Periphery Of Islets Research Articles

Localization of TRAIL/TRAILR in fetal pancreas.

To observe the localization of TRAIL/TRAIR (DR4, DR5, DcR1, DcR2) in the fetal pancreas. Fetal pancreas of 32 weeks of pregnancy were obtained from induced abortions, embedded in paraffin, and 4-microm sections were prepared. The localization of TRAIL/TRAILR in fetal pancreas was investigated by fluorescence immunohistochemical method combined with laser scanning confocal microscopy. TRAIL immunoreactive cells were mainly located on the periphery of the pancreas islets. There were a few DcR1 and DcR2 positive cells whereas there were no immunoreactive cells of DR4 and DR5 in the pancreas islets. In the acini and the ducts of the exocrine pancreas there were no TRAIL/TRAILR immunoreactive cells. This study not only describes the distribution of TRAIL/TRAILR in the fetal pancreas, but also provides a morphological basis for deducing the function of TRAIL/TRAILR in pancreas, suggesting that in normal pancreatic islets, the pancreatic cells are resistant towards apoptosis too.

Blockade of IRS1 in isolated rat pancreatic islets improves glucose-induced insulin secretion

Several neural, hormonal and biochemical inputs actively participate in the balance of insulin secretion induced by blood glucose fluctuations. The exact role of insulin as an autocrine and paracrine participant in the control of its own secretion remains to be determined, mostly due to insufficient knowledge about the molecular phenomena that govern insulin signaling in pancreatic islets. In the present experiments we demonstrate that higher insulin receptor and insulin receptor substrates-1 and -2 (IRS1 and IRS2) concentrations are predominantly encountered in cells of the periphery of rat pancreatic islets, as compared to centrally located cells, and that partial blockade of IRS1 protein expression by antisense oligonucleotide treatment leads to improved insulin secretion induced by glucose overload, which is accompanied by lower steady-state glucagon secretion and blunted glucose-induced glucagon fall. These data reinforce the inhibitory role of insulin upon its own secretion in isolated, undisrupted pancreatic islets.

Neuropilin-2 is a novel marker expressed in pancreatic islet cells and endocrine pancreatic tumours.

Neuropilin-2 (NP-2) is a cell surface transmembrane protein originally characterized as a receptor for the type 3 semaphorins, and more recently for a number of vascular endothelial growth factor (VEGF) isoforms. NP-2 expression has been recently localized to a subset of neuroendocrine cells in the gastrointestinal tract. The aim of this study was to define the expression pattern of NP-2 in normal pancreatic islets and to determine the utility of NP-2 expression as a diagnostic marker of pancreatic endocrine tumours. Paraffin-embedded tissue sections from 30 endocrine pancreatic tumours (EPTs) and from normal pancreas were immunostained with a rabbit polyclonal antibody generated towards NP-2. Nineteen of the tumours were hormonally functional (nine insulinomas, nine gastrinomas, and one glucagonoma). The NP-2 staining pattern was correlated with islet cell hormone expression. In addition, NP-2 expression was evaluated in other normal neuroendocrine tissues and neuroendocrine neoplasms. In normal pancreas, NP-2 stained a distinct subset of islet cells situated primarily at the islet periphery. Double immunohistochemical staining revealed co-localization with glucagon-expressing cells. Moderate to strong NP-2 staining was present in 27 of 30 EPTs. Serial staining of the pancreatic tumours with insulin, gastrin, glucagon, pancreatic polypeptide (PP) or somatostatin did not reveal a distinct pattern of co-localization. NP-2 expression was not detected in neuroendocrine cells outside the gastroenteropancreatic system, or in their corresponding neoplasms, except for focal staining in one bronchial carcinoid tumour. In conclusion, the vast majority of EPTs examined expressed NP-2, suggesting its utility as a diagnostic marker for these tumours. The function of NP-2 in islet cell biology or tumourigenesis remains to be elucidated.

