Ultrastructure of pancreatic acinar and islet parenchyma in rats at various intervals after duct ligation

Systemic inflammation with multiorgan dysfunction is the cause of death in murine ligation-induced acute pancreatitis

BACKGROUND

We have previously shown that distal pancreatic duct ligation-induced acute pancreatitis in mice is associated with substantial mortality.

METHODS

We examined the cause of death in duct ligation-induced acute pancreatitis in mice by serial examination of multiple parameters in three experimental groups: distal pancreatic duct ligation (PD), bile duct ligation alone (BD), and sham operation (S).

RESULTS

BD and S had no mortality, while PD had 94% mortality with most deaths between days 2 and 4. Characteristics of mice with acute pancreatitis included (ANOVA; p < 0.05): extracellular regulated kinase activation in the pancreas and lung; pancreatic neutrophil infiltration and acinar cell necrosis maximal on day 2; increased plasma cytokine and aspartate aminotransferase levels and bronchoalveolar lavage fluid neutrophil count and cytokine levels, peaked on day 3; hypotension and bradycardia were worst on day 4; pulmonary neutrophil infiltration and plasma creatinine level peaked on day 4. Liver injury evidenced by raised aspartate serum transaminase after hepatic obstruction was exacerbated by PD.

CONCLUSIONS

Systemic inflammation with multiorgan dysfunction causes death in pancreatic duct ligation-induced acute pancreatitis in mice. This experimental model is a suitable experimental analogy of "early severe gallstone pancreatitis" to investigate disease pathogenesis and to evaluate novel therapeutic strategies.

A novel model of severe gallstone pancreatitis: murine pancreatic duct ligation results in systemic inflammation and substantial mortality

BACKGROUND

Suitable experimental models of gallstone pancreatitis with systemic inflammation and mortality are limited. We developed a novel murine model of duct-ligation-induced acute pancreatitis associated with multiorgan dysfunction and severe mortality.

METHODS

Laparotomy was done on C57/BL6 mice followed by pancreatic duct (PD) ligation, bile duct (BD) ligation without PD ligation, or sham operation.

RESULTS

Only mice with PD ligation developed acute pancreatitis and had 100% mortality. Pulmonary compliance was significantly reduced after PD ligation but not BD ligation. Bronchoalveolar lavage fluid neutrophil count and interleukin-1β concentration, and the plasma creatinine level, were significantly elevated with PD ligation but not BD ligation. Pancreatic nuclear factor κB (p65) and activator protein 1 (c-Jun) were activated within 1 h of PD ligation.

CONCLUSION

PD-ligation-induced acute pancreatitis in mice is associated with systemic inflammation, acute lung injury, multiorgan dysfunction and death. The development of this novel model is an exciting and notable advance in the field.

Developmental pathways during in vitro progression of human islet neogenesis

Islet neogenesis, or the differentiation of islet cells from precursor cells, is seen in vitro and in vivo both embryonically and after birth. However, little is known about the differentiation pathways during embryonic development for human pancreas. Our previously reported in vitro generation of islets from human pancreatic tissue provides a unique system to identify potential markers of neogenesis and to determine the molecular mechanisms underlying this process. To this end, we analyzed the gene expression profiles of three different stages during in vitro islet generation: the Initially Adherent, Expanded, and Differentiated stages. Samples from four human pancreases were hybridized to Affymetrix U95A GeneChips, and data analyzed using GeneSpring 7.0/9.0 software. Using scatter plots we selected genes with a 2-fold or greater differential expression. Of the 12,000 genes/ESTs present on these arrays, 295 genes including 38 acinar-enriched genes were selectively lost during the progression from the Initially Adherent stage to the Expanded stage; 468 genes were increased in this progression to Expanded tissue; and 529 genes had a two-fold greater expression in the Differentiated stage than in the Expanded tissue. Besides the expected increases in insulin, glucagon, and duct markers (mucin 6, aquaporin 1 and 5), the beta cell auto-antigen IA-2/phogrin was increased 5-fold in Differentiated. In addition, developmentally important pathways, including notch/jagged, Wnt/frizzled, TGFbeta superfamily (follistatin, BMPs, and SMADs), and retinoic acid (COUP-TFI, CRABP1, 2, and RAIG1) were differentially regulated during the expansion/differentiation. Two putative markers for islet precursor cells, UCHL1/PGP9.5 and DMBT1, were enhanced during the progression to differentiated cells, but only the latter could be a marker of islet precursor cells. We suggest that appropriate manipulation of these differentiation-associated pathways will enhance the efficiency of differentiation of insulin-producing beta-cells in this in vitro model.

