Stimulation of islet cell proliferation enhances pancreatic ductal carcinogenesis in the hamster model.

Previous studies have shown that some N-nitrosobis (2-oxopropyl)amine (BOP)-induced ductal/ductular pancreatic cancers in the hamster model develop within islets and that streptozotocin (SZ) pretreatment that caused islet degeneration and atrophy inhibits pancreatic cancer induction. Hence, it appears that in this model islets play a significant role in exocrine pancreatic carcinogenesis. To examine whether stimulation of islet cell proliferation (nesidioblastosis) enhances pancreatic exocrine cancer development, we tested the effect of the pancreatic carcinogen BOP in hamsters after induction of nesidioblastosis by cellophane wrapping. Before wrapping, hamsters were treated with SZ to inhibit pancreatic tumor induction in the unwrapped pancreatic tissues. Control groups with a wrapped pancreas did not receive SZ. Six weeks after SZ treatment, all hamsters were treated with BOP (10 mg/kg body weight) weekly for 10 weeks and the experiment was terminated 38 weeks after the last BOP treatment. Many animals recovered from their diabetes at the time when BOP was injected and many more after BOP treatment. Only nine hamsters remained diabetic until the end of the experiment. Both SZ-treated and control groups developed proliferative and malignant pancreatic ductal-type lesions primarily in the wrapped area (47%) but less frequently in the larger segments of the pancreas, including the splenic lobe (34%), gastric lobe (13%), and duodenal lobe (6%). Only a few lesions developed in the unwrapped pancreatic region of nine diabetic hamsters with atrophic islets, whereas seven of these hamsters had tumors in the wrapped area. Histologically, most tumors appeared to originate from islets, many invasive carcinomas had foci of islets, and some tumor cells showed reactivity with anti-insulin. The results show that, in the BOP hamster model, islets are the site of formation of the major fraction of exocrine pancreatic cancer and that induction of nesidioblastosis enhances pancreatic carcinogenesis.     

Experimental evidence for the origin of ductal-type adenocarcinoma from the islets of Langerhans.

To investigate the role of the islets of Langerhans in pancreatic carcinogenesis, freshly isolated islets from male Syrian hamsters were transplanted into the right submandibular glands of 50 female hamsters that were or were not pre-treated with streptozotocin. Thyroid gland fragments, cellulose powder, and immortal hamster pancreatic ductal cells were injected into the left submandibular gland of the same hamsters. All recipient hamsters were then treated with the potent pancreatic carcinogen N-nitrosobis(2-oxopropyl)amine weekly at a dose of 40 mg/kg of body weight for 3 weeks. Between 3 and 8 weeks later, 18 of 75 (24%) hamsters developed large ductal-type adenocarcinomas in the submandibular gland region, where islets were transplanted, but none developed tumors in the left submandibular gland. In 9 of 18 hamsters, tumors were multiple so that a total of 31 cancers were found. Eleven of these carcinomas were in the vicinity of transplanted islets, eight of which showed intra-insular ductular or cyst formation as seen in the pancreas of hamsters during pancreatic carcinogenesis. The formation of ductular structures within islets was also demonstrated in vitro. Some tumor cells in the vicinity of these islets were reactive with anti-insulin. Y chromosome message was found by polymerase chain reaction analysis in one of the three tumors examined. Also, like the induced pancreatic tumors, all three submandibular gland tumors that were examined had the mutation of the c-Ki-ras oncogene at codon 12 and all tumors expressed blood group A antigen. These and other findings strongly suggest that some components of islets, most probably stem cells, are the origin of ductal-type adenocarcinomas in this model.     

Modification of pancreatic carcinogenesis in the hamster model. 2. The effect of partial pancreatectomy.

