A strategy for the study of cerebral amino acid transport using iodine-123-labeled amino acid radiopharmaceutical: 3-iodo-alpha-methyl-L-tyrosine.

We examined the brain accumulation of iodine-123-iodo-alpha-methyl-L-tyrosine (123I-L-AMT) in mice and rats. I-L-AMT showed high brain accumulation in mice, and in rats; rat brain uptake index exceeded that of 14C-L-tyrosine. The brain uptake index and the brain slice studies indicated the affinity of I-L-AMT for carrier-mediated and stereoselective active transport systems, respectively; both operating across the blood-brain barrier and cell membranes of the brain. The tissue homogenate analysis revealed that most of the accumulated radioactivity belonged to intact I-L-AMT, an indication of its stability. Thus, 123I-L-AMT appears to be a useful radiopharmaceutical for the selective measurement of cerebral amino acid transport.