Pancreatic regenerating protein I in chronic pancreatitis and aging: implications for new therapeutic approaches to diabetes

OBJECTIVES

We investigated the relationship of pancreatic regenerating protein (reg) in models of acinar cell atrophy and aging, and the effect of reg I protein replacement on glucose tolerance.

METHODS

Rats underwent pancreatic duct ligation (PDL) and were followed through 12 months. Aging rats were studied at 12 and 20 months. Intraperitoneal glucose tolerance tests (IPGTTs) were performed, pancreatic reg I, reg I receptor, insulin gene expression, and reg I protein levels were measured. Pancreatic duct ligation and aged animals were treated with exogenous reg I protein and assessed for glucose metabolism.

RESULTS

After PDL, chronic atrophic pancreatitis developed, with a progressive loss of acinar cells and pancreatic reg I. During aging, a similar depression of reg I gene expression was also noted. The reg I levels correlated with pancreatic insulin levels. Twelve months after PDL, IPGTT results were abnormal, which were significantly improved by administration of reg I protein. Aged animals demonstrated depressed IPGTT, which marginally improved after reg I administration. Anti-reg antibody administration to young rats depressed IPGTT to elderly levels.

CONCLUSIONS

Depletion of the acinar product reg I is associated with the pathogenesis of impaired glucose tolerance of pancreatitis-associated diabetes and aging, and replacement therapy could be useful in these patients. Reg I is an acinar cell product, which affects islet function.

Weighing up beta-cell mass in mice and humans: self-renewal, progenitors or stem cells?

Understanding how beta-cells maintain themselves in the adult pancreas is important for prioritizing strategies aimed at ameliorating or ideally curing different forms of diabetes. There has been much debate over whether beta-cell proliferation, as a means of self-renewal, predominates over the existence and differentiation of a pancreatic stem cell or progenitor cell population. This article describes the two opposing positions based largely on research in laboratory rodents and its extrapolation to humans.

Regional differences in the cellular proliferation activity of the regenerating rat pancreas after partial pancreatectomy

The proliferation activity of component cells and its regional differences in the regenerating rat pancreas after 90% pancreatectomy were examined by bromodeoxyuridine (BrdU) immunohistochemistry. Cells of the ductal system and the centroacinar cells showed a rapid increase in labeling indices at day 2 after pancreatectomy, followed by a second peak of a mild increase at days 5 to 7. No regional difference in the labeling index was recognized in the ductal elements. In contrast, the labeling index of acinar cells started to increase at day 3, reaching a definite peak at day 5. Furthermore, acinar cells in the region close to the duodenum had labeling indices more than 2 times higher than those in the portions further away from the duodenum. Acinar cells increased in number as early as from day 3 after surgery. These result suggested that the parental cells of regeneration were located in the ductal epithelium. It is highly probable that the proliferation of acinar cells is controlled by some unknown trophic factor(s) which is released locally from the duodenum, but does not involve a neural or a circulatory route. The phenomenon may be closely linked to the known fact that the incidence of pancreatic cancer is highest in the head region.

Induction of islet cell neogenesis in the adult pancreas: the partial duct obstruction model

The proliferative capacity of adult pancreatic islet cells is limited, although the formation of new islets from cells associated with the ductal epithelium is achievable even in the adult gland. Understanding the mechanism whereby proliferation and subsequent differentiation of putative precursor cells leads the appearance of new islets, i.e., islet neogenesis, may be important as a modality for treatment of both Type I and type II diabetes, in which there is an absolute or relative deficiency of insulin. It appears that certain genes and their protein products are essential to the initiation of the initial step in the pathway. We have shown that partial obstruction of the hamster pancreas is able to reverse streptozotocin-induced diabetes more than 50% of the time. An extract, termed ilotropin, prepared from obstructed pancreata, also reverses the diabetes, whereas extracts of control non-obstructed pancreata do not. Ilotropin contains a protein that is heat and acid stable with MW around 20-45 kDa that is capable of stimulating the proliferation of isolated duct cells in culture. Using mRNA and a differential display technique, 20 genes were found to be expressed in the partially obstructed (regenerating), but not the non-obstructed (non-regenerating) pancreas. One of these islet neogenesis-associated proteins (INGAP) proved to be unique to the obstructed pancreas, and a peptide contained within the sequence was capable of stimulating the proliferation of ductal cells in culture. INGAP was found to be expressed early in the neogenic process before the onset of ductal cell proliferation, and was capable of stimulating tritiated thymidine uptake into protodifferentiated epithelial cells, compatible with the notion that it might be involved in initiating the process of islet neogenesis.

