Brain Uptake of Selenomethionine Se 75

Abstract

Brain uptake of selenomethionine Se 75 following intravenous injection was studied in nine subjects with phenylketonuria (PKU) and 12 matched mentally retarded controls. Brain content following injection was monitored continuously for 20 minutes using a gamma radiation detector sampling a fixed volume of brain. Uptake was expressed as ratio of head counts per minute divided by dose counts per minute per kilogram of patient. Brain uptake of selenomethionine Se 75 was reduced in the PKU group relative to the control group with a significance of better than 0.001. Reduction of brain uptake of this amino acid analog is compatible with saturation of the blood brain barrier carrier system for selenomethionine Se 75 by the high blood phenylalanine in PKU. Findings derived here by external counting are consistent with previous parallel animal studies in which serum phenylalanine concentrations were elevated by intravenous preloading.