Nestin is expressed in vascular endothelial cells in the adult human pancreas.

In this study we examined the expression of nestin in islets, the exocrine part, and the big ducts of the adult human pancreas by immunofluorescent double staining. Two different anti-nestin antisera in combination with various pancreatic and endothelial markers were employed. Nestin-immunoreactive cells were found in islets and in the exocrine portion. All nestin-positive cells co-expressed the vascular endothelial markers PECAM-1 (CD31), endoglin (CD105), and CD34 as well as vimentin. Endocrine, acinar, and duct cells did not stain for nestin. We also demonstrated that in the area of big pancreatic ducts, nestin-positive cells represent small capillaries scattered in the connective tissue surrounding the duct epithelium and do not reside between the duct cells. We detected nestin-expressing endothelial cells located adjacent to the duct epithelium where endocrine differentiation occurs. We have shown that nestin is expressed by vascular endothelial cells in human pancreas, and therefore it is unlikely that nestin specifically marks a subpopulation of cells representing endocrine progenitors in the adult pancreas.     

Development of the endocrine pancreas during larval phases of Rana temporaria

Summary The pancreatic endocrine component was studied at different stages of development in the tadpoles of Rana temporaria. The material was embedded in Epon, and serial semithin and thin sections were made in order to correlate ultrastructural features and tinctorial traits of the endocrine cells. Serial semithin sections were also stained with the peroxidase-antiperoxidase immunocytochemical method and with silver impregnations for argyrophilia and argentaffinity. In early larvae (legless tadpoles), A and B cells are present. Both can be found within ducts and exocrine tissue or, more frequently, in cellular clusters among the ducts and acini. These primitive islets are solid structures, surrounded but not penetrated by capillaries. Mitoses were observed in A and B cells. In the following phase (tadpoles with hindlegs), D and pancreatic polypeptide-immunoreactive cells are also present, as well as numerous endocrine cells scattered among exocrine tissue. There is also a change in the vascular-insular pattern: capillaries not only surround but also penetrate the endocrine group. The structure of the endocrine pancreas in older tadpoles is similar. Tinctorial traits and ultrastructural features of endocrine cells are described, and the origin of primitive islets is discussed.     

Formation of human islands of Langerhans cells from the epithelium of the acini and ducts]

The contents of endocrine cells in the epithelium of ducts and the number of acino-insular elements in exocrine parenchyma and in pancreatic islets were estimated by means of the dotted method in semithin sections prepared from the pancreas of the human embryos (4--7 months of embryogenesis) and of adult persons (40--50 years of age). Endocrine cell formation was noted in all stages studied in ontogenesis. Quantitative data demonstrated that the epithelium of the ducts is the main source for insulocyte formation. In the pancreas of both human embryos and adult persons, acino-insular transformation participated in the formation of endocrine elements. The data obtained gave a certain evidence on entodermal origin of the pancreatic islets in the human pancreas.     

Immunohistochemical study of the developing endocrine pancreas of the opossum (Didelphis virginiana)

Cells immunoreactive for insulin, glucagon, somatostatin, bovine pancreatic polypeptide and 5-hydroxytryptamine are found in the pancreas of the newborn opossum and of all later stages examined. All immunoreactive cell types are present in primary and secondary islets and within elements of the exocrine pancreas. Cells immunoreactive for glucagon, bovine pancreatic polypeptide, somatostatin and 5-hydroxytryptamine generally are confined to the periphery of secondary (intralobular) islets, whereas insulin-immunoreactive cells occupy the central region. Endocrine cells within primary (interlobular) islets are randomly scattered. A small number of pancreatic-polypeptide-immunoreactive cells are reactive for the amine 5-hydroxytryptamine also, but the reverse is not observed. The endocrine pancreas continues to differentiate and develop throughout postnatal life and into adulthood. Little difference was observed between the head and tail regions of the opossum pancreas for the measurements made.     