T cell-mediated exocrine pancreatic damage in major histocompatibility complex class II-deficient mice

BACKGROUND & AIMS

Recent observations suggest a role for lymphocytes in human pancreatitis. However, existing animal models of pancreatitis are not immunologically based. In studies on major histocompatibility complex (MHC) II-deficient mice backcrossed five generations onto a C57BL/6 background, we discovered a progressive wasting disease due to pancreatic damage. The purpose of this study was to characterize this model of immune-based pancreatic injury.

METHODS

The pathology was characterized histologically and functionally by assaying for pancreatic enzymes and glucose.

RESULTS

By 6 months, a periductal lymphocytic infiltrate was observed that later developed into pancreatic lesions with extensive, but selective, destruction of acinar cells. Mice eventually lost weight, developed a hunched appearance, and began to pass large, pale pellets. Histology of affected mice revealed pancreatic atrophy with almost complete loss of acinar cells, although islets remained intact. Serum levels of amylase, lipase, and glucose confirmed the selective loss of the exocrine pancreas, with both amylase and lipase levels being significantly decreased in affected mice. However, glucose levels remained unaffected. Adoptive transfer of splenic mononuclear cells to athymic mice was found to transfer the disease.

CONCLUSIONS

Aged MHC II-deficient mice develop an immune-based pancreatitis with selective loss of exocrine cells and function.

The somatostatin receptor-adenylate cyclase system in rat pancreatic acinar membranes after temporary pancreaticobiliary duct ligation

The mechanism whereby somatostatin (SS) produces beneficial effects in established pancreatitis induced by pancreaticobiliary duct ligation (PBDL) is still not clear. The aim of the work was to evaluate the possibility of a direct action of SS on pancreatic acinar cells from rats with acute pancreatitis. For this purpose, we studied the SS-receptor-adenylate cyclase system in pancreatic acinar membranes from both, control rats and rats with experimentally induced acute pancreatitis. On the other hand, it has been reported that cholecystokinin (CCK) diminishes the number of SS receptors in pancreatic acinar cells. Proglumide, a CCK receptor antagonist reduces the severity of acute pancreatitis in the rat. Therefore, we have also examined the effect of proglumide on the somatostatinergic system in controls and rats with acute pancreatitis. Fourteen hours after PBDL, the SS receptors, the capacity of the SS analogue SMS 201-995 to inhibit forskolin-stimulated adenylate cyclase activity and PTX-catalyzed [32P] ADP-ribosylation of the alpha1 subunits of Gi proteins could not be detected in pancreatic acinar membranes. One month after reopening the closed pancreaticobiliary duct (PBD), the pancreas showed regeneration of acinar cells, and the above-mentioned parameters were significantly lower than in the control group. Two months after reopening the closed PBD, all these parameters had returned to control values. The administration of proglumide (20 mg/kg i.p.), a cholecystokinin receptor antagonist, accelerated pancreatic regeneration and approached all these parameters to control values one month after reopening the closed PBD. The present study suggests that the beneficial effects of SS on established pancreatitis induced by PBDL may not be due to a direct action of the peptide on pancreatic acinar cells at least at 14 hours after PBDL. In addition, these findings suggest that in established pancreatitis the effect of proglumide on the SS receptor-adenylate cyclase system could be due to its action on pancreatic regeneration.

Three-dimensional structure of the rat pancreatic duct in normal and inflammated pancreas

We observed the corrosion casts of the Wistar rats' pancreatic ducts with scanning electron microscopy (SEM), and their conventionally fixed pancreatic tissue with SEM and transmission electron microscopy (TEM). These findings revealed the following facts about the three-dimensional structure of pancreatic duct. (1) The interlobular and intralobular ducts branch like a tree, and the intercalated ducts wind and fork into two branches, although parts of the intercalated ducts anastomose with each other. The intercellular secretory canaliculi extend from the central lumina, which run straight through the center of the acini, finally approaching close to the basement membranes of acini. (2) The lumina of pancreatic ducts (i.e., the interlobular up to the intercalated ducts) are cylindric and have smooth surfaces. The luminal surface of each epithelial cell, however, is decorated by numerous microvilli and a single cilium. The length of the latter tends to be short in proportion to the diameter of pancreatic duct. Moreover the epithelial cell surfaces, which border each central lumen, have various densities of microvilli. (3) The intraductal cilium core is provided with nine microtubules, which is different from the number of microtubules encountered within the cilium core of uterine tube or bronchial epithelium. The number of microtubules in the cross-sectioned intraductal cilia decreases toward the distal portion of cilia. SEM and TEM observations on WBN/Kob rats' pancreatic ducts suggest that increased pancreatic ductal pressure causes the helical shape of the pancreatic ductal lumen. Such a helical form might also be caused by the protrusion of epithelial cell boundaries into their lumen and the hypertrophy and hyperplasia of epithelial cells, thus leading to the formation of numerous depressions equipped with elongated cilia.

