Pancreatic Islet Hormone Research Articles

Regulation of glucagon and glucagon-like peptide-1 receptor messenger ribonucleic acid expression in cultured rat pancreatic islets by glucose, cyclic adenosine 3',5'-monophosphate, and glucocorticoids.

Glucagon and glucagon-like peptide-1 (GLP-1) are important regulators of glucose homeostasis, and both are involved in regulating pancreatic islet hormone secretion. Since the sensitivity of the endocrine pancreas to regulatory hormones can be influenced by their receptor number, we have examined the regulation of glucagon receptor and GLP-1 receptor messenger RNA (mRNA) expression in cultured rat pancreatic islets by various factors, including glucose, cAMP, and glucocorticoids. By ribonuclease protection assay we have demonstrated the expression of both glucagon and GLP-1 receptor mRNA in cultured rat islets. We observed a dose-dependent increase in glucagon receptor mRNA expression with increasing glucose concentrations: an approximately 3-fold increase in glucagon receptor mRNA in islets cultured in 22 mM glucose as compared to 3.5 mM glucose. GLP-1 receptor mRNA levels, on the other hand, were not affected by culturing the islets in low glucose concentrations; however, a small, but significant, decrease in GLP-1 receptor mRNA levels was detected when islets were cultured in 20 mM glucose. Forskolin and 3-isobuty-1-methylxanthine, which increase intracellular cAMP levels, caused a 75% reduction in glucagon receptor mRNA expression. Somatostatin 14 and 28, both of which can inhibit intracellular cAMP production, stimulated glucagon receptor mRNA expression by 40% and 75%, respectively. GLP-1 receptor mRNA levels remained unchanged under all conditions that altered intracellular cAMP levels. Finally, in islets cultured in the presence of 10 nM dexamethasone an approximately 50% decrease in both glucagon and GLP-1 receptor mRNA expression was observed. These results indicate that the expression of glucagon and GLP-1 receptor mRNA is differentially regulated in rat pancreatic islets and suggest that regulation of receptor mRNA expression may be an important mechanism for controlling the sensitivity of the islets to glucagon and GLP-1.

Gastrointestinal growth factors and pancreatic islet hormones during postoperative IGF-I supplementation in man

Gastrointestinal growth factors and pancreatic islet hormones during postoperative IGF-I supplementation in man

Neurons Containing Gastrin Releasing Peptide-Like Immunoreactivity in the Human Pancreas

Gastrin releasing peptide (GRP) is known to stimulate pancreatic enzyme and islet hormone secretion. In the present immunohistochemical study, the localization and distribution of GRP-like immunoreactivity were investigated in the human pancreas using two antisera with different specificities. GRP-like immunoreactivity (GRP-LI) was observed in numerous nerve fibers diffusely distributed to the exocrine pancreas, but was not seen in intrapancreatic nerve cells of normal pancreatic specimens examined. Nerve fibers and terminals with GRP-LI were found in abundance around pancreatic acini and capillaries, with moderate density around ductules and in the walls of arterioles, and a few were seen in islets. This distribution pattern was quite similar to that of vasoactive intestinal polypeptide (VIP)-LI nerve fibers. The study, using the antibody elution method, strongly suggests the co-localization of GRP- and VIP-LIs within a part of VIP-containing nerve fibers. In the chronic pancreatitis specimens, neurons with GRP-LI were frequently found, and > 90% of intrapancreatic nerve cells were VIP-immunoreactive. Immunostainings for GRP and for VIP on serial adjacent sections of intrapancreatic ganglia from chronic pancreatitis specimens suggested the co-localization of the two immunoreactivities in > 70% of intrapancreatic neurons. The present findings may provide a morphological basis for neurotransmitter and/or neuromodulator roles of GRP in the human pancreas.

