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.     

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.     

Modification of pancreatic carcinogenesis in the hamster model. 3. Inhibitory effect of alloxan.

Alloxan, when given intravenously at a dose of 60 mg/kg body weight 2 hours prior to subcutaneous injection of the potent pancreatic carcinogen N-nitrosobis (2-oxopropyl) amine (BOP), inhibited the induction of hyperplastic and neoplastic pancreatic lesions in a statistically significant fashion (P less than 0.01). The number of lesions per animal affected was markedly less in these animals, compared with BOP-treated control animals. BOP administration 2 weeks after alloxan treatment, at which time pancreatic islet cell regeneration is considered completed, did not alter either the incidence or number of lesions. The results support our view that the pancreatic islet cells are the primary source of BOP metabolism. The concomitant inhibition of gallbladder tumors, but not of common duct neoplasms, in hamsters receiving BOP 2 hours after alloxan could indicate that alloxan's inhibitory effects on BOP carcinogenesis are not restricted to the pancreas.     

Inhibitory effect of 1α-hydroxyvitamin D3 on N-nitrosobis(2-oxopropyl)amine-induced cholangiocarcinogenesis in Syrian hamsters

Sixty-three male 5-week-old Syrian hamsters received the carcinogen N-nitrosobis(2-oxopropyl)amine (BOP) s.c. in 5 weekly injections (the first, 70 mg/kg body, and the remaining, 20mg/kg each). The hamsters that received BOP were given intragastric administration of 0.2 ml of medium chain triglyceride (MCT) with or without 0.04 μg of 1α-hydroxyvitamin D3 [1α(OH)D3] through a feeding tube for 12 weeks. Thus, 3 groups were assigned:Group 1;BOP alone (n＝20), Group 2;BOP＋MCT (n＝18) and Group 3;BOP＋1α(OH)D3 (n＝25). The mean body weight of Group 3 was lower than those of Groups 1 and 2 at the end of the experiment (p＜0.001,Tukey-Kramer HSD test). At the end of week 12, all surviving hamsters were put to sleep. The incidences of liver tumors were 80%, 72% and 32% in Groups 1, 2 and 3, respectively. The incidence of tumors in Group 3 was significantly lower than in Group 1 and Group 2 (p＜0.05, χ2-test). All tumors were cholangiocarcinoma. These results indicated that BOP-induced cholangiocarcinogenesis was suppressed by the supplemental administration of 1α(OH)D3.     

The role of pancreatic islets in experimental pancreatic carcinogenicity.

Our previous studies have suggested that the presence of intact islets is essential for the induction of pancreatic exocrine tumors in the Syrian hamster model. To validate this, we investigated the effect of the carcinogen, N-nitrosobis(2-oxo-propyl)amine (BOP) in hamsters, in which homologous isolated intact islets were transplanted into the submandibular gland (SMG). Freshly isolated pure islets from hamster donors were transplanted into the left SMG of 20 female host hamsters. Ten of these hamsters (group 1) received BOP (40 mg/kg) weekly for 3 weeks. Another 10 hamsters (group 2) were kept untreated. In groups 3 and 4 (10 hamsters each) the salt solution or isolated pancreatic ductal cells, respectively, was injected into the gland. In other groups (10 hamsters each) islets were transplanted into the peri-SMG connective tissue (group 5) or into the renal subcapsular space (group 6). Hamsters of group 1 (40 mg/kg, weekly for 3 weeks) as were group 7 hamsters, which served as BOP-treated controls. All BOP-treated hamsters developed pancreatic lesions. Similar hyperplastic and atypical ductal/ductular proliferation and in situ carcinoma were found in the SMG of many group 1 hamsters. No such lesions were found in the SMG, peri-SMG, or renal subcapsular space of the other groups. Islets appear to be involved in carcinogenicity of BOP. The mechanism is obscure.     

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.     

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.     

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.     

Intraductal proliferation in the pancreas and its relationship to human and experimental carcinogenesis

Summary In 21 patients who had undergone total pancreatectomy for pancreatic head carcinoma, the uninvolved pancreas was examined with regard to the type, incidence and regional distribution of duct epithelial proliferation. The results were compared with those in 37 operative specimens from patients with chronic pancreatitis, in 46 normal pancreases from autopsies and with findings in experimental pancreatic carcinogenesis.While the incidence of squamous metaplasia and non-papillary epithelial hypertrophy varied little in the different groups, papillary epithelial hyperplasia was found three times more often in cases of carcinoma, with associated mild duct obstruction. Atypical epithelial proliferation was only detected in the vicinity of carcinomas. Unequivocal transition from papillary hyperplasia to atypical proliferation was not observed. In hamsters treated with dihydroxy-di-n-propylnitrosamine (DHPN) for induction of pancreatic duct carcinomas, the early duct lesions closely resembled atypical epithelial proliferation of human pancreas.It is concluded that (1) papillary epithelial hyperplasia is probably only indicative of early duct obstruction and/or a general neoplastic stimulus, (2) intraductal epithelial proliferation with atypia is a true precursor of duct carcinoma, and (3) chronic pancreatitis lacks atypical duct lesions.     