Effects of cycloheximide on pancreatic endonuclease activity, apoptosis, and severity of acute pancreatitis

The factors that determine the severity of acute pancreatitis are unknown, but a close inverse correlation between that severity and the extent of acinar cell apoptosis that follows the triggering signal has been previously noted [A. M. Kaiser, A. K. Saluja, A. Sengupta, M. Saluja, and M. L. Steer. Am. J. Physiol. 269 (Cell Physiol. 38): C1295-C1304, 1995]. In the present studies, we have evaluated internucleosomal DNA fragmentation and apoptosis within the pancreas and the effects of inhibiting protein synthesis by cycloheximide (CHX) on these phenomena as well as on the severity of pancreatitis. We report the constitutive presence of a Ca(2+)- and Mg(2+)-dependent endonuclease activity within pancreatic nuclei that is dependent on continued protein synthesis. Furthermore, we have found that CHX administration reduces the extent of apoptosis but significantly worsens the severity of pancreatitis that follows ligation of the rat common bile-pancreatic duct. These observations are consistent with the hypothesis that apoptosis is a teleologically beneficial response to acinar cell injury during acute pancreatitis.

Pancreatic regeneration (reg) gene expression in a rat model of islet hyperplasia

BACKGROUND

After pancreatectomy, regeneration of acinar and islet elements occurs. Recent data from a model of islet hyperplasia in the hamster suggested that induction of a local pancreatic factor stimulates islet formation. We postulate that the reg gene may be this factor.

METHODS

We studied reg expression during induction of islet growth by using a similar model in the rat. Rats underwent surgical wrapping of the splenic lobe of the pancreas or sham operation.

RESULTS

At 2 days ductular proliferation and immunohistochemical evidence of insulin within ductular epithelia were evident in the wrapped lobe. By 14 and 56 days islet number per square millimeter increased 63% and 43%, respectively. Reg mRNA levels, measured by Northern blot analysis with a rat reg cDNA probe (n = 5), increased 300% at 2 days in the wrapped lobe and decreased to that of unwrapped controls by 14 days. In situ hybridization showed localization of reg to the acinar cells. In unwrapped gastric lobes of animals who underwent surgical wrapping of the splenic lobe, no change in islet number per square millimeter or reg gene expression was noted.

CONCLUSIONS

Surgical wrapping of the pancreatic splenic lobe induces local reg gene expression that is temporally associated with duct cell hyperplasia. This is followed by islet formation within the wrapped lobe. Reg may play a role in the induction of new islets from ductular precursors and in maintenance of normal islet function.

Islet-cell regeneration in the diabetic hamster pancreas with restoration of normoglycaemia can be induced by a local growth factor(s)

Partial pancreatic duct obstruction in the hamster leads to the induction of endocrine-cell differentiation and new islet formation. We prepared cytosolic extracts from the partially obstructed pancreas and identified one, which when administered i.p., produced significant increases in the incorporation of tritiated thymidine by ductular and islet cells, as well as a corresponding increase in islet mass. In this study, we evaluate the ability of this extract to reverse streptozotocin diabetes mellitus. Hamsters were treated i.p. twice daily for 7 weeks with either 0.9% NaCl (saline) (n = 10) or a cytosol extract (n = 10) prepared previously from partially obstructed hamster pancreata. All animals in the cytosol group survived vs only 60% of the saline group (p = 0.02). Random blood glucose levels were greater than 22.2 mmol/l in 90% of the saline group vs 40% in the cytosol group (p < 0.05). Pancreatic tissue from the surviving saline animals and from persistently hyperglycaemic cytosol-treated animals, showed intra-cytoplasmic vacuolation of islet cells, a characteristic lesion of sustained hyperglycaemic states. Vacuolation was not observed in normoglycaemic extract treated animals. Islets in hyperglycaemic animals demonstrated a profound decrease or absence of immunoreactive insulin, compared to an abundance of immunoreactive beta cells in cytosol-treated animals that reverted to normoglycaemia. In this group, single cells or nests of cells stained for insulin on glucagon cells were identified in ductal epithelium in association with cells budding from the duct. Morphometric analysis of pancreata in reverted cytosol-treated animals showed a new population of small islets compared with saline controls and an increased islet mass. In summary, streptozotocin diabetes can be reversed by new islet formation induced by local pancreatic growth factors, the exact nature of which remains to be determined.

