The tight junction of main pancreatic duct epithelial cells is a morphometrically dynamic structure altered by intraductal hypertension.

Intercellular tight junctions play a role in the reflux of the exocrine pancreatic juice. Tight junctions of the main pancreatic duct were electron-microscopically compared between dogs with intraductal hypertension and controls, using a freeze-fracture technique and morphometrical analysis. Intraductal hypertension was created in seven dogs. Intraductal pressure was 20 cm H(2)O in two dogs, 30 cm H(2)O in two dogs, and 40 cm H(2)O in three dogs. Two dogs were killed as a control without any procedures. Freeze-fracture replicas were observed with an electron microscope. Tight junctions found in the replicas were morphometrically analyzed regarding the complexity, depth of strands, number of strands, and number of anastomoses. Parallel type and reticular type were recognized as two types of tight-junction complexity. The number of strands, the maximum and minimum depths, and the number of anastomoses were significantly higher in the reticular type than in the parallel type. The parallel type was predominant in the intraductal hypertension group and controls, and the parallel type was increased in the dogs with 20 cm H(2)O intraductal pressure. Morphometrical comparison between the intraductal hypertension groups and controls showed that the number of strands, the number of anastomoses, and the minimum and maximum depths of strands were significantly decreased only in the dogs with 20 cm H(2)O intraductal pressure. Intraductal hypertension may affect paracellular permeability through alterations in the number of strands and complexity in tight junctions of the main pancreatic duct epithelial cells.