[Changes in the mouse pancreas after reopening the closed pancreatic duct: a qualitative and quantitative histologic study].

To understand histologic regeneration of deteriorated pancreas, pancreatic duct was clipped at 6 weeks of age in mice, the clip was removed 1 week after clipping, and the pancreas was histologically examined 1,2,3,5,7 and 14 days after removing the clip. For quantitative evaluation of the histologic changes, volume of the pancreatic parenchyma and volume densities, numerical densities, and relative total numbers of acinar cells and ductular cells in the pancreas were obtained by a stereological method using serial sections. In addition, the size and mitotic index was estimated for each cellular components. The pancreas was reduced to 18% of the normal after 1 week clipping. Exocrine acinar cells had degenerated and disappeared and the atrophied lobules were occupied by duct-like structures composed of cells like intercalated duct cells. The cells of duct-like structures showed occasional mitotic figures. Dilation of the ducts was noted. The histologic changes in the pancreas after removing the clip were classified with the two different groups (Group A and Group B). Group A pancreas showed regeneration of acinar cells, Group B pancreas showed no evidence of the regeneration. On the 2nd to 3rd days after removing the clip, in Group A pancreas, the lumen of the duct has been shrunken and acinar cells reappeared. Acinar cells were occasionally grouped at the terminal of the ducts. On the 7th day, the duct-like structures had almost disappeared, and exocrine acini were developed to show almost normal appearance of the lobules. The stereometry indicates that, after removing the clip from the duct, the total number of duct cells was decreased, while acinar cells rapidly increased until the 7th day when the increase became gradual, but eventually the recovery of the cell numbers was below the half of the normal range. The findings suggest that 1) duct-like structures in the atrophied pancreas proliferate from ductular cells in the pancreas, 2) reopening of the obstructed pancreatic duct induce regeneration of the acinar cells from the ductular cells, 3) regeneration of acinar cells complete of normal histology but does not recover the normal size of this organ, and 4) the stereological method is appreciated to evaluate correctly a quantitative cell dynamics in the whole organ.