The ghrelin cell: a novel developmentally regulated islet cell in the human pancreas.

Ghrelin, an endogenous ligand of the growth hormone secretagogue receptor (GHS-R), was recently identified in the stomach. Ghrelin is produced in a population of endocrine cells in the gastric mucosa, but expression in intestine, hypothalamus and testis has also been reported. Recent data indicate that ghrelin affects insulin secretion and plays a direct role in metabolic regulation and energy balance. On the basis of these findings, we decided to examine whether ghrelin is expressed in human pancreas. Specimens from fetal to adult human pancreas and stomach were studied by immunocytochemistry, for ghrelin and islet hormones, and in situ hybridisation, for ghrelin mRNA. We identified ghrelin expression in a separate population of islet cells in human fetal, neonatal, and adult pancreas. Pancreatic ghrelin cells were numerous from midgestation to early postnatally (10% of all endocrine cells). The cells were few, but regularly seen in adults as single cells at the islet periphery, in exocrine tissue, in ducts, and in pancreatic ganglia. Ghrelin cells did not express any of the known islet hormones. In fetuses, at midgestation, ghrelin cells in the pancreas clearly outnumbered those in the stomach. Ghrelin is expressed in a quite prominent endocrine cell population in human fetal pancreas, and ghrelin expression in the pancreas precedes by far that in the stomach. Pancreatic ghrelin cells remain in adult islets at lower numbers. Ghrelin is not co-expressed with any known islet hormone, and the ghrelin cells may therefore constitute a new islet cell type.

Transgenic Expression of FGF8 and FGF10 Induces Transdifferentiation of Pancreatic Islet Cells into Hepatocytes and Exocrine Cells

FGF signaling is essential for normal development of pancreatic islets. To examine the effects of overexpressed FGF8 and FGF10 on pancreatic development, we generated FGF8- and FGF10-transgenic mice (Tg mice) under the control of the glucagon promoter. In FGF8-Tg mice, hepatocyte-like cells were observed in the periphery of pancreatic islets, but areas of α and β cells did not decrease, whereas in FGF10-Tg mice, pancreatic ductal and acinar cells were found in islets, concomitantly with disturbed β-cell differentiation. These results suggest that FGF8 and FGF10 play important roles in development of hepatocytes and exocrine cells, respectively, and explain the absence of FGF8 expression in normal islets and pancreatic hypoplasia in FGF10-deficient mice.

Ghrelin is present in pancreatic alpha-cells of humans and rats and stimulates insulin secretion.

Ghrelin, a novel growth hormone-releasing peptide isolated from human and rat stomach, is a 28-amino acid peptide with a posttranslational acylation modification that is indispensable for stimulating growth hormone secretion by increasing intracellular Ca(2+) concentration. It also functions in the regulation of feeding behavior, energy metabolism, and gastric acid secretion and motility. Using two different antibodies against the NH(2)- and COOH-terminal regions of ghrelin, we studied its localization in human and rat pancreas by immunohistochemistry. Ghrelin-immunoreactive cells were identified at the periphery of pancreatic islets in both species. Ghrelin co-localized exclusively with glucagon in rat islets, indicating that it is produced in alpha-cells. We identified ghrelin and des-acyl ghrelin in the rat pancreas using reverse-phase high-performance liquid chromatography combined with two radioimmunoassays. We also detected mRNA encoding ghrelin and its receptor in the rat pancreatic islets. Ghrelin increased the cytosolic free Ca(2+) concentration in beta-cells and stimulated insulin secretion when it was added to isolated rat pancreatic islets. These findings indicate that ghrelin may regulate islet function in an endocrine and/or paracrine manner.

An osmotic-sensitive taurine pool is localized in rat pancreatic islet cells containing glucagon and somatostatin.

