Effects of bile salts on permeability and morphology of main pancreatic duct in cats.

We studied the changes in permeability and morphology in the main pancreatic duct of cats after exposure of the duct to specific bile salts. Cats were anesthetized and the main pancreatic duct was cannulated in the tail and head of the pancreas. The duct was perfused with sodium cholate (1, 1.5, 2, 15 mM) or sodium glycodeoxycholate (1, 2, 15 mM) for 60 min at pressures which never exceeded 20 cm water. Then the duct was perfused with fluorescein-tagged dextran molecules of specific size (3000, 20,000, or 40,000 daltons). Recovery of the dextran from portal venous blood indicated that the duct was permeable to that particular dextran. Normally the ducts were impermeable to even the 3000-dalton dextran, and perfusion with either 1 mM cholate or glycodeoxycholate did not change this. However, perfusion with either bile salt at concentrations above 1 mM progressively increased duct permeability. At this highest bile salt concentrations used, the ducts became permeable to molecules as large as 20,000 daltons. Morphologic changes paralleled the changes in permeability. Control animals had pancreatic ducts whose ultrastructure was indistinguishable from normal. Perfusion of the ducts with low concentrations of bile salt for up to 60 min resulted only in a loss of microvilli from the cell surface and an increase in cytoplasmic phagolysosomes. Perfusion with higher concentrations of bile salt for 5-60 min induced progressively severe alterations. These included disruption of the tight junctions and the swelling of intercellular spaces between the duct cells, flattening of the duct epithelium, and eventual cell loss which left a break in the epithelial lining of the duct. These studies indicate that the pancreatic duct in cats, exposed to specific bile salts at physiological concentrations and pressures, undergoes marked structural alterations. The duct becomes permeable to molecules at least as large as 20,000 daltons, whereas it is normally impermeable to molecules as small as 3000 daltons.