Labeled plasma metabolites of L-methyl-hydrogen-3-methionine and L-methyl-carbon-14-methionine in the dog
The validity of the mathematical models that attempt to describe positron emission tomography (PET) images produced with (11CH3) methionine in terms of rates of local cerebral protein synthesis has yet to be established. A major objection to current models is that the use of methionine labeled at the methyl position results in the dispersal of the label among various methyl-accepting compounds that appear in the plasma and may then enter the brain. One approach to overcoming this problem has been the use of ''standard'' corrections for the activity contributed to plasma by labeled plasma protein and labeled serine. In order to determine the validity of this approach, the metabolic fate of labeled methionine was studied in six dogs. After injection with either (C3H3) methionine or (14CH3) methionine arterial blood was sampled. Plasma fractions containing protein were separated by fast gel filtration, counted with standard scintillation techniques, and their radioactivity was compared with total plasma radioactivity. Plasma was also separated by high-pressure liquid chromatography into methionine, serine, and nonmethionine or serine-containing fractions. These fractions were counted, and their radioactivity was compared with total plasma radioactivity. Labeled protein appeared in plasma about 20 minutes postinjection and then increased steadily. Labeled serine also appeared and reached a peak value of 9.4 +/- 2.1% of plasma activity at 40 minutes. Of greatest interest was the appearance in later plasma samples of increasing amounts of activity contained in nonserine low molecular weight metabolites of methionine. At 40 minutes, those metabolites made up 27 +/- 6.9% of total plasma activity.
- Research Organization:
- Johns Hopkins Medical Institutions, Baltimore, MD (USA)
- OSTI ID:
- 6270169
- Journal Information:
- Am. J. Physiol. Imag.; (United States), Journal Name: Am. J. Physiol. Imag.; (United States) Vol. 3:4; ISSN AJPIE
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
62 RADIOLOGY AND NUCLEAR MEDICINE
AMINO ACIDS
ANIMALS
BETA DECAY RADIOISOTOPES
BETA-PLUS DECAY RADIOISOTOPES
BIOLOGICAL MATERIALS
BLOOD
BLOOD PLASMA
BODY
BODY FLUIDS
BRAIN
CARBON 11
CARBON 14 COMPOUNDS
CARBON ISOTOPES
CARBOXYLIC ACIDS
CENTRAL NERVOUS SYSTEM
CHROMATOGRAPHY
COMPUTERIZED TOMOGRAPHY
COUNTING TECHNIQUES
DIAGNOSTIC TECHNIQUES
DOGS
DRUGS
EMISSION COMPUTED TOMOGRAPHY
EVEN-ODD NUCLEI
HYDROXY ACIDS
IMAGES
ISOTOPE APPLICATIONS
ISOTOPES
LABELLED COMPOUNDS
LIGHT NUCLEI
LIPOTROPIC FACTORS
LIQUID COLUMN CHROMATOGRAPHY
MAMMALS
MATERIALS
MATHEMATICAL MODELS
METABOLISM
METABOLITES
METHIONINE
MINUTES LIVING RADIOISOTOPES
NERVOUS SYSTEM
NUCLEI
ORGANIC ACIDS
ORGANIC COMPOUNDS
ORGANIC SULFUR COMPOUNDS
ORGANS
POSITRON COMPUTED TOMOGRAPHY
PROTEINS
RADIOISOTOPES
SCINTILLATION COUNTING
SEPARATION PROCESSES
SERINE
TESTING
TOMOGRAPHY
TRACER TECHNIQUES
TRITIUM COMPOUNDS
VALIDATION
VERTEBRATES