Previous reports have dealt with the hypoglycemic properties of taurine and its effects on insulin secretion by adult and fetal isolated islets. We have studied the presence and cellular distribution of taurine in rat islets, the conditions to evoke its release, and its possible modulatory action on insulin secretion. We localized taurine by techniques of double immunolabeling in most glucagon-positive cells and in some somatostatin-positive cells, whereas insulin-positive cells were not labeled with the taurine antibody. Although high-glucose stimulation did not evoke any taurine release, a hyposmotic solution (17% osmolarity reduction) induced a specific phasic release of taurine and GABA (34 and 52% increase on their basal release rate). On the other hand, taurine (10 mmol/l) application slightly reduced the second phase of insulin secretion induced by glucose stimulation. In conclusion, taurine is highly concentrated in glucagon-containing cells of the islet periphery. It is not liberated by glucose stimulation but is strongly released under hyposmotic conditions. All of these data suggest that taurine plays an osmoregulatory role in alpha-cells.

Is pancreas development abnormal in the non-obese diabetic mouse, a spontaneous model of type I diabetes?

Despite extensive genetic and immunological research, the complex etiology and pathogenesis of type I diabetes remains unresolved. During the last few years, our attention has been focused on factors such as abnormalities of islet function and/or microenvironment, that could interact with immune partners in the spontaneous model of the disease, the non-obese diabetic (NOD) mouse. Intriguingly, the first anomalies that we noted in NOD mice, compared to control strains, are already present at birth and consist of 1) higher numbers of paradoxically hyperactive beta cells, assessed by in situ preproinsulin II expression; 2) high percentages of immature islets, representing islet neogenesis related to neonatal beta-cell hyperactivity and suggestive of in utero beta-cell stimulation; 3) elevated levels of some types of antigen-presenting cells and FasL+ cells, and 4) abnormalities of extracellular matrix (ECM) protein expression. However, the colocalization in all control mouse strains studied of fibroblast-like cells (anti-TR-7 labeling), some ECM proteins (particularly, fibronectin and collagen I), antigen-presenting cells and a few FasL+ cells at the periphery of islets undergoing neogenesis suggests that remodeling phenomena that normally take place during postnatal pancreas development could be disturbed in NOD mice. These data show that from birth onwards there is an intricate relationship between endocrine and immune events in the NOD mouse. They also suggest that tissue-specific autoimmune reactions could arise from developmental phenomena taking place during fetal life in which ECM-immune cell interaction(s) may play a key role.

Roles of ATP-sensitive K+ channels in cell survival and differentiation in the endocrine pancreas.

To determine the roles of the ATP-sensitive K+ (K(ATP)) channels in endocrine pancreas more directly, two types of genetically engineered Kir6.2 mice were developed: mice expressing a dominant-negative form of Kir6.2 specifically in beta-cells (Kir6.2G132S Tg mice) and mice lacking Kir6.2 (Kir6.2-/- or Kir6.2 null mice). The Kir6.2G132S Tg mice show severe impairment of K(ATP) channel function only in the beta-cells, whereas Kir6.2 null mice are completely defective in K(ATP) channel function in all of the cells in which Kir6.2 is a constituent of the K(ATP) channels, because of the disruption of Kir6.2. Both types of mice show abnormal architecture of the pancreatic islets. The number of beta-cells in Kir6.2G132S Tg mice decreases markedly with age, whereas that in Kir6.2-/- mice decreases slightly. alpha-Cells, which are normally present only in the periphery of pancreatic islets, also appear in the center of the islets in both Kir6.2G132S Tg and Kir6.2-/- mice. Interestingly, the number of peptide YY (PYY) and glucagon-positive cells is markedly increased in Kir6.2 null mice, whereas the number of PP cells and delta-cells is not altered. Apoptotic cells are detected by the TdT-mediated dUTP nick-end labeling (TUNEL) method at a high frequency in both Kir6.2G372S Tg and Kir6.2-/- mice compared with the respective controls. Thus, studies of Kir6.2G372S Tg and Kir6.2-/- mice indicate that K(ATP) channels play an important role in cell survival and differentiation in the endocrine pancreas.

