Spontaneous hypertrophic foci of pancreatic acinar cells in CD rats

Nonproliferative and Proliferative Lesions of the Gastrointestinal Tract, Pancreas and Salivary Glands of the Rat and Mouse

The INHAND (International Harmonization of Nomenclature and Diagnostic Criteria for Lesions in Rats and Mice) project is a joint initiative of the Societies of Toxicologic Pathology from Europe (ESTP), Great Britain (BSTP), Japan (JSTP), and North America (STP) to develop an internationally accepted nomenclature and diagnostic criteria for nonproliferative and proliferative lesions in laboratory animals. The purpose of this publication is to provide a standardized nomenclature and diagnostic criteria for classifying lesions in the digestive system including the salivary glands and the exocrine pancreas of laboratory rats and mice. Most lesions are illustrated by color photomicrographs. The standardized nomenclature, the diagnostic criteria, and the photomicrographs are also available electronically on the Internet (http://www.goreni.org/). Sources of material included histopathology databases from government, academia, and industrial laboratories throughout the world. Content includes spontaneous and age related lesions as well as lesions induced by exposure to test items. Relevant infectious and parasitic lesions are included as well. A widely accepted and utilized international harmonization of nomenclature and diagnostic criteria for the digestive system will decrease misunderstandings among regulatory and scientific research organizations in different countries and provide a common language to increase and enrich international exchanges of information among toxicologists and pathologists.

Early indicators of exocrine pancreas carcinogenesis produced by non-genotoxic agents

In the past 40 years the incidence of pancreatic cancer in many Western countries had increased. Since no single factor responsible for the development of pancreatic cancer has been identified, it is believed that non-genotoxic factors may play an important role in the pathogenesis of this highly fatal form of cancer. Focal abnormalities of acinar cells, referred to as atypical acinar cell foci or nodules, occur spontaneously in rats and some other species. Their incidence increases with age from zero at birth to about 75% in 2-year-old rats. These spontaneous lesions have a phenotype that cannot be distinguished from the putative, atypical preneoplastic, acinar cell foci induced in rat pancreas by the carcinogen azaserine. Unsaturated fat (corn oil) has been found to increase the incidence of atypical acinar cell nodules and adenomas in the pancreas of non-carcinogen-treated rats without influencing the weight of the pancreas. Furthermore, unsaturated fat has a specific promoting effect on the growth potential of atypical acinar cell foci and nodules induced in rat pancreas by azaserine, resulting in an increase in the number and size of these lesions. Rats fed raw soya flour or trypsin inhibitors develop an enlarged pancreas as a result of hypertrophy and hyperplasia. They also develop acidophilic atypical acinar cell foci and nodules, adenomas and adenocarcinomas after being fed full-fat raw soya flour for 2 years. It may be concluded from the observations in rat pancreas that non-genotoxic compounds or conditions that enhance pancreatic growth may be classified as non-genotoxic pancreatic tumour promoters. The observations with corn oil, however, indicate that there may be non-genotoxic compounds that specifically enhance growth of spontaneous initiated atypical acinar cell foci without causing hyperplasia of the pancreas. The possible mechanisms whereby unsaturated fat and trypsin inhibitors exert their effects on exocrine pancreatic carcinogenesis are discussed.

Preneoplastic and neoplastic lesions in the pancreas of rats fed choline-devoid or choline-supplemented diets

Groups of male Fischer 344 rats were chronically fed semipurified choline-devoid or choline-supplemented diets, high in fat (15%), and containing or not containing 0.06% phenobarbital. Atypical acinar cell nodules were observed in the pancreas of the rats, irrespective of the diet fed, with incidences varying from 38% to 100% in the various groups. No consistent differential effects of the dietary treatments on the incidence and growth of the nodules were evident, even though the diameter of the nodules tended to be greater in some of the groups fed the basal choline-devoid diet. The vast majority of the nodules were of the acidophilic type. More advanced pancreatic acinar cell lesions were observed in a few of the rats. Since the rats were not exposed to a chemical carcinogen(s), development of the nodules and of the more advanced lesions, even in rats fed the control diets, was most likely due to evolution of endogenous (spontaneous) initiated pancreatic cells, promoted primarily by the feeding of semipurified diets with a high fat content.

