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Site-Specific/Stable Radioiodination of 1,2-Pal-3-IPPA: An Agent for the Potential Clinical Evaluation of Pancreatic Insufficiency by Urine Analysis

Nuclear Medicine Group, Health and Safety Research Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee
Clinic for Nuclear Medicine, University of Bonn, Bonn, Germany

Correspondence: For correspondence or reprints contact: F.F. (Russ) Knapp, Jr., PhD, Group Leader, Nuclear Medicine, Building 3047, Oak Ridge National Laboratory, P.O. Box 2008, Oak Ridge, TN, 37831-6022.

ABSTRACT

To measure pancreatic lipase activity, we synthesized a triglyceride containing a radioiodinated fatty acid. The urinary excretion of radioactivity was measured in five rats following administration of the agent by feeding tube. We attached 15-phenylpentadecanoic acid (PPA) to position-3 of 1,2-dipalmitoyl-rac-glycerol (1,2-Pal) to form 1,2-Pal-3-PPA. The 1,2-Pal-3-IPPA (expected lipase substrate) was prepared by the thallation-iodide displacement method. In a dual-label study, the ¹²⁵I-1,2-Pal-3-IPPA triglyceride was administered with the ¹³¹I-IPPA free 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 (¹²⁵I, 30.31% + 4.32%; ¹³¹I, 35.0% + 7.29%), which Cochromatographed with hippuric acid by thin layer chromatography. Release of the acidic components from the conjugated excretory products by acid hydrolysis of the urine provided the radioactive addic 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 various gastrointestinal diseases.

FOOTNOTES

^* Current address: Department of Chemistry, University of Metz, Metz, France.