Site-Specific Localization of Protein Kinase C Isoforms in Rat Pancreas

Background: Protein kinase C (PKC), a major signal-transducing enzyme, is recognized to play an important role in the regulation of pancreatic exocrine and endocrine secretion, and yet the distribution of PKC isoforms in rat pancreas has remained unclarified. Aim of the Study: We examined the precise localization of PKC isoforms to elucidate the role of PKC in the normal rat pancreas. Methods: Male Sprague-Dawley rats were used throughout the experiment. For Western blot analysis, the islet of Langerhans and the acinar tissue were separated by the collagenase digestion method. Also, the whole pancreas was taken out and immunohistochemistry performed. Results: According to Western blot analysis, PKC-α, -γ, -δ, -Ε, -ς, and -λ were detected in both acinar and islet cells while PKC-βII were observed exclusively in the islet. PKC-βI was not observed. On immunohistochemistry, the immunoreactivities of PKC isoforms were observed as follows: PKC-α, weakly in some endocrine cells and ductal epithelium; PKC-βII, mainly in the islet center; PKC-γ, in the islet, intrapancreatic ganglia and ductal epithelium; PKC-δ, in the islet periphery, weakly in some acinar cells and ductal epithelium; PKC-Ε, strongly in the islet, acinar cell and ductal epithelium; PKC-ς, in the islet, acinar cell and ductal epithelium; PKC-λ in some endocrine cells and ductal epithelium. Conclusion: These results suggest that the intrapancreatic site-specific existence of PKC isoforms may regulate pancreatic exocrine and endocrine functions via a PKC-mediated signal transduction.

Hydrolysed Casein Diet Protects BB Rats from Developing Diabetes by Promoting Islet Neogenesis

Feeding diabetes-prone BioBreeding (BBdp) rats a hydrolysed-casein (HC)-based semi-purified diet results in two-to-three-fold fewer diabetes cases compared with feeding cereal-based diets such as NIH-07 (NIH). We showed previously that young NIH-fed BBdp rats had decreased islet area at a time when classic insulitis was minimal. Rats fed an HC diet maintained near normal islet area followed 3–4 weeks later by a deviation of the pancreas cytokine pattern from Th1 to Th2/Th3. This finding raised the possibility that BBdp rats were more susceptible to diet-induced changes in islet homeostasis. To investigate this possibility further, BBdp rats were fed an NIH or HC diet from days 23 to 45. Bouin's fixed sections of pancreas were stained with H&E or antibodies for insulin and glucagon. Cell proliferation nuclear antigen (PCNA) was used as a marker of cell proliferation and cells were stained for putative markers of islet neogenesis, cytokeratin 20 (CK20) and Bcl-2. Apoptotic bodies were recognized by morphological features and by TUNEL-positive staining. BBdp rats fed an HC diet had a significantly higher β-cell fraction than rats fed NIH, whereas α-cell fraction and β-cell size were not affected by diet or rat type. Apoptotic bodies of β-cells were rare and unaffected by diet. The number of PCNA+β-cells was not affected by diet. CK20 expression was localized in the ductular system and at the periphery of islets in rats aged 7 and 45 days. There were more CK20+islets in BBdp rats fed NIH than in those fed HC but the CK20 area fraction was unaffected by diet. Bcl-2 expression was scattered among ducts and central acinar cells. The number of extra-islet insulin+and glucagon+clusters (<four cells) was significantly higher in animals fed the HC diet compared with those fed NIH. Most of the insulin+clusters were also homeodomain-containing transcription factor pancreas duodenum homeobox gene-1 (PDX-1) positive. Glucagon+/PDX-1+clusters were rarely found. These data are consistent with a shift in pancreas homeostasis that maintains islet cell mass by increased islet neogenesis, a process that was enhanced in animals fed a diabetes-retardant diet.