The effect of partial pancreatectomy (PP) on the pancreatic carcinogenicity of N-nitrosobis (2-oxopropyl)amine (BOP) was investigated in Syrian golden hamsters by subcutaneous injection of a single dose of BOP (20 mg/kg, body weight) given 30 minutes after (Group 1), 1 week after (Group 2), or 1 week before 70% PP (Group 3). Additional groups consisted of animals with PP alone (Group 4), sham operation (laparotomy) followed 30 minutes later by BOP treatment (Group 5), and BOP treatment only (Group 6). The experiment was terminated 46 weeks after BOP administration in each group. The pancreas and extrahepatic bile ducts, including the common duct and gallbladder, were examined histologically. Tumor patterns were compared in hamsters with PP and in the corresponding segments of the pancreas in BOP-treated control groups. The pancreatic cancer incidence was highest (31%) in Group 2 and lowest in Group 1 (3%), a difference that was statistically significant (P less than 0.01). Also, a statistically highly significant larger number of tumors occurred in Group 2, compared with group 1, 3, or 5 (P less than 0.0005). In a comparison of the number of carcinomas per tumor-bearing hamster, there were greater numbers of carcinomas in Group 2 (2.6 carcinomas) than in Groups 1, 3, 5, and 6 (1.0, 1.0, 1.3, and 2.6 tumors, respectively). Moreover, pancreatic tumors in Group 2 hamsters were larger (average diameter, 10 mm) than in Group 1 (4 mm), Group 3 (3.5 mm), Group 5 (4 mm), and Group 6 (average, 9mm). The incidence of extrapancreatic tumors did not vary among the PP groups but was equally lower than those in BOP-treated control groups. The data indicated BOP carcinogenesis was inhibited by surgery (regardless of whether PP was per formed) when the carcinogen was given 30 minutes after the surgery but was significantly enhanced when BOP was administered 1 week after PP. The possible reasons for these conflicting results are discussed. Morphologically all tumors were of ductular, ductal, and mixed ductular-insular patterns and most developed at the resected margins, where proliferation of islets, ducts, and ductules, but not of acinar cells, occurred. The results confirm our view that the ductal and ductular cells are the progenitor cells for BOP-induced pancreatic tumors in hamsters.     

Modification of pancreatic carcinogenesis in the hamster model. 7. Inhibitory effect of bethanechol chloride

Experiments were designed to investigate in the hamster model the effect on pancreatic carcinogenesis of bethanechol chloride (BC), which is known to increase pancreatic protein synthesis in rats. Hamsters received a single (15 mg/kg body weight) dose of BC either before, simultaneously with, or after a single dose of N-nitrosobis(2-oxopropyl)amine (BOP; 20 mg/kg body weight). A second group was treated daily with BC (7.5 mg/kg body weight) for 24 weeks, following BOP. The control groups consisted of animals treated with BOP only, with BC only, and with solvent only. The surviving hamsters were killed 46 weeks after BOP treatment. BC, whether given before, simultaneously with, or after BOP, significantly reduced the incidence of pancreatic ductal/ductular carcinomas. The multiplicity, size, and latency of carcinomas were also affected by BC. A more pronounced inhibition of cancer induction occurred in the group treated daily with BC after BOP. The possible mechanisms involved in the inhibitory action of BC on pancreatic carcinogenesis are discussed.     

In vitro induction of giant cell tumors from cultured hamster islets treated with N-Nitrosobis(2-Oxopropyl)amine

Giant cell carcinoma of the pancreas is a rare tumor. Its histogenesis is still controversial. In a Syrian hamster pancreatic cancer model, tumors similar to human giant cell carcinomas have been induced at an extremely low rate of incidence and after the use of high doses of pancreatic carcinogens. Thus far no tumors of giant cell type have been induced by the in vitro treatment of hamster pancreatic ductal cells with the potent pancreatic carcinogen N-nitrosobis(2-oxopropyl)amine (BOP). In the present study we report the induction of giant cell carcinoma from hamster islets treated with BOP in vitro. The results suggest that in hamsters some component of islet cells, probably stem cells, are the origin of giant cell carcinoma.     