In Vivo Cell Transformation: Neogenesis of Beta Cells from Pancreatic Ductal Cells

During embryogenesis, islet cells differentiate from primitive duct-like cells. This process leads to the formation of islets in the mesenchyme adjacent to the ducts. In the postnatal period, any further expansion of the pancreatic endocrine cell mass will manifest itself either by a limited proliferation of the existing islet cells, or by a reiteration of ontogenetic development. It is the latter, cell transformation by a process of differentiation from a multipotential cell, that will be referred to in this review as islet neogenesis. To better appreciate the mechanisms underlying islet cell neogenesis, some of the basic concepts of developmental biology will be reviewed. Considerable discussion is devoted to the subject of transdifferentiation, a change in a cell or in its progeny from one differentiated phenotype to another, where the change includes both morphological and functional phenotypic markers. While in vitro studies with fetal and neonatal pancreata strongly suggest that new islet tissue is derived from ductal epithelium, what is not established is whether the primary cell is a committed endocrine cell or duct-like cell capable of transdifferentiation. Next, research in the field of β-cell neogenesis is surveyed, in preparation for the examination of whether there is a physiological means of inducing islet cell regeneration, and whether the new islet mass will function in a regulated manner to reverse or stabilize a diabetic state? Our belief is that the pancreas retains the ability to regenerate a functioning islet cell mass in the postnatal period, and that the process of cell transformation leading to islet neogenesis is mediated by growth factors that are intrinsic to the gland. Furthermore, it is our contention that these factors act directly or indirectly on a multipotential cell, probably associated with the ductular epithelium, to induce endocrine cell differentiation. In other words, new islet formation in the postnatal period reiterates the normal ontogeny of islet cell development. These ideas will be fully developed in a discussion of the Partial Duct Obstruction (PDO) Model.

Endocrine tissue associated with the pancreatic ductal system: a light and electron microscopic study of the adult rat pancreas with special reference to a new endocrine arrangement

BACKGROUND

A substantial part of the endocrine pancreas has been previously described as being located either close to the excretory ducts as small clusters of endocrine cells and as Islets of Langerhans, or associated with the ducts as single endocrine cells scattered through the ductal epithelium.

METHODS

Four Wistar white adult rats were sacrificed and perfused via the thoracic aorta with 2.5% glutaraldehyde. After the usual treatment for the transmission electron microscopy, pieces of pancreas were sectioned consecutively for light microscopy. Consecutive ultrathin sections were performed in the most interesting cases.

RESULTS

The observations previously reported were confirmed. In addition, a new endocrine arrangement was detected and described as buds of endocrine cells (mainly B-cells) protruding from the ductal epithelium into the surrounding tissue.

CONCLUSIONS

The authors propose to explain the endocrine buds as components of the gastro-entero-pancreatic system or as a stage of an endocrine pancreatic "neo-histogenesis" occurring in the adult rat pancreas.

Adult pancreatic tissue fate after pancreatic fragment autotransplantation into the spleen of the pancreatectomized dog

As far as we know, after adult enzyme-digested pancreatic fragment autotransplantation, the fate of the inoculated pancreatic tissue has never been reported and the hypothetic engrafted islet mass growth by mitotic division or by a true islet neogenesis from ductular precursor cells has never been demonstrated. In dogs with total or near-total (90%) pancreatectomy that preserves the duodenum and the common bile duct, morphologic study of the pancreatic tissue inoculated into the spleen has demonstrated an exuberant ductular-acinar-islet regenerative process, with progressive cystic degeneration of the newly formed ductular-acinar structures occurring simultaneously with the selective survival and growing predominance of extraductal tissue scattered as distinct islets, clusters of islet cells, or single islet cells. In addition to the B, A2, and D cell types of the normal adult dog islet, we have also seen a peculiar ultrastructural pleomorphism of the insular B cells, frequently combined with their ductular or glandular arrangement in maturing islets. Rare or never before reported islet cell types in the adult dog's islets (G cells, mixed endocrine cells of the A2-D, D-B, and A2-B types, and mixed acinar-islet cells of the D-acinar type) were also putatively identified. Using light microscopy we have identified many mitotic figures on ductular and centroacinar cells in ductules and ductular-acinar structures.(ABSTRACT TRUNCATED AT 250 WORDS)

Cell features in pancreas of prediabetic and diabetic rabbits after Wirsung duct ligation. Histochemical and histoenzymatic studies