Possible relationship between changes in islet neogenesis and islet neogenesis-associated protein-positive cell mass induced by sucrose administration to normal hamsters.

The possible relationship between changes in islet cell mass and in islet neogenesis-associated protein (INGAP)-cell mass induced by sucrose administration to normal hamsters was investigated. Normal hamsters were given sucrose (10% in drinking water) for 5 (S8) or 21 (S24) weeks and compared with control (C) fed hamsters. Serum glucose and insulin levels were measured and quantitative immunocytochemistry of the endocrine pancreas was performed. Serum glucose levels were comparable among the groups, while insulin levels were higher in S hamsters. There was a significant increase in beta-cell mass (P<0.02) and in beta-cell 5-bromo-2'-deoxyuridine index (P<0.01), and a significant decrease in islet volume (P<0.01) only in S8 vs C8 hamsters. Cytokeratin (CK)-labelled cells were detected only in S8 hamsters. INGAP-positive cell mass was significantly larger only in S8 vs C8 hamsters. Endocrine INGAP-positive cells were located at the islet periphery ( approximately 96%), spread within the exocrine pancreas ( approximately 3%), and in ductal cells (<1%) in all groups. INGAP positivity and glucagon co-localization varied according to topographic location and type of treatment. In C8 hamsters, 49.1+/-6. 9% cells were INGAP- and glucagon-positive in the islets, while this percentage decreased by almost half in endocrine extra-insular and ductal cells. In S8 animals, co-expression increased in endocrine extra-insular cells to 36.3+/-9.5%, with similar figures in the islets, decreasing to 19.7+/-6.9% in ductal cells. INGAP-positive cells located at the islet periphery also co-expressed CK. In conclusion, a significant increase of INGAP-positive cell mass was only observed at 8 weeks when neogenesis was present, suggesting that this peptide might participate in the control of islet neogenesis. Thus, INGAP could be a potentially useful tool to treat conditions in which there is a decrease in beta-cell mass.

Peptidergic hormones and neuropeptides, and aminergic neurotransmitters of the pancreatic islets of the Houbara bustard (Chlamydotis undulata).

Immunoreactivity to insulin (Ins), somatostatin (Som), glucagon (Glu) and pancreatic polypeptide (PP) was found in 70%, 22%, 15% and 11% respectively of Houbara pancreatic endocrine islet cells. Whilst Ins occurred centrally and SOM was observed both in peripherally and centrally located islets, the other hormones were localised in peripheral islet cells; Som was also observed in neuronal cell bodies and nerve fibres. In addition, the islet cells contained substance P (SP) (65%) in the centre and vasoactive intestinal polypeptide (VIP) (2%) at the periphery. Immunoreactivity to choline acetyltransferase (ChAT), VIP and galanin (Gal) occurred in the walls of blood vessels located mainly at the periphery of islets. Occasionally, VIP and Gal immunoreactive varicose nerve terminals and ChAT immunoreactive cell bodies were also observed in the centre of islets. SP neuronal cell bodies were not observed but prominent SP immunoreactive varicose terminals were discernible in capillary walls within the islets. Neuropeptide Y (NPY) immunoreactive neurons were detected in neuronal cell bodies located mainly peripherally. Neuronal nitric oxide synthase (nNOS) immunoreactivity occurred in neuronal cell bodies and nerve fibres mainly at the periphery and also in centrally located islet endocrine cells. Immunoreactivity to tyrosine hydroxylase (TH) was similar in distribution to that of ChAT. In comparison with other avian species, the islets of the dorsal pancreatic lobe of the bustard contain all the peptidergic hormones normally present in the islets of other avian species, but are not segregated into dark A and light B cells. Many of the insulin containing cells also contained SP. The islets also contained several neuropeptides which are probably involved in their regulation.

Induction of resistance to diabetes in non-obese diabetic mice by targeting CD44 with a specific monoclonal antibody.