Development of endocrine pancreatic islets in embryos of the grass snake Natrix natrix (Lepidosauria,Serpentes)

Differentiation of the pancreatic islets in grass snake Natrix natrix embryos, was analyzed using light, transmission electron microscopy, and immuno-gold labeling. The study focuses on the origin of islets, mode of islet formation, and cell arrangement within islets. Two waves of pancreatic islet formation in grass snake embryos were described. The first wave begins just after egg laying when precursors of endocrine cells located within large cell agglomerates in the dorsal pancreatic bud differentiate. The large cell agglomerates were divided by mesenchymal cells thus forming the first islets. This mode of islet formation is described as fission. During the second wave of pancreatic islet formation which is related to the formation of the duct mantle, we observed four phases of islet formation: (a) differentiation of individual endocrine cells from the progenitor layer of duct walls (budding) and their incomplete delamination; (b) formation of two types of small groups of endocrine cells (A/D and B) in the wall of pancreatic ducts; (c) joining groups of cells emerging from neighboring ducts (fusion) and rearrangement of cells within islets; (d) differentiated pancreatic islets with characteristic arrangement of endocrine cells. Mature pancreatic islets of the grass snake contained mainly A endocrine cells. Single B and D or PP–cells were present at the periphery of the islets. This arrangement of endocrine cells within pancreatic islets of the grass snake differs from that reported from most others vertebrate species. Endocrine cells in the pancreas of grass snake embryos were also present in the walls of intralobular and intercalated ducts. At hatching, some endocrine cells were in contact with the lumen of the pancreatic ducts.     

Role of VEGF-A in vascularization of pancreatic islets

Blood vessel endothelium has been recently shown to induce endocrine pancreatic development. Because pancreatic endocrine cells or islets express high levels of vascular endothelial growth factors, VEGFs, we investigated the role of a particular VEGF, VEGF-A, on islet vascularization and islet function. By deleting VEGF-A in the mouse pancreas, we show that endocrine cells signal back to the adjacent endothelial cells to induce the formation of a dense network of fenestrated capillaries in islets. Interestingly, VEGF-A is not required for the development of all islet capillaries. However, the few remaining capillaries found in the VEGF-A-deficient islets are not fenestrated and contain an unusual number of caveolae. In addition, glucose tolerance tests reveal that the VEGF-A-induced capillary network is not strictly required for blood glucose control but is essential for fine-tuning blood glucose regulation. In conclusion, we speculate that islet formation takes place in two sequential steps: in the first step, signals from blood vessel endothelium induce islet formation next to the vessels, and in the second step, the islets signal to the endothelium. The second step involves paracrine VEGF-A signaling to elaborate the interaction of islets with the circulatory system.     

Islet Formation during the Neonatal Development in Mice

The islet of Langerhans is a unique micro-organ within the exocrine pancreas, which is composed of insulin-secreting beta-cells, glucagon-secreting alpha-cells, somatostatin-secreting delta-cells, pancreatic polypeptide-secreting PP cells and ghrelin-secreting epsilon-cells. Islets also contain non-endocrine cell types such as endothelial cells. However, the mechanism(s) of islet formation is poorly understood due to technical difficulties in capturing this dynamic event in situ. We have developed a method to monitor beta-cell proliferation and islet formation in the intact pancreas using transgenic mice in which the beta-cells are specifically tagged with a fluorescent protein. Endocrine cells proliferate contiguously, forming branched cord-like structures in both embryos and neonates. Our study has revealed long stretches of interconnected islets located along large blood vessels in the neonatal pancreas. Alpha-cells span the elongated islet-like structures, which we hypothesize represent sites of fission and facilitate the eventual formation of discrete islets. We propose that islet formation occurs by a process of fission following contiguous endocrine cell proliferation, rather than by local aggregation or fusion of isolated beta-cells and islets. Mathematical modeling of the fission process in the neonatal islet formation is also presented.     

Histogenesis of the endocrine pancreas in newborn rats after destruction by streptozotocin. An immunocytochemical study

Endocrine pancreatic tissue in newborn rats was studied 1 to 17 days after the destruction of B cells by an injection of streptozotocin. Regeneration of insulin cells was observed four days after streptozotocin injection, which was followed by recovery from the diabetic state and an increased pancreatic insulin content. Regeneration was characterised by new islets budding from small ducts. The pancreas of newborn rats, like the embryonic pancreas, thus retains a capacity to form endocrine tissue, although some degree of reduplication of preexisting B cells may also be involved in the process. Newborn rats injected with streptozotocin constitute an interesting model for the study of factors which may act on the regenerative potential of pancreatic endocrine tissue in the diabetic state.     

