Ultrastructural changes in the exocrine pancreas of experimental pancreatolithiasis in dogs.

Histological changes in the pancreas at an early stage of pancreatolithiasis were observed using a canine model in which obstruction was induced by partial ligation of the major pancreatic duct. Light micrographs demonstrated pancreatic lesions similar to those in humans. Electron micrographs revealed dilated lumens of small ducts and degenerated ductal cells 3 months after the ligation. These changes became more severe and appeared more often when the period of ligation was prolonged up to 1 yr. Acinar cells demonstrated dilation of the rough endoplasmic reticulum and the Golgi apparatus, swelling of the mitochondria, and increase in the number of prezymogen granules. Microfilamentous substance appeared in markedly dilated rough endoplasmic reticulum and in the intercellular space as acinar cell lesions progressed and the basal membrane became disrupted. The substance might be involved in calculous formation, the incidence of which reached a plateau after 6 months of ligation, coinciding with the peak in appearance of the substance.