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-[1-125]iodo-L-meta-tyrosine (6-I-L-mTyr, 4-I-L-mTyr) were separated by high-performance liquid chromatography . Both 6-I- and 4-I-L-mTyr had high energy-dependent brain accumulation. 6-I- and 4-I-L-mTyr were also metabolically stable and were rapidly excreted through the urine. 6-I-L-mTyr had a predilection for the cerebral aromatic L-amino acid decarboxylase (DOPA decarboxylase), the final enzyme of dopamine biosynthesis. 6-Radioiodinated L-mTyr is a new radiopharmaceutical that can be both useful in assessing cerebral amino acid transport mechanism and quantifying metabolically active DOPA decarboxylase.