Inflammatory destruction of insulin-producing beta cells in the pancreatic islets is the hallmark of insulin-dependent diabetes mellitus, a spontaneous autoimmune disease of non-obese diabetic mice resembling human juvenile (type I) diabetes. Histochemical analysis of diabetic pancreata revealed that mononuclear cells infiltrating the islets and causing autoimmune insulitis, as well as local islet cells, express the CD44 receptor; hyaluronic acid, the principal ligand of CD44, is detected in the islet periphery and islet endothelium. Injection of anti-CD44 mAb 1 hr before cell transfer of diabetogenic splenocytes and subsequently on alternate days for 4 weeks induced considerable resistance to diabetes in recipient mice, reflected by reduced insulitis. Contact sensitivity to oxazolone was not influenced by this treatment. A similar antidiabetic effect was observed even when the anti-CD44 mAb administration was initiated at the time of disease onset: i.e., 4-7 weeks after cell transfer. Administration of the enzyme hyaluronidase also induced appreciable resistance to insulin-dependent diabetes mellitus, suggesting that the CD44-hyaluronic acid interaction is involved in the development of the disease. These findings demonstrate that CD44-positive inflammatory cells may be a potential therapeutic target in insulin-dependent diabetes.

Localization of monoamine oxidase A and B in human pancreas, thyroid, and adrenal glands.

We studied monoamine oxidase (MAO) A and B localization in human pancreas, thyroid gland, and adrenal gland by immunohistochemistry. The primary antibodies used were mouse monoclonal anti-human MAO-A (6G11/E1) and anti-human MAO-B (3F12/G10/2E3). Samples were obtained from six routine autopsy cases and fixed in 2% paraformaldehyde. Exocrine pancreas showed a widespread distribution of MAO-A, whereas MAO-B was present only in centroacinar cells and epithelial cells of pancreatic ducts. In endocrine pancreas, MAO-A was observed in around 50% of islet cells, whereas MAO-B was less abundant and was restricted to the periphery of islets. Thyroid gland showed strong MAO-A immunoreactivity in all cell types and was MAO-B-negative. In adrenal gland, the capsule displayed MAO-A but not MAO-B immunoreactivity, whereas the cortex showed widespread MAO-A staining but was MAO-B-negative in interstitial cells. Finally, in the medulla only a few scattered cells showed either MAO-A or MAO-B immunoreactivity. To our knowledge, these data represent the first study of the cellular distribution of MAO-A and MAO-B in the three human tissues included.

Ultrastructure and Immunocytochemistry of the Islet Organ of Osteoglossomorpha (Teleostei)

Both routine electron microscopy and immunocytochemistry with protein A–gold were used to identify the cell types within the islet organs of four species of teleosts (Osteoglossum bicirrhosum, Pantodon buchholzi, Notopterus chitala, and Gnathonemus petersii) within Osteoglossomorpha, a subdivision with an ancient lineage. Four primary endocrine cell types, A, B, D, and F, were identified within the islets of the four species examined. The B- and D-cells were located mainly in the central core of the islet in the four species. In general, the A-cells were located at the islet periphery in all of the four species but in P. buchholzi and N. chitala they were also differently distributed toward the islet core. F-cells were present only at the islet periphery. Granules of B-cells in three species had a relatively homogeneous shape of the matrix core, but in O. bicirrhosum, the shape varied greatly. Variation in matrix shape of B-cell granules may indicate a different conformation of insulin molecules among at least some species of osteoglossomorphs, and this observation may have some taxonomic significance. Two somatostatin-containing (SST) D-cell types (D1 and DX) with granules of different shape were observed in all four species of osteoglossomorphs. The granules of the two D-cells immunostained either with anti-SST-25 and anti-SST-14 (D1-cells) or with anti-SST-34 (DX-cells). Immunocytochemistry confirmed that A-cells, containing glucagon-family peptides, and F-cells, containing peptides of the pancreatic polypeptide family, had granules of different shape. The cells of the islet organs of these osteoglossomorphs are more similar to those in more derived teleosts than they are to those of nonteleost actinopterygians.

