title: Fate of radioactive exocrine pancreatic proteins injected into the blood circulation of the rat. Tissue uptake and transepithelial excretion.
abstract: [35S]methionine or [35S]methionine-labeled exocrine pancreatic proteins were injected into the bloodstream of conscious rats. Samples of blood, urine, bile, and pancreatic juice were collected at varying intervals through 7 h. Injection of [35S]methionine resulted in the appearance of trichloroacetic acid--soluble radioactivity [( 35S]methionine) in bile and urine within 4 min and trichloroacetic acid-insoluble radioactivity in blood, bile, and pancreatic juice after 20 min. Analysis of these body fluids by two-dimensional isoelectric focusing/sodium dodecyl sulfate gel electrophoresis and fluorography indicated that rat serum, biliary, and pancreatic proteins were labeled, respectively. After the injection of [35S]methionine-labeled pancreatic proteins, half of the trichloroacetic acid-insoluble radioactivity disappeared from the serum in 10-15 min. Radioactive proteins appeared after 5 min in urine and bile, and, over the course of the experiment, accounted for 1%-2% and 0.3%-0.5% of the injected radioactivity, respectively. Analysis of individual radioactive proteins excreted into bile by two-dimensional isoelectric focusing/sodium dodecyl sulfate gel electrophoresis indicated preferential transhepatic transport of negatively charged pancreatic proteins. The majority of pancreatic proteins (approximately 97%) were taken up by a variety of body tissues, particularly kidney, liver, spleen, and lung. Trichloroacetic acid-soluble radioactivity, largely representing [35S]methionine, appeared sequentially in serum, urine, and bile within 2-12 min. At later experimental time points (greater than 60-90 min), radioactive rat serum, biliary, and pancreatic proteins appeared in blood, bile, and pancreatic juice, respectively. After the injection of 35S-labeled guinea pig pancreatic proteins into the blood circulation of the rat, trichloroacetic acid-insoluble radioactivity, observed in pancreatic juice after 60-90 min, exclusively represented rat exocrine pancreatic proteins as judged by the two-dimensional gel procedure. These studies indicate that pancreatic proteins are removed from the blood circulation by at least three separate pathways: (a) uptake and degradation by a variety of tissues in the body (approximately 97% of injected radioactivity), (b) excretion of intact proteins into urine (1%-2%), and (c) transport of intact proteins into bile (0.3%-0.5%). Transport of exocrine pancreatic proteins from the blood circulation to pancreatic juice could not be demonstrated.
mesh_terms: D000818:Animals; D001646:Bile / Q000378:metabolism; D001797:Blood Protein Electrophoresis; D007525:Isoelectric Focusing; D007700:Kinetics; D008297:Male; D008715:Methionine; D010179:Pancreas / Q000378:metabolism*; D010189:Pancreatic Juice / Q000378:metabolism; D011506:Proteins / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains; D013462:Sulfur Radioisotopes; D013997:Time Factors; D014018:Tissue Distribution
chemical_list: D011506:Proteins; D013462:Sulfur Radioisotopes; D008715:Methionine