Modification of pancreatic carcinogenesis in the hamster model. 6. The effect of ductal ligation and excision

The effect of ligation and excision of the pancreatic duct in pancreatic carcinogenesis was examined in the hamster model. Animals were treated with a single dose (20 mg/kg body weight) of N-nitrosobis(2-oxopropyl)amine (BOP) either immediately (Group 1) or on Days 1 (Group 2), 3 (Group 3) or 7 (Group 4) after ligation and excision of the duct of the splenic lobe. Group 5 received BOP shortly after laparoscopy, and Group 6 consisted of BOP-treated controls. All hamsters were killed 46 weeks after BOP treatment. The results showed that despite advanced atrophy of the splenic lobe distal to the excised duct in Groups 1-4, some hamsters in Groups 2, 3, and 4 showed hyperplasia, dysplasia, and increased mitotic activities of ductal and ductular cells. However, carcinomas in the duct-excised atrophic lobe were found only in Groups 1-3. These data indicate that BOP carcinogenesis is mediated through blood circulation, and that cancer development is not inhibited in the duct-excised lobe for up to 3 days after surgery. However, in the entire pancreas, a significant reduction in tumor incidence was seen when the carcinogen was given immediately, or to a lesser extent, 1 day after surgery, regardless of whether or not excision was made. On the contrary, BOP, when given 3 and 7 days after duct excision, enhanced tumor development in the nonexcised (intact) pancreas, compared with other test groups and with BOP controls. Both inhibition and enhancement seemed due to a proportional decrease and increase, respectively, of BOP-responsive cells throughout the intact pancreas.     

Alterations in pancreatic islet function produced by carcinogenic nitrosamines in the Syrian hamster.

Exposure of hamsters to 5 daily doses of 20 mg/kg N-nitrosobis(2-oxopropyl)amine (BOP) or 76 mg/kg N-nitroso(2-hydroxypropyl)(2-oxopropyl)amine (HPOP), resulted in reduced insulin secretion in freshly isolated pancreatic islets. These treatments also reduced plasma insulin and glucose levels, and were hepatotoxic. The inhibition of insulin secretion, however, was transient. Islets isolated from treated hamsters that were then placed in culture secreted elevated levels of insulin for many months. When cultured islets were directly exposed to the nitrosamines for 3 days, there was also a transient reduction of insulin secretion that was subsequently normalized after removal of the nitrosamine from the medium. These results show that BOP and HPOP modify beta-cell function both directly, and possibly indirectly, via damage to the liver. Furthermore, the lack of immediate inhibition of insulin secretion when islets were incubated in the presence of BOP or HPOP as well as glucose, suggests that the nitrosamines do not bind to the glucose receptor.     

Early changes in islet hormone secretion in the hamster pancreatic cancer model

The diabetic state that is seen at a high frequency in association with pancreatic cancer is characterized by elevated plasma levels of several islet hormones and by marked insulin resistance. Both the diabetic state and insulin sensitivity improve after tumor removal by sub-total pancreatectomy. Impaired glucose tolerance has also been found in the hamster pancreatic cancer model, but conflicting data regarding islet function have been reported. In order to further investigate islet function and secretion during early development of pancreatic cancer, we measured the concentrations of insulin, glucagon, somatostatin, and islet amyloid polypeptide (IAPP) in plasma, pancreatic tissue, and secretin-stimulated pancreatic juice at 12 and 27 weeks after the ductal-cell-specific carcinogen, BOP had been used to induce tumors in Syrian golden hamsters. At 12 weeks after BOP, plasma glucagon levels were significantly increased. An exaggerated plasma-glucose response and concomitant hyperinsulinemia were observed at 27 but not 12 weeks after BOP. Plasma IAPP concentrations, but not glucagon or somatostatin, were elevated at 27 weeks. Tissue concentrations of IAPP were substantially reduced in BOP-treated hamsters at 27 weeks. No differences in hormone concentrations were seen in pancreatic juice from the two groups at either of the two time points investigated. The study showed that islet hormone changes accompany the early development of pancreatic tumors in the hamster pancreatic model. The hormone changes and apparent insulin resistance resemble the metabolic changes found in humans with pancreatic cancer.     

