Fundamental Studies for the Development of Pancreas Scanning Agents

—Preparation of Radioactive Iodine-Labeled Amino Acids and Peptides, and Their Distribution—

Abstract

⁷⁵Se-Selenomethionine is often used for the isotope scanning of pancreas. However, it is desired to develop excellent pancreas scanning agents that give more specific distribution and less radiation hazards than the agent. Pancreas has a high ability to incorporate amino acids into its cells and to utilize the acids for the synthesis of proteins and enzymes. On the basis of this preferential uptake of amino acids, radioactive iodine-labeled amino acids and peptides, γ-¹³¹I-iodo-a-aminobutyric acid, N-2-¹³¹I-monoiodoacetyl-L- and D-leucines, L- and D-leucine 2-¹³¹I-iodoethyl esters, ¹²⁵I or ¹³¹I-labeled dipeptides, and insulin ¹²⁵I-A and ¹³¹I-B chains, were prepared and assayed for their distribution in mouse organs and Ehrlich ascites tumor cells. Radioactivity of these labeled compounds incorporated into pancreas was almost the same as that of liver and spleen, and considerably smaller than that of stomach, duodenum and kidney. Since a high incorporation into stomach was seen also after the administration of ¹²⁵I-sodium iodide, it was suggested that iodine ions were liberated in vivo from the labeled compounds within a short time.