Effect of islet hormones on secretin-stimulated exocrine secretion in isolated perfused rat pancreas

To clarify the effect of islet hormones on pancreatic ductular cell function, we measured the exocrine secretion elicited by 10 pM secretin in the presence or absence of islet hormones using an isolated perfused rat pancreas model. Insulin significantly increased secretin-stimulated pancreatic juice secretion, but not protein secretion. The potentiating effect of insulin on pancreatic juice secretion was concentration-dependent, and the maximal effect was observed with 1 microM insulin. Ouabain, a specific Na+,K(+)-ATPase inhibitor, caused concentration-dependent inhibition of the potentiating effect of insulin without affecting secretin action. Glucagon (100 nM) significantly inhibited secretin-stimulated pancreatic juice secretion and also tended to inhibit protein secretion. A somatostatin analog, SMS 201-995 (10 nM) significantly inhibited both the pancreatic juice and protein secretion stimulated by secretin. The inhibitory effect of SMS 201-995 was concentration-dependent and was maximal at 1-10 nM. These results demonstrate that insulin potentiates the secretory response to secretin, at least partly by increasing Na+,K(+)-ATPase activity, whereas glucagon and somatostatin inhibit this response. Thus, pancreatic islet hormones regulate the secretory function of pancreatic ductular and centroacinar cells.

Response to intravenous injections of amylin and glucagon in fasted, fed, and hypoglycemic rats.

The actions of intravenous glucagon and amylin, a newly discovered hyperglycemic pancreatic islet hormone, have been compared in 20-h fasted and fed, lightly anesthetized rats, and in rats made hypoglycemic with an insulin infusion. In fasted animals, amylin (75 nmol/kg) was more effective than glucagon (90 nmol/kg) in increasing plasma glucose (glucose increment 4.55 vs. 1.71 mM, P < 0.001). Amylin elicited a marked increase in plasma lactate, as previously reported, whereas glucagon did not alter plasma lactate. In fed animals, glucagon elicited twice as much increase in plasma glucose as did amylin; amylin again elicited a marked lactate increase that was greater (increment 1.45 vs. 0.97 mM, P < 0.05) and more prolonged than in the fasted state, whereas glucagon was without effect on lactate levels. These findings are consistent with glucagon's known action to promote hyperglycemia from hepatic glycogenolysis and amylin's demonstrated action to promote muscle glycogenolysis and increase lactate supply to the liver. Infusions of sodium lactate that produced plasma lactate increments similar to those evoked by 75 nmol/kg amylin evoked patterns of glucose response in fasted and fed rats similar to those evoked by amylin. Thus increased lactate supply to the liver may account for amylin's hyperglycemic effects. Amylin and glucagon could each restore plasma glucose to control levels in fasted animals made hypoglycemic by insulin infusion (plasma glucose reduced to 3.3 mM). A bolus of 75 nmol/kg amylin was more effective than 180 nmol/kg glucagon, restoring basal glucose levels for > 3 h, whereas glucagon restored it for < 1 h.(ABSTRACT TRUNCATED AT 250 WORDS)

In vitro inhibitory effect of somatostatin on secretin action in exocrine pancreas of rats

Background: Exocrine pancreatic function is influenced by pancreatic islet hormones. Although the existence of somatostatin receptors has been shown on pancreatic acinar cells, the in vitro effect of somatostatin on exocrine secretory function has not been established. Methods: Using isolated rat pancreatic acini, the effect of somatostatin analog SMS 201-995 (SMS) and somatostatin 14 (S-14) on amylase release, cyclic adenosine monophosphate (cAMP) production, and hormone binding were determined. Results: SMS inhibited the potentiating effect of secretin on amylase response to cholecystokinin octapeptide (CCK-8) in a concentration-dependent manner. The inhibitory effects of SMS and S-14 were similar on a molar basis and were observed when vasoactive intestinal polypeptide (VIP) but not 8bromoadenosine 3′:5′ cyclic monophosphate was used instead of secretin and when carbachol, bombesin, A23187, and 12-O-tetradecanoylphorbol 13-acetate were used instead of CCK-8. SMS inhibited secretin-induced cAMP production, and the dose-inhibition curve for cAMP was similar to that for amylase release. SMS had no influence on 125I-secretin and 125I-VIP binding. Conclusions: Somatostatin acts directly on acinar cells and inhibits secretin potentiation of secretory response in part by inhibiting secretin-induced cAMP production.

