LOCALIZATION AND CHARACTERIZATION OF SECRETIN BINDING-SITES EXPRESSED BY RAT BILE-DUCT EPITHELIUM

The goal of the present studies was to identify and characterize the site of secretin action in the liver. Sections of normal and bile duct-ligated rat livers were used for in vitro 125I-secretin receptor autoradiography. Saturable binding was observed in both normal and bile duct-ligated livers but was much greater in the bile duct-ligated preparations. Binding was limited to biliary epithelium and the increased secretin binding observed in the ligated livers correlated with the increase in ductular tissue. Saturable binding was inhibited in a dose-dependent fashion by increasing concentrations of nonradioactive secretin. Analysis of saturation binding showed that 125I-secretin binding was best fit by a one-site receptor model with a Kd of 5.3 ± 1.1 nmol/L. Glucagon, vasoactive intestinal polypeptide, gastric inhibitory polypeptide, growth hormone-releasing hormone, and cholecystokinin did not inhibit saturable 125I-secretin binding at concentrations of 1 pmol/L to 1 μmol/L. The authors conclude that high-affinity, specific secretin binding sites are present in rat intrahepatic biliary epithelium. When bile ducts are stimulated to proliferate by bile duct ligation, secretin binding is also increased. © 1992.