Kinetic studies of the histochemical and histoenzymatic behavior of rabbit pancreatic parenchymas were performed 5, 30 and 90 days after Wirsung duct ligation. In control pancreas, some enzyme activities (EA) were more prominent in Langerhans islets [glucose-6-phosphatase, glucose-6-phosphate dehydrogenase (DH), isocitrate DH, glycerol-3-phosphate DH, NADPH DH], others were strongly marked in acini and ducts (alkaline phosphatase, beta-glucuronidase, acid esterase aryl-sulfatase). Histochemical and enzyme abnormalities observed in experimental rabbits reflect the post-ligation degenerative and reactive processes in both exocrine and endocrine pancreas: (1) the decrease in Krebs cycle and pentose pathway linked EA and the increased lysosomal and acid phosphatase EA reflect early (day 5) degeneration and necrosis of islets and acini (day 30); (2) proliferative processes in developed ductal epithelia are shown by an increase in both glycolytic and lysosomal EA (days 30 and 90); (3) connective tissue neogenesis and interstitial fibrosis occurred as shown by activated beta-glucuronidase, aryl-sulfatase, alkaline phosphatase and increased ribonucleoproteins and glycoaminoglycans contents (day 30); (4) on day 90, the neoformed cell clusters presenting glucose-6-phosphatase positivity (B-cell marker) are seen in the pancreas remnant. At the same time, blood insulin level increases correlated with a decrease of hyperglycemia.

Pancreatic structure and glucose tolerance in a longitudinal study of experimental pancreatitis-induced diabetes

Chronic pancreatitis is associated with glucose intolerance and resultant pancreatogenic diabetes. Using the canine pancreatic duct-ligated model of pancreatitis, we serially evaluated pancreatic histology and electron microscopy, tolerance to intravenous and oral glucose, and insulin response to glucose loading. Pancreatic duct ligation caused microscopic evidence of acute pancreatitis at 1 week, progressing to acinar loss and fibrosis consistent with chronic pancreatitis at time periods up to 6 months. The islets of Langerhans showed degranulation early and appeared to be structurally preserved late. Calculated K values indicated a progressive significant deterioration in intravenous glucose tolerance, falling significantly from 3.46 +/- 0.23 basally to 1.51 +/- 0.17 at 6 months after duct ligation (p less than 0.0001). Oral glucose tolerance deteriorated significantly, with the integrated glucose response rising from 23.7 +/- 1.2 g/dl.minute basally to 32.3 +/- 2.8 g/dl.minute at 6 months after duct ligation (p less than 0.05). Integrated insulin response to both intravenous and oral glucose deteriorated with pancreatitis. Pancreatitis-induced glucose intolerance is a consistent feature of this duct-ligated model. Glucose intolerance stabilizes between 4 and 6 months after duct ligation and is associated with pancreatic acinar fibrosis and pancreatic endocrine structural preservation. While the mechanism of altered glucose tolerance may involve mechanical, neural, humoral, or vascular events, our data clearly support the conclusion that pancreatic ductal stenosis with resultant pancreatic fibrosis and chronic pancreatitis is associated with abnormal islet responsiveness leading to circulating insulin deficiency and glucose intolerance, despite histologic and ultrastructural evidence of intact islets of Langerhans.

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.

Effect of duct obstruction on histology and on activities of gamma-glutamyl transferase, adenosine triphosphatase, alkaline phosphatase, and amylase in rat pancreas

The effect of pancreatic duct obstruction on the activities of amylase and three nonexocrine pancreatic enzymes was studied in the rat. gamma-Glutamyl transferase (GGTase) activity, which is localized primarily in the plasma membrane of acinar cells, disappeared from the acinar basolateral plasma membrane and declined in specific activity by 80% over a seven-day experimental period. Mg-ATPase, localized primarily in the apical plasma membrane of acinar cells, simultaneously declined in activity in acinar cells but increased in activity in connective tissue. Mg-ATPase specific activity rose 3.5-fold. The histochemical results showed that the ductlike cells resulting from obstruction were derived primarily from acinar cells. Alkaline phosphatase (APase) activity, which is localized in vascular endothelium and the stroma of interlobular ducts, exhibited a dramatic increase in the periacinar, periductal, and interlobular stroma, and specific activity rose 11-fold. Amylase-specific activity declined as did the protein to DNA ratio. Gel electrophoresis showed that the amount of zymogen granule polypeptides declined after duct obstruction, whereas a few other polypeptides increased in amount.