Abnormal plasma gut hormones in pathologic duodenogastric reflux and their response to surgery

Fasting and postprandial plasma levels of the gut hormones gastrin, cholecystokinin (CCK), secretin, glucose-dependent insulinotropic polypeptide, motilin, neurotensin, peptide YY (PYY), enteroglucagon, glucagon, insulin, and pancreatic polypeptide were measured in 11 patients with alkaline gastritis associated with excessive duodenogastric reflux not related to previous gastric surgery (primary DGR), 12 primary DGR patients after pancreatico-biliary diversion ("duodenal switch" procedure), and in 10 age-matched healthy controls. Gastric emptying of a semisolid oatmeal was also measured in patients with primary DGR and in patients after bile diversion. Fasting plasma levels of the distal gut hormone neurotensin and the pancreatic islet hormone insulin were significantly greater in patients with primary DGR compared with controls. Neurotensin levels were normal in patients studied after bile diversion. Postprandial plasma levels, incremental integrated and total integrated responses for CCK, secretin, insulin, neurotensin, PYY, and enteroglucagon, were significantly greater in patients with primary DGR compared with controls. The majority of these responses normalized after bile diversion; however, the postprandial response for insulin and enteroglucagon remained elevated. Patients with primary DGR had a rapid early postprandial phase of gastric emptying of solids, which showed a significant correlation with plasma neurotensin levels. Bile diversion produced a significant delay in this lag-phase of gastric emptying. These abnormalities in gut regulatory hormones appear to be adaptive changes to rapid early postprandial gastric emptying, probably related to antropyloric dysmotility, which has been implicated in the pathogenesis of this condition. Measurement of these gastrointestinal hormones may become useful in the diagnosis of primary DGR.

Is profound peripheral insulin resistance in patients with pancreatic cancer caused by a tumor-associated factor?

Diabetes in patients with pancreatic cancer occurs in 70% to 80% of the patients and is characterized by high plasma levels of insulin. In type II diabetes that is not associated with pancreatic cancer, peripheral insulin resistance and impaired muscle glycogen synthesis are major pathogenic factors. We investigated peripheral insulin sensitivity in patients with pancreatic cancer before and after tumor removal. The effects of pancreatic tumor extracts on glycogen synthesis in skeletal muscle in vitro and the tumor content of pancreatic islet hormones were also investigated. Marked peripheral insulin resistance was found in the patients with pancreatic cancer and was more pronounced in the diabetic patients than in the nondiabetic patients. Insulin sensitivity was not correlated with weight loss, tumor size, or bilirubin levels but improved after surgery. Tumor extracts from diabetic patients with pancreatic cancer caused a marked reduction of glycogen synthesis in skeletal muscle in vitro. All tumors contained islet hormones but not in concentrations sufficient to explain the effect on glycogen synthesis. These findings indicate that a diabetogenic factor associated with pancreatic adenocarcinomas could be involved in the development of the profound peripheral insulin resistance and thereby could contribute to the high incidence of diabetes observed in patients with pancreatic cancer.

The Development of a Functional Digestive System in the African Catfish Clarias gariepinus (Burchell)

AbstractThe morphological and physiological development of the intestine, stomach, liver and pancreas of the African catfish, Clarius guriepinus (Burchell 1822), was investigated from hatching until 9 days after the start of exogenous feeding by histological, histochemical and immunohistochemical procedures. During the yolk sac period, lasting 48 hours at 30 C, the digestive system develops from a rather undifferentiated system into a distinct liver and pancreas and a segmented intestine (parts I to III). Insulin and glucagon producing cells were clearly found in the endocrine pancreatic islets from 14 hours after hatching onwards, while at the start of exogenous feeding, the exocrine pancreas showed an intense zymogen colouration. Exogenous feeding started three days after fertilization, i.e., 48 hours after hatching. At that moment, the rearing temperature was lowered to 27.5 C. The first day of feeding was referred to as day zero, changing into day 1 when the first 24 hours of feeding were completed. From the start of exogenous feeding onwards, aminopeptidase, non‐specific esterase and ATP‐ase were detected in the digestive system. Morphologically, the stomach was completed at day 4 of exogenous feeding. Gastric acid secretion started on day 4 and lead to a pH below 3.3 in the stomach on day 5. During the first four days of exogenous feeding, C‐t‐gastrin immunopositive cells were found throughout the gut, including the gastric epithelium. After day 4, the C‐t‐gastrin cells were only detected in the anterior intestine. The completeness of the stomach development was also marked by the appearance of non‐specific esterase activity in the stomach epithelial cells on day 5. All data together clearly indicate that in Clarius gariepinus, the ontogeny of a functional digestive system has been completed on day 5 after the start of exogenous feeding, marking thereby the end of the larval period.