The structural integrity of the islet in vitro: the effect of incubation temperature.

The purpose of this study was to examine the effect of incubation temperature on the structural integrity of the islet during culture. Islets were isolated from the pancreas of the Syrian golden hamster and cultured in a collagen gel for < or =12 days at 24 degrees C or 37 degrees C. At 24 degrees C, cells in the islet periphery died, leading to a complete disintegration of the mantle region in 37.4+/-5.6% of the islets. In comparison, at 37 degrees C, few islets exhibited mantle disintegration (p<0.001). Insulin immunoreactivity was distributed nonhomogeneously in islets at 24 degrees C, and the intensity of the staining, by using a semiquantitative scale (0-3), was +1. Islets cultured at 37 degrees C had a normal homogeneous distribution of insulin immunoreactivity with a score of +3. As the pancreas is a complex gland composed of different cell types, and cell-cell interactions are known to be important in the maintenance of cell survival, additional experiments were repeated to include the coculture of islets with duct epithelial cells. The proportion of islets that developed mantle disintegration was now reduced to 2.5+/-0.3% (p<0.001), comparable to that seen at 37 degrees C. Similar results were obtained for islets cultured in the presence of duct-conditioned medium (DCM). Together with the preservation of the islet mantle, islets cultured in the presence of duct epithelial cells or DCM had a normal homogeneous distribution of insulin immunoreactivity, with a staining intensity of +3. We conclude that incubation temperature has a profound effect on the structural integrity of islets, and that the detrimental effects of low-temperature culture can be mitigated by coculture of islets with secretory products derived from pancreatic ductal cells. These data provide evidence for a trophic relation between pancreatic islets and ductal epithelium.

One thousand faces of Langerhans islets.

Studies with different strains of Syrian hamsters and Syrian golden hamsters have revealed the remarkable potential of islet cells to undergo orthotopic and heterotopic metaplasia. The most common spontaneous change included the development of hepatocytes in aged and malnourished hamsters. Of the many other alterations that occurred during carcinogenesis, most of the metaplastic changes originated within the islet periphery and progressed inside and outside the islets. The development of ductular structures within islets and their progression either to structures identical to human serous cystadenoma or to highly invasive adenocarcinomas were the most common alterations. The remarkably greater invasive potential of cancer cells arising within the islets contrasted sharply with the slow growth of the tumors developing within ducts (intraductal tumors). Studies in human tissue also showed development of malignant cells within islets, and, in some cases, transition of islet cells to malignant cells was suggested. The overall results, along with recent findings in other studies in cultured human and hamster islets, indicate the enormous potential of islet cells to differentiate and undergo malignant transformation. Whether the metaplastic and malignant cells derive from stem cells embedded within islets or from transdifferentiated islet cells remains to be seen.

Long-term survival, morphology and in vitro function of isolated pig islets under different culture conditions.

