Radioactive compounds, N-iodo[
131I]acetyl-dl-tryptophan (II), 3, 5-diiodo[
131I]tyrosine (III), and p-iodo-(IV), m-iodo-(V), and o-iodo-pheny1alanine[
131I](VI), were synthesized and used in experimental animals. In isotopic exchange reactions of IV, V, and VI, the reaction velocities largely depended upon specific activity of inorganic radioactive iodine-131 used. IV, V, and VI showed selective accumlation in pancreas of mice and rats, showing possibility of their use as pancreas scanning agents. In comparison with radioactive selenomethionine[
75Se](I), IV showed higher pancreas/liver concentration ratio than I, when both were injected simultaneously into a mouse. Among three derivatives of iodo-phenylalanine, VI was demonstrated to give the highest pancreas/liver and pancreas/blood concentration ratios. It was also demonstrated that smaller administration dose of VI gave higher uptake into pancreas and liver. The accumulation of VI in pancreas was portrayed by autoradiogram of a mouse. It was found that this compound was also selectively taken into various kinds of tumor in rats and mice. However, the iodophenylalanine incorporated into pancreas or tumor was not utilized for protein synthesis, but remained in its original chemical form. In urine, a radioactive substance of another chemical form was found and its excretion rate was slower than that of original chemical form.
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