Focal eosinophilic hypertrophic cells of the rat pancreas

Focal spontaneously occurring eosinophilic hypertrophic cells, histomorphologically resembling oncocytes and hepatocytes, were observed in the pancreas from 11 (0.3%) of 4,177 Sprague-Dawley rats, 3 to 26 months old. The age of these eleven rats ranged from 13 to 25 months. The incidence was not different between sexes. The altered cells were usually seen in the peri-insular area. Two types of foci, uniform and pleomorphic, were classified on the basis of uniformity of size of the altered cells within a focus. The origin and nature were not determined for the altered cells/foci reported in this study but they were not considered to be neoplastic.

Spontaneous basophilic hypertrophic foci of the parotid glands in rats and mice

Basophilic hypertrophic foci of the parotid glands characterized by focal hypertrophy and hyperchromasia of acinar cells was seen in Sprague-Dawley rats and Swiss mice with overall incidences of 4.8% (102/2,138) and 0.6% (4/723), respectively. In rats, the incidence increased significantly with age, but the size and number of the lesions per rat did not. Based on the similar incidence in both control and treated animals, lesions were considered to be spontaneous. Their morphology and growth pattern suggested that they were neither degenerative, necrotic, hyperplastic/preneoplastic, nor neoplastic, but, that they are a distinct pathologic entity of a nature not yet determined.

Effects of feeding partial and intermittent raw soya flour diets on the rat pancreas

Continuous administration of a diet consisting of raw soya flour produces pancreatic cancer in rats and sensitises the rat pancreas to the action of genotoxic carcinogens. We have therefore studied the effects of continuous feeding of diets containing lesser amounts of raw soya flour (5%, 25% and 50%) and feeding raw soya flour intermittently (2 days each week). The study has shown that a diet containing as little as 5% raw soya flour stimulates focal proliferation of the pancreatic acinar cells and sensitises to the action of azaserine. Similarly, intermittent feeding of raw soya flour induced focal proliferation of the acinar pancreas and, when 100% raw soya flour diet was fed for 2 days each week, resulted in the development of pancreatic cancer in some of the rats. We conclude that raw soya flour must be excluded from the diets of rats used in toxicological and carcinogenicity studies.

Enhancement of pancreatic carcinogenesis by raw soy protein isolate: quantitative rat model and nutritional considerations

Foods containing soybean products have been shown to modify the biochemical and physiological status of the pancreas of several species of experimental animals. Recently, these products have been implicated as a factor in the causation of pancreatic neoplasms. Extensive experimental studies into the possible mechanisms need to be undertaken. Experimental details of a rat/azaserine model for the study of pancreatic carcinogenesis are reviewed. Emphasis is given to the quantitative components of this model and the adaptation of this model to the two-stage (initiation-promotion) concept of carcinogenesis. Particular attention is devoted to considerations of the experimental diets. Application of these concepts to the study of the postinitiational effects of raw and heated soybean protein isolate with and without the addition of high levels of unsaturated fat were undertaken. The results indicate that raw soybean isolate enhanced the growth of azaserine-induced pancreatic foci; whereas, a high level of unsaturated fat had a minimal effect. The effects of the soybean isolate were abolished by heat treatments, but the effects of the unsaturated fat would not be expected to be abolished by similar treatment with heat.

Hypertrophic foci of pancreatic acinar cells in rats

A morphologically distinctive type of pancreatic acinar cell foci, different from hyperplastic nodules and adenomas, in rats has been recognized for two decades. The lesions have been observed to occur spontaneously and to be induced experimentally. They consist of enlarged acinar cells with abundant cytoplasm of altered staining characteristics and prominent nuclei. There is, however, a wide divergence of opinion among investigators regarding the nature of the lesions. As a result of different interpretations and classifications, many terms have been given to them. Based on morphologic characteristics, the author has designated the lesions as hypertrophic foci, a descriptive morphological term. The biologic significance with particular reference to age and the relationship with acinar cell neoplasia is discussed. Also included in the review are similar lesions in other rodent species.