Scanning electron microscopic study of precancerous and cancerous pancreatic lesions induced by N-nitrosobis (2-oxopropyl) amine in Syrian golden hamsters

Sequential alteration of Syrian golden hamster pancreatic ducts and ductules was investigated by scanning electron microscope during and subsequent to 10 weekly subcutaneous injections of N-nitrosobis (2-oxopropyl) amine (BOP). By examining surface morphology of ductal cells and resin casts of the secretory branches arising from the common duct, a series of lesions ranging from slight derangement of the luminal dimensions and loss of cilia to marked projections of "finger-like" processes accompanied by pleomorphism at the cellular and microvilli levels and increase in numbers of goblet cells could be established. A ductal histogenesis is proposed on the basis of the present scanning electron microscopic and earlier light microscopic findings.     

Inhibition of pancreatic hepatocyte induction in hamsters treated sequentially with ethionine, a protein-free diet and then methionine by prior N-nitrosobis-(2-oxopropyl)amine administration

A 100% yield of pancreatic hepatocytes was induced in pancreas tissues of female hamsters treated with twice-repeated sequential administrations of DL-ethionine (ethionine) together with a protein-free diet and then L-methionine (methionine) for 10 weeks. The cells were also found in 40% of hamsters receiving 20 mg/kg body weight of the pancreatic carcinogen, N-nitrosobis(2-oxopropyl)amine (BOP) given twice at the peak of pancreatic regeneration stimulated by methionine after ethionine-induced cell damage. However, BOP at doses of 30, 70, and 100 mg/kg body weight administered before the occurrence of pancreatic regeneration dose-dependently inhibited their appearance, with reduction of the yield to 40%, 25%, and 8.3% respectively, and BOP per se did not induce any development of pancreatic hepatocytes. Stein iodine staining revealed bile pigments in the induced hamster pancreatic eosinophilic cell populations.     

Inhibition of Pancreatic Hepatocyte Induction in Hamsters Treated Sequentially with Ethionine, a Protein-free Diet and then Methionine by Prior N-nitrosobis-(2-oxopropyI)amine Administration

A 100% yield of pancreatic hepatocytes was induced in pancreas tissues of female hamsters treated with twice-repeated sequential administrations of DL-ethionine (ethionine) together with a protein-free diet and then L-methionine (methionine) for 10 weeks. The cells were also found in 40% of hamsters receiving 20mg/kg body weight of the pancreatic carcinogen, N nitrosobis(2-oxopropyl)amine (BOP) given twice at the peak of pancreatic regeneration stimulated by methionine after ethionine induced cell damage. However, BOP at doses of 30, 70, and 100 mg/kg body weight administered before the occurrence of pancreatic regeneration dose dependently inhibited their appearance, with reduction of the yield to 40%, 25%, and 8.3% respectively, and BOP per se did not induce any development of pancreatic hepatocytes. Stein iodine staining revealed bile pigments in the induced hamster pancreatic eosinophilic cell populations.     

Impact of Octreotide and SOM-230 on liver metastasis and hepatic lipidperoxidation in ductal pancreatic adenocarcinoma in Syrian Hamster