Characterization of the endocrine cells in the pancreatic-bile duct system of the rat.

Six types of endocrine cells showing immunolabelling against gut or pancreatic islet hormones were identified in the pancreatic-bile duct system of the normal adult rat at the light and electron microscopic levels. They were located within the epithelial lining of the duct system from the intercalated portion to its duodenal opening. However, the distribution and frequency of each endocrine cell varied along the length of the duct system. While insulin, glucagon, somatostatin, and pancreatic polypeptide cells were widely distributed along the entire duct system, small numbers of cholecystokinin and serotonin cells were confined to the terminal portion. A considerable number of somatostatin cells were concentrated in gland-like pouches of the terminal portion of the common pancreatic-bile duct. When the accessory pancreatic duct was present, insulin, glucagon, and somatostatin cells were also found in its epithelial lining. Electron microscopically, the specific content of the secretory granules of all endocrine cells was confirmed by immunolabelling or cytochemical staining. Further the characteristics of the secretory granules of each endocrine cell type corresponded to those present in the same kind of endocrine cells in gut or pancreatic islet. The duct endocrine cells displayed a particular ultrastructural appearance. The "open type cells" were highly polarized, with their apical cytoplasmic process reaching the duct lumen, whereas "closed type cells" showed long basal cytoplasmic processes with no connection with the duct lumen. In general, insulin, and somatostatin cells were of the "open type", while no morphological connection with the duct lumen was found for glucagon and pancreatic polypeptide cells. The presence of various duct endocrine cells with their particular ultrastructural appearance implies that they may take part in modulating the function of the duct system.

Interactions between Norepinephrine and Neuropeptide Y in Regulating Pancreatic Islet Hormone Secretiona

Interactions between Norepinephrine and Neuropeptide Y in Regulating Pancreatic Islet Hormone Secretiona

Islet amyloid polypeptide: Structure and upstream sequences of the IAPP gene in rat and man

Islet amyloid polypeptide (IAPP) or amylin is a pancreatic islet hormone which was first found in amyloid in insulinomas and in pancreases of patients with type 2 diabetes. In rat a similar polypeptide occurs; however, pancreatic amyloid in this species has not been described. Here we report the structure of the rat and human IAPP gene. Both consist of three exons and two introns which are very similar. The upstream sequence of the rat IAPP gene contains a TATA-box, a CCAAT-sequence and a GT-element, whereas the upstream sequence of the human IAPP gene contains a TATA-box and a rat insulin enhancer-like sequence. This suggests that the rat and human IAPP gene may be controlled differently at the transcriptional level.

Physiological and pharmacological stimulation of pancreatic islet hormone secretion in type I diabetic pancreas allograft recipients

Physiological and pharmacological stimulation of pancreatic islet hormone secretion in type I diabetic pancreas allograft recipients

Physiological and Pharmacological Stimulation of Pancreatic Islet Hormone Secretion in Type I Diabetic Pancreas Allograft Recipients