The volume and area of the capillaries in the endocrine and exocrine pancreas of the rat

The capillary volumes in the endocrine and exocrine parenchyma of the pancreas were compared with a point-sampling technique. The islets were found to have a capillary volume of approximately 3.5%, while the value for the exocrine pancreas was significantly (P less than 0.001) lower at 2%. When the capillary wall area was measured, however, both types of parenchyma had a similar value of approximately 20 mm2/mm3 tissue. The reason for the discrepancy between these parameters is probably the lack of lymphatic capillaries, with their relatively small lumen in the islets.     

Microangioarchitecture of the islets of Langerhans in the snakes,Naja naja,Vipera russelli,andEchis carinatus

Summary Due to a decided lack in the literature of reports on the microangioarchitecture of the pancreas of snakes, an analysis was performed in three different species of two different ophidian families with the use of cast preparations and complementary scanning electron microscopy. The vascular architecture reflects the lobular substructure of the pancreas; the organ is supplied by branches of the superior mesentric artery. Coiled lobular arteries and arterioles continue into a meshwork of capillaries. Dilated capillaries of the endocrine portion of the pancreas are an integral component of this fine capillary network. A few very small capillaries establish a connection between the endocrine and the exocrine pancreas. The other capillaries drain into venules, which ultimately join their respective veins. No interspecific differences were noted in the vascularization of the pancreas of the three ophidian species examined. The present results suggest the existence of arterio-venous anastomoses and speak against the presence of a portal system, but establish a feed-forward capillary connection from the endocrine to the exocrine component of the ophidian pancreas.     

Postnatal development of the pancreas in the opossum. Light microscopy.

The pancreas of the newborn opossum consists of a central region of forming islets surrounded by primitive tubules that end in proacinar cells. Paratubular buds, which are outgrowths from the tubular epithelium, characterize the newborn pancreas and eventually give rise to both exocrine and endocrine units. 4 days after birth, definite intralobular ducts, acini and centroacinar cells are observed. In addition to the central expanding islets (primary islets), endocrine cells are observed singly or in small groups in the ductal epithelium. The endocrine cells are believed to originate from the terminal cells of the ductal epithelium and, throughout the entire postnatal period, retain a close association with the exocrine epithelium. With the simultaneous proliferation of both endocrine and exocrine components from the ductal system, the majority of the islets observed at 24 days (5.0 cm) appear to be surrounded by a single layer of acinar cells. As acini develop and the ducts expand toward the periphery, this layer of acinar cells separates from the developing islets, the majority of which have become localized within the centers of lobules to form the secondary islets by the 10.0-cm stage (59 days). A marked development of lobules is observed by the 13.0-cm stage and the majority of acinar cells now are filled with zymogen granules. Acinar cells continue to proliferate late into the postnatal period and the majority of acini exhibit a tubular form in the juvenile and adult opossum.     

Intrahepatic pancrease in Sparus datnia (Ham. Buch.), a Sparidae of the Persian Gulf]

A fish, Sparus datnia (Ham. Buch.), Sparidae, protandric, is one of the species, which has a diffusing intrahepatic pancreas. The gland is compound of two parts : the exocrine part (follow the branches of the portal vein), and the endocrine part (langerhans islets, more or less abundent in the external side of the endocrine part). Three kinds of granular cells are recognized in the endocrine islets.     

Immunocytochemical study of the distribuition of endocrine cells in the pancreas of the Brazilian sparrow species Zonotrichia Capensis Subtorquata (Swaison, 1837).

In the present study, we investigated types of pancreatic endocrine cells and its respective peptides in the Brazilian sparrow species using immunocytochemistry. The use of polyclonal specific antisera for somatostatin, glucagon, avian pancreatic polypeptide (APP), YY polypeptide (PYY) and insulin, revealed a diversified distribution in the pancreas. All these types of immunoreactive cells were observed in the pancreas with different amounts. Insulin-Immunoreactive cells to (B cells) were most numerous, preferably occupying the central place in the pancreatic islets. Somatostatin, PPA, PYY and glucagon immunoreactive cells occurred in a lower frequency in the periphery of pancreatic islets.     