Octreotide is a somatostatin analogue binding on two receptor subtypes. In previous trials Octreotide showed inhibitory effects on tumour growth and liver metastasis in experimental pancreatic cancer. Thus we evaluated whether the new somatostatin analogue SOM-230 binding on 4 receptor subtypes has superior effects on carcinogenesis in pancreatic carcinoma. About 120 Syrian hamsters were randomised into six groups (n = 20): Gr.1: Aqua/Aqua, Gr.2: BOP/Aqua, Gr.3: Aqua/Octreotide, Gr.4: BOP/Octreotide, Gr.5: Aqua/SOM-230, Gr.6: BOP/SOM-230. Tumour groups 2,4,6 subcutaneously received 10 mg/kg body weight N-nitrosobis-2-oxopropylamin (BOP) weekly for 10 weeks, healthy control Gr.1,3,5 were given aqua. In the 17th week therapy started with Octreotide and SOM-230 for 16 weeks, after 32 weeks animals were sacrificed. Pancreas and liver were histopathologically analysed. Hepatic lipidperoxidation was determined by activities of antioxidative enzymes gluthation-peroxidase (GSH-Px) and superoxiddismutase (SOD) as well as concentration of thiobarbituric-acid reactive substances (TBARS). Incidence of liver metastases was 88.2% in Gr.2 (BOP/Aqua), it was decreased in Gr.4 (BOP/Octreo: 40%) and Gr.6 (BOP/SOM-230: 50%) (P < 0.05). Mean number/animal and mean-2-dimensional size of liver metastases did not differ between tumour groups. Comparing GSH-Px-activity in intrametastatic and extrametastatic hepatic tissue revealed a significant increase extrametastatically in Gr.2 (BOP/Aqua) and Gr.6 (BOP/SOM-230). SOD-activity in liver metastases was decreased in Gr.2 (1,801) (P < 0.05) versus Gr.4 (8,304) and Gr.6 (7,038). Intrametastatic TBARS concentration was increased in Gr.2 compared to Gr.4 (BOP/Octreotid) and Gr.6 (BOP/SOM-230) (P < 0.05). Octreotide and SOM-230 equally reduced liver metastasis in ductal pancreatic adenocarcinoma probably by a reduction of lipidperoxidation.     

Transplantation of pancreatic beta-cells prevents development of hypothalamic obesity in rats.

The present experiments have tested the hypothesis that ventromedial hypothalamic (VMH) lesions enhance insulin secretion by neural mechanisms. Rats were made diabetic by injecting streptozotocin to destroy their own pancreatic beta-cells. Subsequently, transplants of fetal pancreatic tissue were placed under the renal capsule. VMH lesions were placed in rats whose diabetes was cured with transplants as well as sham-transplanted animals. The animals were followed for 4 wk. The lesioned rats with pancreatic transplants gained no more weight than the sham-operated controls. There was no significant rise in insulin in the transplanted rats after VMH lesioning, but the VMH lesioned rats with intact pancreatic tissue showed the expected rise in insulin. Food intake rose 71% in the VMH lesioned rats with intact beta-cells, but only 23% in the VMH lesioned rats with transplants. Hypertrophy of the pancreatic islets was also observed in the VMH lesioned rats with an intact pancreas, but was not found in the VMH lesioned rats with a transplanted pancreas. Thus, transplantation of pancreatic tissue beneath the renal capsule of diabetic rats prevented the characteristic hyperphagia, hyperinsulinemia, and obesity in VMH lesioned rats whose pancreas was free from intact innervation. The results support the hypothesis that neural mediation of the rise in insulin is the primary factor in the development of hypothalamic obesity.     

Histogenesis and ultrastructure of pancreatic islet graft microvasculature. Evidence for graft revascularization by endothelial cells of host origin.