Successful heterotopic and denervated pancreas allograft transplantation (PAT) often results in normoglycemia and peripheral hyperinsulinemia in insulin-dependent (type I) diabetic recipients. The contribution of altered hepatic insulin extraction (HIE) to the resulting hyperinsulinemia in such patients remains uncertain. Furthermore, whether the denervated pancreas allografts exhibit beta-cell hyperresponsiveness to physiological and pharmacological stimulation is controversial. We evaluated beta-cell function and HIE after successful whole cadaveric PAT with systemic venous drainage in 13 type I diabetic patients before and after mixed-meal and intravenous glucose and glucagon administration. The results were compared with those of 5 nondiabetic patients with kidney transplantation only, who had native innervated pancreases with portal insulin delivery and were receiving an equivalent triple immunosuppressive therapy (cyclosporin, azathioprine, and prednisone), and 7 healthy control subjects with no family history of diabetes. After PAT, fasting and poststimulation serum glucose concentrations were normalized. PAT was associated with marked basal hyperinsulinemia (3- to 8-fold) as assessed by immunoreactive insulin (IRI) levels in type I diabetic patients (mean +/- SE 345 +/- 43 pM) compared with control subjects (43 +/- 14 pM) and nondiabetic kidney-transplantation patients (129 +/- 38 pM). After mixed-meal ingestion, the mean incremental integrated insulin area was similar in PAT patients (18 +/- 3 nM.min) compared with kidney-transplantation patients (20 +/- 4 nM.min) and healthy control subjects (21 +/- 3 nM.min). Basal serum C-peptide levels were significantly greater in PAT (1.72 +/- 0.13 nM) and kidney-transplantation (2.15 +/- 0.33 nM) patients than in healthy control subjects (0.50 +/- 0.10 nM; P less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Islet amyloid polypeptide (IAPP) does not inhibit glucose-stimulated insulin secretion from isolated perfused rat pancreas

Islet amyloid polypeptide (IAPP) is a recently discovered pancreatic islet hormone which is stored with insulin in the secretory vesicles of beta cells. Several lines of evidence suggested that IAPP might affect glucose-stimulated insulin secretion and, therefore, might play a role in the development of impaired insulin secretion which is typical of type 2 diabetes. In this study, the effects of human IAPP (amide) on glucose-stimulated insulin secretion was evaluated in the isolated perfused rat pancreas. IAPP in concetrations from 5 × 10 −12 to 10 −7 M had no significant effects on insulin secretion. IAPP, therefore, does not appear to be a significant modulator of glucose-stimulated insulin secretion at concentrations that are physiologically relevant.

Canine IAPP cDNA sequence provides important clues regarding diabetogenesis and amyloidogenesis in type 2 diabetes

Islet amyloid polypeptide (IAPP) is a recently discovered pancreatic islet hormone which is stored with insulin in beta cell granules. IAPP may have a significant role in the development of Type 2 diabetes mellitus due to its propensity to form islet cell-disrupting amyloid deposits, and by opposing the action of insulin in peripheral tissues. Most evidence to-date suggests that an intrinsic structural motif of IAPP is linked to the amyloidogenicity of IAPP, and that this motif occurs only in those species (e.g., humans and cats) that also develop age-associated or Type 2 diabetes. We utilized polymerase chain reaction methodology in this study to obtain the IAPP nucleotide and protein sequences of the dog, a species not known to develop islet amyloid. We show that dog IAPP contains the same putative amyloidogenic sequence (GAILS) at residues 24–28 as human and cat IAPP, and that although dogs do not develop islet amyloid they do develop IAPP-derived amyloid in association with neoplastic beta cells (i.e., insulinomas). These results provide strong evidence that the amyloidogenicity of IAPP is linked to at least two prerequisites: a species-specific amyloidogenic structural motif, and aberrations in the synthesis (or processing) of IAPP which leads to increased concentration of IAPP in the local milieau.

Islet Amyloid Polypeptide and Calcitonin Gene-related Peptide Immunoreactivity in Amyloid and Tumor Cells of Canine Pancreatic Endocrine Tumors

Seven canine pancreatic endocrine tumors were evaluated immunohistochemically for the presence of islet amyloid polypeptide (IAPP), calcitonin gene-related peptide (CGRP), and several other pancreatic hormones. Four tumors contained cells with IAPP immunoreactivity, and four had cells with CGRP immunoreactivity. IAPP and CGRP immunoreactivities were localized to distinctly different cell populations in three tumors in which both peptides were detected; however, IAPP immunoreactivity consistently was found in cells that also contained insulin immunoreactivity. Amyloid deposits, which were found in three of the seven tumors, showed strong immunoreactivity with antiserum against IAPP and weaker immunoreactivity with antiserum to CGRP. These results indicate that amyloid deposits in canine pancreatic endocrine tumors are likely derived from IAPP, as is amyloid found in human pancreatic endocrine tumors and pancreatic islet amyloid in aged and diabetic persons and cats.