Neoplasia and hyperplasia of pancreatic endocrine tissue in the rat: an immunocytochemical study

Spontaneously occurring neoplasms and non-neoplastic proliferative changes of the pancreatic cells in aging Sprague-Dawley and Long-Evans rats were examined for the presence and distribution of pancreatic hormones using immunocytochemical techniques. Islet cell tumors were indistinguishable in the two rat strains. They were composed principally of insulin-containing beta cells, but had additional and variable small proportions of cells that stained for somatostatin, glucagon, or rarely, pancreatic polypeptide. The heterogeneity in these spontaneous islet cell neoplasms was similar to that reported in humans as well as those induced in rats by streptozotocin. Hyperplasia of the islet cells also mainly affected the beta cells, but the overall pattern of immunocytochemical staining usually remained similar to that of normal islets, a point of distinction from islet cell neoplasms. In addition, rats with exocrine atrophy and fibrosis were found to have considerable disruption and focal proliferation of the islets.

Development of experimental cancer in the head of the pancreas by surgical induction of tissue injury

The majority of carcinomas of the pancreas in humans are of ductal origin and are located in the head of the gland. These clinical characteristics however, are not affected in traditional animal models of the disease. Partial pancreatic duct obstruction with ductal epithelial hyperplasia was produced in the Syrian golden hamster by wrapping the head of the pancreas with cellophane tape. Wrapped and unwrapped animals were then exposed to an exogenous carcinogen (N-nitrosobis[2-oxopropyl]amine). Assay of serum ribonuclease activity was used as a marker of disease. Invasive lesions developed in both groups of animals. Fifty percent of the tumors in the Group II (cellophane wrap and N-nitrosobis [2-oxopropyl] amine) hamsters were located in the head of the gland and were of ductal origin. All tumors in animals receiving N-nitrosobis [2-oxopropyl]amine alone (Group I) occurred peripherally and were derived from ductular or acinar tissue. Elevation of serum ribonuclease activity was noted early in the course of carcinogenesis, thereafter returning to normal, which may explain the clinical controversy regarding this marker. This new model should enhance our knowledge of the interrelationships between etiologic factors, precursor lesions, and pancreatic cancer.

A new approach to the induction of duct epithelial hyperplasia and nesidioblastosis by cellophane wrapping of the hamster pancreas

There is ample evidence that a relationship exists between duct epithelial hyperplasia and carcinoma of the pancreas. However, no experimental system exists to investigate the mechanisms involved. A new model is described in the Syrian golden hamster for inducing duct epithelial hyperplasia and nesidioblastosis. The head of the pancreas is wrapped with cellophane tape; ligation of the duct is not involved and there is no evidence of diffuse pancreatitis. Preliminary studies have revealed that this model results in periductal fibrosis in relation to the cellophane thus producing partial duct obstruction. Concomitant with the fibrosis there is duct epithelial hyperplasia in the head of the gland, while peripherally there is ductular proliferation and the initiation of nesidioblastosis. It is believed that this model will be of use in studies of pancreatic carcinogenesis and will thus enhance our knowledge of the interrelationships between etiologic factors, precursor lesions, and pancreatic cancer. This is of particular importance in the early recognition of this neoplasm in man.

An autoradiographic study of the cell proliferation during involution of the rat pancreas

After ligation of the rat pancreas, DNA synthesis in centoacinar cells and cells of the intercalary ducts, proximal and distal to the ligature, was suppressed for about 18 hr. This preceded a large increase in thymidine labelling of the nuclei of these cells. The increase in the thymidine indices was much greater and more prolonged in the distal pancreas where duct-like structures were formed that replaced the acini. DNA synthesis in acinar cells proximal to the ligature was suppressed for 36 hr preceding an increase in the thymidine indices much smaller than that in the duct cells. DNA synthesis in acinar cells distal to the ligature ceased and the acinar cells progressively died. We propose that the pancreas is composed of proliferative units, each comprising acinar cells, centroacinar cells and intercalary ducts, which react as a whole when acinar cell loss occurs in pathological processes.

Cells of origin of pancreatic cancer: experimental animal tumors related to human pancreas

Human pancreatic adenocarcinoma is traditionally believed to be ductal in origin, primarily due to the presence of complexes of tubules interpreted as being derived from ductular proliferation. Although observations in various animal models of pancreatic tumors suggested that acinar cells wee undergoing dedifferentiation to form tubular complexes, this process was difficult to reconcile with an acinar arrangement of the pancreas. Using three-dimensional reconstructions and retrograde injections, it was concluded that the normal pancreas actually has a tubular arrangement. The tubules branch, curve, and anastomose. By losing zymogen granules and decreasing in height, acinar units become recognized as ductule-like structures. Therefore, the presence of tubular complexes should not be taken to indicate that carcinogenesis has taken place or to eliminate acinar cells as possible cells of origin of adenocarcinoma, which by present criteria would be classified as ductal.