In previous studies we have demonstrated that syngeneic and xenogeneic pancreatic islet grafts are revascularized within a 10 to 14-day period after transplantation. With the combined use of intravital and electron microscopy, as well as immunohistochemistry using a set of species-specific or -crossreacting antibodies to endothelial cell antigens, we investigated 1) the origin of the endothelium of the newly formed capillaries in free pancreatic islet isografts (hamster-->hamster) and xenografts (rat-->hamster), and 2) the ultrastructural characteristics of these microvessels. Intravital microscopy demonstrated that newly formed microvessels grow from the vascular bed of the host muscle tissue into the islet grafts. Immunohistochemical analysis of host tissue and transplanted islets with antibodies against factor VIII (recognizing both hamster and rat factor VIII), bovine PECAM-1 (CD31; endoCAM, crossreacting with hamster but not rat PECAM-1), and rat ICAM-1 (CD54, non-crossreacting with hamster ICAM-1) showed that the transplanted rat islets were revascularized by endothelium of hamster (host) origin. At an ultrastructural level, the endothelial lining of the newly formed microvessels showed diaphragmatic fenestration, a characteristic feature of endothelial cells of pancreatic islets in situ. On the basis of these findings we suggest that pancreatic islet transplantation may take a unique position in the field of organ transplantation, since the generally proposed mechanisms of endothelial cell-dependent antigen recognition as a trigger of graft rejection may not be transferred to islet grafts, containing microvessels lined by endothelial cells of host origin.     

Distribution of acetylcholinesterase--and monoamine oxidase--positive neurons in pancreatic tissue transplant

Acetylcholinesterase-and monoamine oxidase-positive neuronal elements were investigated in embryonic pancreatic tissue fragments transplanted into the anterior eye-chamber of rats for 28, 77, and 135 d, using enzyme histochemical method. Amongst the components of the parenchymal tissue, only the ductal and islets cells survived. Monoamine oxidase (MAO)- and acetylcholinesterase (AChE)-positive neuronal cell bodies and fibres were found to be considerably many in the surviving and newly formed islets of Langerhans, in the wall and periphery of the tubules. Their topography with regards to these components is similar to that in normal tissue. In normal tissue, MAO-positive fibers abut the basal and lateral parts of acinar cells. AChE-positive neurons are most conspicuous in the islets and in the wall of pancreatic ducts.     

Uptake of tritiated D-mannoheptulose by liver, pancreatic exocrine and endocrine cells.

Tritiated D-mannoheptulose, a ketoheptose known to inhibit D-glucose metabolism in hepatocytes and pancreatic islets, but not so in pancreatic acinar cells, was injected intravenously in streptozotocin-induced diabetic mice transplanted under the kidney capsule with islets from control mice of the same strain. One hour after the injection of the tritiated heptose, the radioactive content was 5-8 times higher in the liver and transplanted islets than in the pancreatic gland. It is proposed that suitably radiolabelled D-mannoheptulose could be used to label preferentially the endocrine moiety of the pancreatic gland, e.g., in the perspective of its non-invasive imaging.     

Intraperitoneal transplantation of pancreatic anlagen

To determine whether embryonic pancreatic anlagen transplanted to an intraperitoneal site in adult hosts grow, differentiate, and function, we implanted pancreas from embryonic day (E) 12.5 Lewis rat embryos into the omentum of adult Lewis rats or C57Bl/6J mice. E12.5 pancreatic anlagen were relatively undifferentiated except for the presence of condensing tubuloacinar cords. By 2 weeks after implantation, pancreatic anlagen transplanted into rats had enlarged and differentiated such that islets of Langerhans that stained positive for insulin could be delineated. Continued differentiation, as reflected by the presence of "ductal" islets connected to the duct epithelium, was observed at 6 weeks after implantation. At 15 weeks after implantation, "mature" islets had separated from the ducts. Electron microscopy showed eccentric dense bodies within clear vacuoles consistent with insulin granules. Little or no acinar tissue was present in developed anlagen. Within 5 weeks of pancreatic anlagen transplantation, levels of glucose in rats rendered diabetic by an injection of streptozotocin were normalized compared with levels in nontransplanted diabetic controls. Rat pancreatic anlagen underwent growth and development in the peritoneum of C57Bl/61 mice that received costimulatory blocking agents but not in the absence of costimulatory blockade. We concluded that whole E12.5 pancreatic anlagen undergo growth, differentiation, and function after intraperitoneal placement. Implantation of the embryonic pancreas, a "cellular" transplant, is followed by selective differentiation of islet compared with acinar components.     

