The tight junction of pancreatic exocrine cells is a morphometrically dynamic structure altered by intraductal hypertension

The tight junction of pancreatic exocrine cells is thought to regulate para cellular permeability, and is a possible reflux route of pancreatic juice i nto the blood flow. Morphological changes in the tight junction of canine p ancreatic acinar cells following intraductal hypertension and secretin stim ulation were morphometrically analyzed to obtain evidence of the control of the paracellular reflux. Pancreatic tissues obtained from 25 dogs after in traductal hypertension, 3 dogs after secretin stimulation, and 5 control do gs were studied. Intraductal pressure was either 20cmH2O, 30cmH2O, or 40cmH 2O. Freeze fracture replicas of these pancreatic tissues were observed by e lectron microscopy. Tight junctions were classified into six morphometric t ypes. Reticular type, parallel type, and mixed type comprised the common ty pes predominantly found in all groups, and three special types were found, infrequently, only after intraductal hypertension. The percentages of the c ommon types were significantly different between the groups. The areas of t he tight junctions, and other morphometric parameters, were significantly l ess after 20cmH2O intraductal hypertension and secretin stimulation than in the controls. However, these findings after 30cmH2O or 40cmH2O intraductal hypertension did not differ from those in the controls. The areas of the t hree special types of tight junctions were larger than those of the common types. These results suggest that the tight junction of pancreatic exocrine cells is a morphologically dynamic structure that is altered by the extent of intraductal hypertension, and support the hypothesis that paracellular permeability is the mechanism of the reflux of pancreatic juice.