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L-Methionine Uptake by Human Cerebral Cortex: Maturation from Infancy to Old Age

Departments of Radiology, Neurology, and Oncology, Johns Hopkins Hospital, Baltimore, Maryland
Laboratory of Neurosciences, National Institute on Aging, National Institutes of Health, Bethesda, Maryland
Loats Associates, Westminster, Maryland

Correspondence: For reprints contact: L. A. O'Tuama, MD, Room 3233, Bader 2, Division of Nuclear Medicine, The Children's Hospital, 300 Longwood Ave., Boston, MA 02115.

ABSTRACT

Age-associated changes in amino acid transport from blood to normal frontal cortex were studied using positron emission tomography (PET). Seventeen patients, 1.8–71 yr, were injected intravenously with tracer doses of [¹¹C] L-methionine and a baseline PET scan was obtained. To assess competitive inhibition of [¹¹C]L-methionine uptake, patients received either oral L-phenylalanine or an i.v. infusion of amino acids 1 hr before a second PET study. Uptake of [¹¹C]L-methionine by frontal cortex decreased seven-fold between 1.8 and 71 yr (r = –0.71; p < 0.05). Blood-to-brain transfer of [¹¹C]L-methionine, at 4.5 yr, exceeded mean adult values by more than five-fold. Competitive inhibition reduced L-methionine uptake in all patients older than 4.6 yr. These developmental changes parallel findings in animals. The neutral amino acid transport system may modulate human brain amino acid levels to meet changing developmental metabolic needs.

FOOTNOTES

* Current address: Children's Hospital, Boston, MA.

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