SITE-SPECIFIC STABLE RADIOIODINATION OF 1,2-PAL-3-IPPA - AN AGENT FORTHE POTENTIAL CLINICAL-EVALUATION OF PANCREATIC INSUFFICIENCY BY URINE ANALYSIS

To measure pancreatic lipase activity, we synthesized a triglyceride c ontaining a radioiodinated fatty acid. The urinary excretion of radioa ctivity was measured in five rats following administration of the agen t by feeding tube. We attached 15-phenylpentadecanoic acid (PPA) to po sition-3 of 1,2-dipalmitoyl-rac-glycerol (1,2-Pal) to form 1,2-Pal-3-P PA. The 1,2-Pal-3-IPPA (expected lipase substrate) was prepared by the thallation-iodide displacement method. In a dual-label study, the I-1 25-1,2-Pal-3-IPPA triglyceride was administered with the I-125-IPPA fr ee acid to rats (n = 5) by oral gavage. Urine and feces were collected daily and the tissue distribution of both tracers was evaluated over a five-day period. A significant portion of the administered activity was excreted in 24 hr in the urine (I-125 30.31% + 4.32%; I-131, 35.0% + 7.290%), which cochromatographed with hippuric acid by thin layer c hromatography. Release of the acidic components from the conjugated ex cretory products by acid hydrolysis of the urine provided the radioact ive acidic metabolites. Analysis of the Folch extracts of fat samples demonstrated that the radioactive components cochromatographed in the triglyceride region. This agent appears useful for the evaluation of v arious gastrointestinal diseases.