Experimental pancreatic carcinogenesis. I. Morphogenesis of pancreatic adenocarcinoma in the Syrian golden hamster induced by N-nitroso-bis(2-hydroxypropyl)amine.

In serial sacrifice experiment, outbred male Syrian golden hamsters were treated once weekly for life with subcutaneous injections of N-nitroso-bis(2-hydroxypropyl) amine (DIPN). The pancreas was examined by high resolution light (1-micro sections) and transmission electron microscopy. Early nonspecific changes in all pancreatic epithelial cellular elements were followed by a progressive proliferation of intra- and interlobular duct cells, with the development of multicentric foci of cystic and papillary cystic adenomas, intraductal carcinomas, and invasive ductal neoplasms. These observations were consistent with multistage morphogenesis of pancreatic adenocarcinoma of ductal origin.     

Expression of human tumor-associated antigens in pancreatic cancer induced in Syrian hamsters.

Our previous studies have shown that pancreatic cancer induced in Syrian hamsters by N-nitrosobis(2-oxopropyl)amine (BOP) shows remarkable similarities with the human disease in morphologic and biologic characteristics. Moreover, both human and hamster pancreatic cancer share expression of some tumor-associated antigens, such as those with blood group specificities, including A, B, H, Leb, Lex, and Ley. By examining other antigens commonly expressed in human pancreatic cancer, we have found that monoclonal antibodies CO17-1A (recognizing 17-1A antigen), OC 125 (recognizing CA 125 antigen), B72.3 (recognizing TAG-72 and DU-PAN-2 react with induced pancreatic cancer in a pattern similar to that seen in human pancreatic cancer. Remarkably, although the epitopes of the antigens recognized by these three antibodies are different, many tumor cells were reactive with all these antibodies. However, in contrast to the human cancer, none of these antigens were expressed in the normal hamster pancreatic tissue, except for 17-1A. However, all of these antigens were expressed in some hamster tissues showing the same cellular localization as pancreatic cancer cells and corresponded, to a great extent, with findings in human tissue. Expression of these antigens was diminished in vitro (cell culture) but was regained in vivo (homologous transplantation). The results emphasize the usefulness of this experimental model for studying some aspects of tissue antigenicity, particularly as it relates to pancreatic cancer.     

Revascularization and remodelling of pancreatic islets grafted under the kidney capsule

The revascularization and the structural changes resulting from interactions between the graft and the host were investigated in transplanted pancreatic islets under the kidney capsule. Islets were isolated from mice pancreata and transplanted in syngeneic diabetic animals. Graft-bearing kidneys were collected on different days post-transplant and processed for light microscopy, immunohistochemistry and transmission electron microscopy. A numerical analysis was performed in order to compare the percentage number of the different types of cells in native islets and at different time points after the transplant. Recipient animals reversed diabetes within 4 days. An intraperitoneal glucose tolerance test was performed to determine islet functionality under stressful conditions. During the initial few days post-transplant, the islets showed peculiar shapes and the graft tended to aggregate along the vessels. Starting at days 4-7 post-transplant, islets were revascularized from vessels connected to both the cortical and the capsular vascular network of the kidney. From day 7-14 post-transplant, the vessels progressively appeared more similar in features and size to those of in situ pancreatic islets. Both the percentage number of the different cell types and the distribution of Alpha, Beta and Delta cells inside the graft were significantly different as compared with intact islets, demonstrating quantitative and structural changes after the engraftment. No concomitant proliferation of Beta cells was detected using a bromodeoxyuridin staining method. Despite the fact that quick revascularization preserved a large mass of tissue, the remodelling process of the graft and the newly formed vascularization led to a different organization of the endocrine tissue as compared with intact in situ islets. This constitutes the morphological basis for alterations of the normal intercellular interactions and may explain the altered secretory cell function often observed in transplant.