AMINO-ACID DISTRIBUTION AND METABOLISM IN PITUITARY-ADENOMAS USING POSITRON EMISSION TOMOGRAPHY WITH D-[C-11] METHIONINE AND L-[C-11] METHIONINE

Four patients with hormonally inactive pituitary adenomas were examined with positron emission tomography (PET) after injection, during different examinations, of L-[methyl-llC]methionine and D-[methyl-”C]methio-nine, respectively. After the rapid distribution phase, the enantiomer L-[“C]methionine, which is metabolically active, showed a considerable continuous irreversible trapping attributed to amino acid metabolism. The stereoisomer D-[nC]methionine, which does not participate in protein synthesis, showed a rapid distribution within the whole adenoma tissue, with a distribution space on the order of 100%. A minimal irreversible trapping was observed which could be explained by technical factors. It is concluded that PET using the two enantiomers allows a separation of passive distribution and metabolism, and that L-[“C]methionine can be used for in vivo quantitative studies of amino acid metabolism of pituitary adenomas. © 1987 Raven press, New York.