Generation of living color transgenic zebrafish to trace somatostatin-expressing cells and endocrine pancreas organization

In the present study, both gfp and rfp transgenic zebrafish lines using a 2.5-kb zebrafish somatostain2 (sst2) promoter were generated. During embryonic development, expression of GFP/RFP in the endocrine pancreas of transgenic embryos was initiated at ∼20 hpf and the number of GFP/RFP positive cells in the pancreas increased in subsequent stages; thus, our newly generated Tg(sst2:gfp) and Tg(sst2:rfp) lines faithfully recapitulated sst2 expression in endocrine pancreatic cells and provided a useful tool in analyzing the development of Sst2-producing δ-cells in the pancreas. By crossing these new transgenic lines with previously available transgenic lines targeted in insulin (Ins)-producing β-cells, Tg(ins:gfp) and Tg(ins:rfp), in combination with immunodetection of glucagon (Gcg)-producing α-cells and pancreatic polypeptide (PP)-producing PP-cells, the organization and composition of endocrine islets were investigated in both embryonic and adult pancreas. We found that there was always a big cluster of endocrine cells (principal islet) in the anterior-dorsal pancreas, followed by numerous smaller clusters (variable in size) of endocrine cells (secondary islets) along the anterior–posterior axis of the pancreas. All four types of endocrine cells were found in the principal islet, but secondary islets may or may not contain PP-cells. In addition, there were also discrete endocrine cells throughout the pancreas. In all co-localization experiments, we did not find any endocrine cells positive for more than one hormone markers, suggesting that these endocrine cells produce only a single hormone. In both principal and secondary islets, we found that β-cells were generally located in the center and non-β cells in the periphery; reminiscent of the “mantel–core” organization of islets of Langerhans in mammals where β-cells form the core and non-β-cells the mantel. In zebrafish primary islet, β-cells constitute most of the mass (∼50%), followed by δ-cells and α-cells (20–25% each), and PP-cells (1–2%); this is also similar to the composition of mammalian islets.     

Variation in plasma glucose and pancreatic β cells in the turtle, Lissemys punctata (order: Chelonia; family: Trionychidae)

The present study relates to the determination of the plasma glucose level and volumetric analysis of β cells in pancreatic islets of the soft‐shelled turtle Lissemys punctata during different phases of its reproductive cycle. Reproductive events play a vital role in influencing the plasma glucose level and β‐cell behaviour in the pancreatic islets. The colour of the pancreas is either yellowish or pinkish, depending on endocrine activity. Islets are present throughout the gland and range from individual cells to small or large clumps, depending on the seasonal cycle. Splenic islets are dense with more blood capillaries and nerve innervations irrespective of sex and season. The endocrine cell mass forms irregular patches without connective tissue capsule. β cells occupy the inner region of the islets, being surrounded by other cell types. Lissemys punctata exhibits higher β‐cell activity during hibernation. Most insulin‐secreting cells acquire a larger size during the regressive period. An analysis indicates that β cells outnumber the non‐β endocrine cell mass in both number and per cent volume. There is negative correlation between islet mass and animal weight. Between the periods of reproductive cycles, a difference exists with respect to fasting plasma glucose and β‐cell volume.     

Dissociation of Langerhans islets in the rabbit after pancreatic duct ligation. Immunocytochemical and ultrastructural studies

In the rabbit, pancreatic duct ligation leads to serious disturbances of the pancreatic endocrine parenchyma. Immunocytochemical studies conducted over a short period (between 5 and 30 days post ligation) allow observation of a progressive dissociation of the Langerhans islets which initially affects the splenic part of the pancreas, a region where numerous large islets are found. This dissociation is followed by a dispersion of small heterologous endocrine cell clusters or isolated endocrine cells in a connective tissue which replace the exocrine parenchyma. On the 30th day after ligation ultrastructural studies show marked degranulation of the B cells demonstrating the great fragility of these cells. These observations of insular dissociation, scattering of the different endocrine cells and impairment of B cells are often reported in experimental and pathological studies of the pancreas.     

Ontogeny of the endocrine pancreas

The ontogenesis of the endocrine pancreas has been a subject of controversy. The discussion essentially was about organogenesis and histogenesis of islets of Langerhans. Now, the endodermic origin seems well established by several experimental approaches. The variation of the aspects of the islets and of the number of endocrine cells are re-called as well as the functional activity during fetal life. Numerous neuropeptides have been found in endocrine pancreas, so the content of the different endocrine cell types is reviewed with respect to the classic hormones.