Involvement of inflammatory factors in pancreatic carcinogenesis and preventive effects of anti-inflammatory agents

Chronic inflammation is known to be a risk for many cancers, including pancreatic cancer. Heavy alcohol drinking and cigarette smoking are major causes of pancreatitis, and epidemiological studies have shown that smoking and chronic pancreatitis are risk factors for pancreatic cancer. Meanwhile, inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2) are elevated in pancreatitis and pancreatic cancer tissues in humans and in animal models. Selective inhibitors of iNOS and COX-2 suppress pancreatic cancer development in a chemical carcinogenesis model of hamsters treated with N-nitrosobis(2-oxopropyl)amine (BOP). In addition, hyperlipidemia, obesity, and type II diabetes are also suggested to be associated with chronic inflammation in the pancreas and involved in pancreatic cancer development. We have shown that a high-fat diet increased pancreatic cancer development in BOP-treated hamsters, along with aggravation of hyperlipidemia, severe fatty infiltration, and increased expression of adipokines and inflammatory factors in the pancreas. Of note, fatty pancreas has been observed in obese and/or diabetic cases in humans. Preventive effects of anti-hyperlipidemic/anti-diabetic agents on pancreatic cancer have also been shown in humans and animals. Taking this evidence into consideration, modulation of inflammatory factors by anti-inflammatory agents will provide useful data for prevention of pancreatic cancer.     

Effect of cigarette smoke on mutagenic activation of environmental carcinogens by cytochrome P450 2A8 and inactivation by glucuronidation in hamster liver

To elucidate the mechanism underlying suppression of N-nitrosobis(2-oxopropyl)amine (BOP)-induced hamster pancreatic carcinogenesis by cigarette smoke (CS), hepatic levels of microsomal cytochrome P450 (CYP) enzymes, mutagenic activation of environmental carcinogens and three types of uridine diphosphate-glucuronyltransferase (UDPGT) and sulphotransferase (ST) activities were assayed in male Syrian golden hamsters and F344 rats exposed to CS. Immunoblot analyses of microsomal CYP proteins revealed induction of constitutive CYP1A2 (2.6-fold increase) and 2A8 (4.0-fold increase) and induction of CYP1A1 and constitutive CYP1A2 (3.9-fold increase) in rats following exposure to CS for 4 weeks using a Hamburg type II smoking machine. CS exposure enhanced mutagenicities of four heterocyclic amines in the presence of liver S9 in both species, whereas the mutagenicities of aflatoxin B(1) (AFB(1)), 2-amino-3-methyl-9H-pyrido[2,3-b]indole (MeAαC) and 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) were significantly increased by CS in hamsters but not in rats. However, no CS-induced alterations in the mutagenic activities of other carcinogens, including BOP and other pancreatic carcinogens, were observed in either species. Application of several CYP inhibitors revealed that the mutagenic activities of MeAαC, AFB(1) and NNK in the hamster liver S9 were partly associated with CYP2A8, whereas those of the three pancreatic carcinogens were selectively associated with CYP2B. CS enhanced UDPGT activities towards 4-nitrophenol (4-NP) (1.9- to 2.0-fold) but did not affect those of bilirubin, testosterone UDPGTs and three STs in both species. Together with the previous findings that BOP does not induce tumourigenesis in rats and that the glucuronidation of β-oxypropylnitrosamines is higher in rats than in hamsters, suppression of BOP-induced pancreatic carcinogenesis by CS might be attributed to increased detoxification by 4-NP UDPGT and not decreased CYP2B activation. This is the first demonstration of the induction of CYP2A protein by CS; CYP2A protein polymorphisms have been associated with oral and pulmonary carcinogenesis in smokers.     

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.     

Evidence for platelet-activating factor as a late-phase mediator of chronic pancreatitis in the rat.

The role of platelet-activating factor (PAF) as a mediator of pancreatic inflammation was examined in the rat pancreatic duct ligation model of obstructive pancreatitis. Pancreatic generation of PAF, as measured by bioassay (ie, platelet [3H]serotonin secretion), was determined at various times after induction of inflammation. Tissue levels of PAF in the normal pancreas averaged 600 +/- 49 pg/g, but PAF was not detectable during the initial 24 hours of pancreatitis, a time when the inflammatory reaction would be considered acute, that is, during the period of maximal serum amylase release and the development of interstitial edema. However a substantial increase in pancreatic PAF levels (12 times control levels) was observed 7 to 14 days after duct ligation during the late-phase response interval similar to the situation characteristic of chronic pancreatitis in which parenchymal atrophy, fibrosis, and pancreatic insufficiency evolve. One week after duct ligation when PAF levels peaked, an evaluation was made of the effects of PAF antagonists (BN52021 and WEB2170) on pancreatic lesions using Evan's blue extravasation, pancreatic myeloperoxidase (MPO) activity, and acid phosphatase activity in peritoneal lavage fluid. BN52021 or WEB2170 treatment was shown to reduce pancreatic damage and inflammation significantly. Long-term in vivo administration of exogenous PAF (20 micrograms/kg/hr for 7 days) exhibited a reduction of [3H]thymidine uptake into and amylase release from pancreatic acini in vitro. Our observations 1) that pancreatic PAF levels increased significantly during the chronic phase of obstructive pancreatitis induced by duct ligation; 2) that inhibition of the action of PAF, through specific receptor antagonism, caused an attenuation of pancreatic lesions; and 3) that chronic administration of PAF resulted in decreased pancreatic regeneration and exocrine function are consistent with a pivotal role for PAF as a late-phase inflammatory mediator in chronic pancreatitis in rats.     

