A new radiopharmaceutical for the cerebral dopaminergic presynaptic function: 6-radioiodinated L-meta-tyrosine

Geometric isomers of radioiodinated L-meta-tyrosine, 6-[I-125]iodo-and 4-[I -125]iodo-L-meta-tyrosine (6-I-L-mTyr, 4-I-L-mTyr) were separated by high-p erformance liquid chromatography. Both 6-I- and 4-I-L-mTyr had high energy- dependent brain accumulation. 6-I- and 4-I-r-mTyr were also metabolically s table and were rapidly excreted through the urine. 6-I-L-mTyr had a predile ction for the cerebral aromatic L-amino acid decarboxylase (DOPA decarboxyl ase), the final enzyme of dopamine biosynthesis, 6-Radioiodinated L-mTyr is a new radiopharmaceutical that can be both useful in assessing cerebral am ino acid transport mechanism and quantifying metabolically active DOPA deca rboxylase.