Islet culture aims to optimize islet survival and to reduce islet immunogenicity. To achieve these objectives, culture periods at 37 degrees C and 22-24 degrees C are mainly used. This study compares the influence of donor age (juvenile vs. adult), temperature (22 degrees C vs. 37 degrees C), and serum supplementation (10% newborn calf serum [NCS] with 10% pig serum) on morphological integrity and in vitro function of porcine islets during long-term culture (LTC). After 21 days at 22 degrees C, the survival rate of cultured islets isolated from juvenile donors was lower than of adult islets (23+/-0.9% vs. 88+/-2.8%, P<0.001). Compared with 37 degrees C, LTC at 22 degrees C increased survival of adult islets and DNA recovery (92+/-2.5% vs. 45+/-4.8%, P<0.001; 72+/-4.1% vs. 30+/-5.1%, P<0.001) and reduced viability (62+/-8% vs. 89+/-5%, P<0.05). LTC at 22 degrees C was associated with a reduction of insulin content (85+/-9 vs. 152+/-10 microU/islet equivalents [IEQ], P<0.01), 24 hr-insulin secretion (82+/-7 vs. 552+/-91 microU/ day/IEQ, P<0.001), and integrated dynamic insulin response to glucose (1093+/-124 vs. 3074+/-708 microU/60 min/100 IEQ, P<0.05), compared with 37 degrees C LTC. Histologic analysis revealed disintegration of islet periphery after 22 degrees C, whereas smoothly shaped islets were present after 37 degrees C LTC. Integrity after 14 days at 37 degrees C was significantly better preserved when medium CMRL 1066 was supplemented with 10% porcine serum, compared with 10% NCS (40+/-2.3% vs. 21+/-6.7%, P<0.05), contrasting with 22 degrees C (52+/-4.0% vs. 59+/-3.7%, not significant). This study demonstrates that survival of cultured porcine islets is increased at 22 degrees C, whereas in vitro function and viability are better preserved at 37 degrees C. Survival at 37 degrees C can be improved by adding homologous serum to the medium.

Interaction of islet hormones with cholecystokinin octapeptide-evoked secretory responses in the isolated pancreas of normal and diabetic rats.

This study investigates the effects of the islet hormones, insulin (Ins), glucagon (Glu) and somatostatin (Som) with cholecystokinin octapeptide (CCK-8) on amylase secretion and intracellular free calcium concentration [Ca2+]i and their pattern of distribution in the isolated pancreas of normal and diabetic rats. Ins and Glu evoked small increases in amylase output from pancreatic segments compared with a much enhanced effect of CCK-8. In contrast, Som induced a biphasic response comprising an initial decrease followed by a secondary increase and this biphasic response may be dependent upon the concentration. Combining the islet hormones with CCK-8 resulted in marked potentiation in amylase output compared with either CCK-8 alone or the individual hormone. Genistein and tyrphostin A25, the tyrosine kinase inhibitors, evoked a small decrease in amylase output from pancreatic segments. They had no effect on the CCK-8-evoked secretory response but markedly inhibited the potentiation of the islet hormones with CCK-8. In pancreatic acini and acinar cells Ins, Glu and Som individually evoked small increases in amylase output compared with a much larger response with CCK-8. When the islet hormones were combined with CCK-8 there was no potentiation of amylase output. Similarly, when rats were rendered diabetic by prior treatment with streptozotocin Ins, Glu and Som failed to potentiate the secretory response of CCK-8. In fura-2-loaded pancreatic acinar cells Ins or Glu evoked small increases in [Ca2+]i compared with a much larger elevation with CCK-8. Ins, Glu and Som each enhanced the CCK-8-evoked [Ca2+]i. Genistein elicited a decrease in [Ca2+]i both in the absence and presence of the islet hormones. It also decreased the elevation in [Ca2+]i resulting from the combined presence of CCK-8 with either Ins or Glu but it had no effect on CCK-8 in combination with Som. In pancreatic acinar cells from diabetic rat Ins, Glu and Som had no detectable effect on CCK-8-evoked elevation in [Ca2+]i compared with the response obtained with CCK-8 alone. CCK-8-immunopositive cells were distributed around the walls of blood vessels, numerous Ins-positive cells in the central and peripheral parts of the islets of Langerhans, Glu-immunoreactive cells in the periphery of islets and Som-positive cells in the outer part of the islets. During diabetes, the number of CCK-immunopositive cells remained unchanged whereas the number of Ins-positive cells decreased coupled with an increase in the number of Glu-positive cells. The results indicate that both tyrosine kinase and cellular Ca2+ seem to be the intracellular mediators involved with the enhanced secretory responses obtained with a combination of the islet hormones with CCK-8. Moreover, the presence of viable pancreatic islets of Langerhans seems to be associated with the potentiation of the islet hormones with CCK-8.