A New Radiopharmaceutical for the Cerebral Dopaminergic Presynaptic Function: 6-Radioiodinated l-meta-Tyrosine

Abstract

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-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.