Vol. 284, Issue 1, R200-R207, January 2003
Cerebral leucine uptake and protein synthesis in the
near-term ovine fetus: relation to fetal behavioral state
Marie J.
Czikk,
John C.
Sweeley,
Jacobus H.
Homan,
J. Ross
Milley, and
Bryan S.
Richardson
Canadian Institute of Health Research Group in Fetal and
Neonatal Health and Development, Departments of Obstetrics and
Gynaecology and Physiology, Lawson Health Research Institute,
University of Western Ontario, London, Ontario, Canada N6A 4V2;
and Department of Pediatrics, Division of Neonatology, University
of Utah, Salt Lake City, Utah 84132
Behavioral/sleep state activity may
impact on synthetic processes within the brain, thus accounting for the
developmental change in such activity and suggesting a role in the
brain's growth and development. We have therefore determined the
cerebral uptake of leucine and [14C]leucine during
continuous tracer infusion as measures of leucine metabolism in
relation to behavioral state activity, as well as the regional flux of
leucine into brain tissue in the ovine fetus near term. The cerebral
fractional protein synthetic rate and the absolute protein synthetic
rate averaged ~20%/day and ~1 g/day, respectively, as measured for
the whole brain, which is considerably higher than anticipated protein
accretion and indicates a high rate of protein turnover with protein
synthesis closely linked to protein degradation. Measures of protein
synthesis were significantly higher in the pituitary gland, which may
be attributed to the active synthesis and export of peptide hormones
from this region. Cerebral leucine and [14C]leucine
uptakes averaged ~630 and ~1,000 nmol · 100 g
1 · min1, with the
latter higher than leucine unidirectional flux and thus supporting a
degree of leucine oxidation by the brain. Cerebral leucine metabolism
as studied was affected by behavioral state activity, with uptake
measurements for both leucine and [14C]leucine
significantly increased during the high-voltage
electrocortical/non-rapid eye movement state by 1.7-fold and
2.8-fold, respectively, indicating that protein synthesis and
degradation must also be increased at this time, and supporting a role
for behavioral state activity in the brain's growth and development.
brain development; leucine metabolism
