagon processes in the pancreas and intestine in the early stage in patients with acute pancreatitis were investigated. METHODOLOGY: Fourteen patients with acute pancreatitis were enrolled in this study. Eight had severe pancreatitis (group S) and six had mild pancreatitis (group M). Ten healthy volunteers were also enrolled as the normal control (group C). Serum levels of glucagon and glucagon-related peptides were assessed on the second admission day in groups S and M, and in an early morning fasting state in group C, using glucagon non-specific N-terminal (glucagon-like immunoreactivity: GLI) and specific C-terminal (immunoreactive glucagon: IRG) radioimmunoassays. The molecular forms of these peptides were also estimated using gel filtration chromatography. We then discuss the glucagon processes based on these findings. RESULTS: Serum GLI and IRG in groups S and M were significantly higher than those of group C (P < 0.01), while those in group S were also significantly higher than those in group M (P < 0.05). In all patients in groups S and M, except for only three in group S, a peculiar glicentin-like peptide (GLLP: MW about 8000) other than pancreatic glucagon was observed in IRG gel filtration chromatography, which was clearly absent from group C. CONCLUSIONS: The kinetics and processing of glucagon in patients with acute pancreatitis were quite different from those of healthy subjects. In patients with acute pancreatitis, the peculiar processing of glucagon proceeded in the intestine quite differently from ordinary glucagon processing either in the pancreas or in the intestine, generating a peculiar GLLP.     

Glucagon-like peptides GLP-1 and GLP-2, predicted products of the glucagon gene, are secreted separately from pig small intestine but not pancreas

We developed specific antibodies and RIAs for glucagon-like peptides 1 and 2 (GLP-1 and GLP-2), two predicted products of the glucagon gene, and studied the occurrence, nature, and secretion of immunoreactive GLP-1 and GLP-2 in pig pancreas and small intestine. Immunoreactive GLP-1 and GLP-2 were identified in glucagon-producing cells of the pancreatic islets, and in glicentin-producing cells of the small intestine. Immunoreactive GLP-1 and 2 in intestinal extracts corresponded in molecular size to peptides synthesized according to the predicted structure. By reverse phase HPLC, intestinal and synthetic GLP-1 behaved similarly, whereas synthetic and intestinal GLP-2 differed. Pancreatic extracts contained a large peptide with both GLP-1 and GLP-2 immunoreactivity. Secretion was studied using isolated perfused pig pancreas during arginine stimulation, and isolated perfused pig ileum during either luminal glucose stimulation or vascular administration of the neuropeptide, gastrin-releasing peptide (GRP). Immunoreactive GLP-1 and GLP-2 were secreted in parallel with pancreatic glucagon and intestinal glicentin. The molecular forms of secreted immunoreactive GLP-1 and 2 corresponded to those identified in the tissue extracts.