Ultrastructure of normal and neoplastic exocrine pancreas in the mummichog, Fundulus heteroclitus.

The ultrastructure of exocrine pancreatic neoplasms occurring in the mummichog, Fundulus heteroclitus, from a creosote-contaminated site in the Elizabeth River, Virginia, is described and related to nonneoplastic exocrine pancreas. Normal mummichog pancreas was an anastomosing tubular gland, with parenchymal cells organized as branched, anastomosing tubules around a central ductular system. The pancreatic ductular system consisted sequentially of terminal canalicular lumens lined by acinar cells, pancreatic preductules formed by an acinar and a centroductular cell, pancreatic ductules lined by 2 centroductular cells, and pancreatic ducts lined by cuboidal or columnar epithelial cells resting on a basal lamina and stromal sheath. Acinar cell adenomas retained the normal tubular organization and relationship between acinar and centroductular cells. Tumor cells exhibited nuclear pleomorphism but contained a full complement of normal zymogen granules and rough endoplasmic reticulum (RER). Some adenomas exhibited necrosis and cellular degeneration. Acinar cell carcinomas ranged from well to poorly differentiated. They exhibited loss of cell polarity, moderate to severe nuclear pleomorphism, extensive variation in size, shape, and number of zymogen granules, variability in RER content, and cellular degeneration. Acinar cell neoplasms in the mummichog were similar to those induced chemically in other fishes and certain mammals, suggesting that this fish population has been exposed to potent chemical carcinogens and that the species may be an effective indicator of polluted estuarine environments.