Anatomical study of the pancreas in the house musk shrew (Suncus murinus), with special reference to the blood supply and innervation

To examine the macroscopic structure, blood supply, and innervation of the pancreas in the house musk shrew (Suncus murinus), we performed gross anatomical dissection and whole-mount immunostaining of the autonomic nerve of Suncus pancreases based on neurofilament protein (NFP) immunoreactivity. The adult Suncus pancreas is clearly separated into right and left lobes that are not fused. The right lobe of the Suncus pancreas is located in the dorsum of the duodenum and to the right of the common bile duct independently. The right lobe is supplied by branches of the superior mesenteric artery, and is innervated by branches that originate from the superior mesenteric plexus and run along the arterial branches of the superior mesenteric artery. The left lobe occupies 9/10 of the entire pancreas and is located to the left of the common bile duct. It is supplied mainly by branches of the splenic and common hepatic arteries, and is innervated by branches that originate from the celiac plexus and run along the splenic and common hepatic arteries. According to previous studies on the blood supply and innervation of the human pancreas, the right and left lobes of the Suncus pancreas correspond to the pancreatic parts derived from the ventral and dorsal pancreatic buds. The current results suggest that the Suncus pancreas is a suitable experimental model for studying the development of the human pancreas.     

Long-term culture and immortalization of epithelial cells from normal adult human pancreatic ducts transfected by the E6E7 gene of human papilloma virus 16.

Pancreatic cancer is one of the most lethal cancers in humans. The majority of these cancers arise from the pancreatic duct epithelium. Research into the pathogenesis of pancreatic carcinoma has largely relied on animal models. In vitro models of pancreatic carcinogenesis using propagable cultured epithelial cells derived from the pancreatic ducts of rats and hamsters have been described. A human model, however, has been nonexistent due to the unavailability of propagable cultured duct epithelial cells derived from normal human pancreas. We report here a reproducible method for the long-term culture of pancreatic duct epithelial cells derived from normal and benign adult human pancreata by infection with a retrovirus containing the E6 and E7 genes of the human papilloma virus 16. One of these cell lines has become immortal and has propagated continuously for more than 20 passages. They remain anchorage dependent in their growth and nontumorigenic in nude mice. These cell lines and the methodology described here to establish them may provide new avenues for in vitro studies of the roles played by duct epithelium in human pancreatic diseases and cancers.     

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.     

Effect of d,l-ethionine administration on the histomorphology of canine pancreatic acinar and β-cells

d,l-Ethionine produces pancreatic exocrine necrosis and islet proliferation in hamsters and dogs. As a first step in examining whether induction of islet proliferation has therapeutic applications in animals with exhausted or destroyed insulin-producing beta-cells, we studied pancreatic pathological alterations after intravenous administration of d,l-ethionine in normal dogs. Histomorphological changes in pancreatic acinar cells and beta-cells were assessed in three groups of six clinically normal crossbred dogs administered d,l-ethionine (100 mg/ kg) intravenously three times a week for two weeks. Six additional dogs served as untreated controls. Group I was euthanased and necropsied on day 15 (72 hours after the final dose of ethionine). Groups II and III were euthanased on days 29 and 43 respectively. Severe acinar destruction occurred resulting in significant (p < 0.001) shrinkage of the pancreas in all groups. Although there was variability in histomorphology within groups, pancreases of group I generally exhibited widespread loss of pancreatic acinar structure. Remaining acinar cells were difficult to discern from other cell types within lobules and were surrounded by infiltrates, predominantly of lymphocytes. Partial acinar cellular regeneration had occurred by day 29, but was still incomplete at day 43. Immunohistochemistry suggested that the effect of d,l-ethionine administration on the histomorphology of beta-cells in the left lobe was minimal; however, morphometry demonstrated a significant (p < 0.05) increase in the number of individual beta-cells in groups II and III, and clusters of 2-10, 10-20 and 20+ cells in Group II. It is probable that the apparent increase in the number of individual and other beta-cell arrangements observed in some groups resulted primarily from alterations in the exocrine tissue, although some beta-cell hyperplasia cannot be excluded completely.     

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.