ULTRASTRUCTURE OF NORMAL AND NEOPLASTIC EXOCRINE PANCREAS IN THE MUMMICHOG, FUNDULUS-HETEROCLITUS

The ultrastructure of exocrine pancreatic neoplasms occurring in the m ummichog, Fundulus heteroclitus, from a creosote-contaminated site in the Elizabeth River, Virginia, is described and related to nonneoplast ic exocrine pancreas. Normal mummichog pancreas was an anastomosing tu bular gland, with parenchymal cells organized as branched, anastomosin g tubules around a central ductular system. The pancreatic ductular sy stem consisted sequentially of terminal canalicular lumens lined by ac inar cells, pancreatic preductules formed by an acinar and a centroduc tular cell, pancreatic ductules lined by 2 centroductular cells, and p ancreatic ducts lined by cuboidal or columnar epithelial cells resting on a basal lamina and stromal sheath. Acinar cell adenomas retained t he normal tubular organization and relationship between acinar and cen troductular cells. Tumor cells exhibited nuclear pleomorphism but cont ained a full complement of normal zymogen granules and rough endoplasm ic reticulum (RER). Some adenomas exhibited necrosis and cellular dege neration. Acinar cell carcinomas ranged from well to poorly differenti ated. They exhibited loss of cell polarity, moderate to severe nuclear pleomorphism, extensive variation in size, shape, and number of zymog en granules, variability in RER content, and cellular degeneration. Ac inar cell neoplasms in the mummichog were similar to those induced che mically in other fishes and certain mammals, suggesting that this fish population has been exposed to potent chemical carcinogens and that t he species may be an effective indicator of polluted estuarine environ ments.