Architecture of normal pancreas as revealed by retrograde injection

The architecture of the pancreas was revealed by retrograde injection of the pancreatic ductal system of normal rats with a silicone rubber compound, and subsequent study of the preparation by light microscopy and scanning electron microscopy. The injected material became associated with both ducts and "acinar" areas. Examination of these specimens suggests that the arrangement of the exocrine pancreas is that of a complexly curving and branching system of tubules which anastomose and end blindly. This architecture, which is not that of a true acinar gland, provides a rational basis for the understanding of the simple dedifferentiative changes that accompany pancreatic carcinogenesis, and which have been generally interpreted as representing ductular proliferation.

Release of insulin in vitro from normal and duct-ligated rat pancreas

Ligation of the pancreatic duct causes atrophy of the acinar cells but leaves the endocrine tissue intact. In the present study, a partial ligation of the pancreatic duct was performed in the rat, and the in vitro insulin response to glucose was compared from both the atrophic and non-atrophic portions of the pancreas. Subsequent morphological studies of the duct-tied portion of the pancreas indicated a complete lack of acinar cells and a possible neoformation of ducts, fat cells and connective tissue. However, islets were present in normal amounts and appeared well perserved. Measurements of the insulin release in vitro from this ligated pancreatic tissue showed that an increase of the glucose concentrations from 3.3 to 16.7 mmol/1 resulted in a six-fold stimulation. A further two-fold stimulation was seen after addition of theophylline to the high-glucose incubation medium. In addition, only under the latter conditions was there a significantly increased insulin release from both non-atrophic portion of the pancreas and from the pancreas of sham-operated animals. It is concluded that duct ligation does not diminish the glucose sensitivty of rat islet B-cells. Thus, the present study does not support the view proposed previously that islet tissue is functionally of a foetal nature following duct ligation.

Long-term hormonal secretion from the autotransplanted sheep pancreas

Seventy-five duct-ligated pancreatic segmental autotransplants were made into bipedicled skin loops on the necks of merino ewes by vascular suture to the carotid artery and jugular vein; the in situ pancreatic remnants apparently continued to function normally. Thirty-seven were found to be active hormone secretors (secretion-rate responses to Na butyrate greater than 1 mU/min for insulin or 5 ng/min for glucagon) when first tested approximately 1 month after transplantation; 12 remained active at 1 year, 5 at 2 years, and 4 at 3 years. At first testing, the responses were (mean +/- standard errors): insulin, 12.3 +/- 2.52 mU/min; glucagon, 52.6 +/- 13.5 ng/min. It is concluded that this autotransplant can, on occasion, be relatively long-lived and that it is a useful model with which to study not only pancreatic physiology but also non-immunological factors involved in survival of endocrine function in pancreatic transplants.

Anastomosing tubular arrangement of the exocrine pancreas

Wax reconstructions of zymogen-containing cells in rat show the arrangement of the exocrine pancreas to be a branching, anastomosing system of tubules which vary in diameter and end blindly. This arrangement is not that of a true acinar gland.

Subcutaneous, isogeneic transplantation of duct-ligated pancreas in streptozotocin diabetic mice: relationships between recovery and hormone contents in transplants or host pancreas

Recovery from diabetes was observed in streptozotocin-treated mice that received subcutaneous, isogeneic transplants of duct-ligated pancreas. Transplants excised from recovered hosts contained both immunoreactive insulin (IRI) and glucagon (IRG), indicating that both A and B cells capable of hormone storage were present. The IRI content in transplants, although only one sixth of that transplanted 6 wk earlier, was still 21/2 times greater than that in the host pancreas and was inversely related to the plasma glucose of the recipient during and after recovery. The IRI content in the transplant added to that in the host pancreas totaled 13% of the IRI found in the normal mouse pancreas, which sufficed for over-all recovery from diabetes but was insufficient to provide normal glucose tolerance and insulin response to a major glucose challenge. The abnormally high content of glucagon noted in the pancreas of hyperglycemic, sham transplanted mice was reduced by one-half in the pancreas of those transplanted mice returning to normal plasma glucose and insulin. Thus, the insulin content of the transplant was important to the recovery of isografted mice, but in addition, and perhaps as a consequence of recovery, there was a slight increase in the insulin storage capacity of the host pancreas and a marked reduction of glucagon compared to the content of these hormones in the pancreas of hyperglycemic, sham transplanted mice.