Regional rates of cerebral protein synthesis measured with L-[1-11C]leucine and PET in conscious, young adult men:: normal values, variability, and reproducibility

We report regional rates of cerebral protein synthesis ( rCPS) measured with the fully quantitative L-[ 1- C-11] leucine positron emission tomography ( PET) method. The method accounts for the fraction (lambda) of unlabeled amino acids in the precursor pool for protein synthesis derived from arterial plasma; the remainder ( 1 - lambda) comes from tissue proteolysis. We determined rCPS and k in 18 regions and whole brain in 10 healthy men ( 21 to 24 years). Subjects underwent two 90- min dynamic PET studies with arterial blood sampling at least 2 weeks apart. Rates of cerebral protein synthesis varied regionally and ranged from 0.97 +/- 0.70 to 2.25 +/- 0.20nmol/ g per min. Values of rCPS were in good agreement between the two PET studies. Mean differences in rCPS between studies ranged from 9% in cortical regions to 15% in white matter. The k value was comparatively more uniform across regions, ranging from 0.63 +/- 0.03 to 0.79 +/- 0.02. Mean differences in k between studies were 2% to 8%. Intersubject variability in rCPS was on average 6% in cortical areas, 9% in subcortical regions, and 12% in white matter; intersubject variability in k was 2% to 8%. Our data indicate that in human subjects low variance and highly reproducible measures of rCPS can be made with the L-[ 1-C-11] leucine PET method.