Brain Uptake of Selenomethionine Se 75

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Abstract
Uptake of selenomethionine Se 75 after intravenous injection in rat was studied in brain, pancreas, plasma, muscle, scalp, and skull. Selenomethionine Se 75 enters rat brain by a rate-limited process with a free exchange at low blood concentrations. Acute preloading with intravenously administered nonradioactive L-methionine or L-phenylalanine results in a reduction of brain uptake of selenomethionine Se 75. Phenylalanine is a more effective inhibitor than methionine. Measurable inhibition of brain uptake of selenomethionine Se 75 is demonstrated at lower plasma levels of phenylalanine than commonly found in clinical phenylketonuria. Bidirectionality of carrier mediated exchange of selenomethionine Se 75 between blood and brain was demonstrated by ventriculocisternal perfusion studies in rabbits. The gamma emissions of selenomethionine Se 75 may be useful in clinical studies of blood brain barrier (BBB) penetration by amino acids which share the same carrier mechanism facilitating BBB passage of selenomethionine Se 75.