Promoting effect of bombesin on the cell proliferation in the rat endocrine pancreas during the early postnatal period

The present work investigated whether orally administered bombesin influences cell proliferation in the endocrine pancreatic islets of rats during the suckling period and after weaning. Four series of pups were given bombesin diluted in milk (20 μg/kg, 3 times daily) or milk alone for 5 days during either the first, second, third or fourth postnatal week of life. Oral administration was used because bombesin-like peptides have been identified in the breast milk of mammals. 45 min before death, animals were given a single [ 3H]thymidine pulse injection. Tissue sections were processed for radioautography; DNA labeling and mitotic indices were estimated after counting at least 1000 endocrine cells per rat pancreas. In control rats, the labeling and mitotic indices in pancreatic islets dropped regularly from the first week to the fourth week of life (3.6% ± 0.2% versus 1.9% ± 0.1% and 0.46% ± 0.09% versus 0.08% ± 0.02%, respectively). Orogastric bombesin administration significantly increased the DNA labeling and mitotic indices at the end of the first week (+20% and +62%, respectively) and second week of life (+37.5% and +49%, respectively) ( P < 0.05 to P < 0.005), but did not modify these parameters for the third and subsequent weeks of life. Therefore, this study provides evidence that bombesin stimulates DNA synthesis and cell division in pancreatic endocrine cells during the developmental period.

Developmental Patterns for Pancreatic Opioids in the Rat

Developmental patterns for rat pancreatic opioid peptides and islet hormones were studied from gestational day 20 through adulthood. Fetal tissue was obtained as well as pancreas at birth (day 0), and postnatal days 3, 7, 14, and 21, and 7 weeks. The hormones measured included insulin, glucagon, and somatostatin. The opioids measured were beta-endorphin, Met- and Leu-enkephalins, and the high molecular weight enkephalin precursors. Pancreata were pooled as necessary and extracted (acid alcohol, or hot acetic acid), and opioids were further purified on reversed-phase C-18 (Sep-pak) cartridges. In all instances measurements were made by radioimmunoassays. Precursor peptides were first digested (with trypsin and carboxypeptidase B) prior to immunoassay. All opioids and hormones except the precursors for enkephalins showed a well-defined surge in pancreatic concentration during the first postnatal week. In contrast, the precursors had the highest concentration in the fetus, and by the seventh day of life had decreased by greater than 50%. This progressive decrease may represent maturation of the enkephalin convertase and trypsin-like enzymes in the islets. The opioid and hormonal surges that we have described are similar to the surge in islet concentration of thyroid-releasing hormone (TRH) previously described in neonatal rat islets. It is suggested that these postnatal alterations in opioid and hormone concentration relate to a specific function in the development of the endocrine pancreas.

The parathyroid hormone-like peptide gene is expressed in the normal and neoplastic human endocrine pancreas.

PTH-like peptide (PLP) is produced by a number of tumors commonly associated with the development of hypercalcemia. Analysis of the expression of the PLP gene has demonstrated that a variety of non-neoplastic endocrine and nonendocrine tissues contain PLP mRNA transcripts. Using a combination of Northern blot analysis, immunohistochemistry, and RIAs, we have demonstrated that the PLP gene is expressed in normal human and rat fetal and adult islets of Langerhans. PLP gene expression was not confined to cells containing a single pancreatic islet hormone, but was found in cells of all four major endocrine subtypes. PLP mRNA transcripts were also detected in RNA prepared from isolated rat islets, and small amounts of PLP immunoreactivity were secreted by cultured rat islets. Fifteen human pancreatic endocrine tumors not associated with hypercalcemia were analyzed and PLP-immunopositive tumor cells were found in 13. These observations demonstrate that the PLP gene is expressed in the normal and neoplastic islets of Langerhans, and suggests a possible role for this peptide in the growth or function of the endocrine pancreas.