Protein Turnover in Brain of the Rat Fetus

Protein synthesis in vivo was studied in whole brain of rat fetuses using continuous intravenous infusion of L‐[U‐ 14 C]tyrosine into unrestrained pregnant rats at 19 and 21 days gestation. Protein degradation ( K D ) was calculated by subtracting fractional growth rate of brain protein ( K G ) from the fractional synthesis rate ( K s ). K s was high at both gestational ages (0.42 ± 0.03 days −1 at day 19, 0.47 ± 0.029 days −1 at 21 days), comparable to values previously reported for newborn rat cerebral hemispheres, and threefold higher than is seen in adult animals. K D was similar at both 19 and 21 days gestation (0.19‐0.24) and lower than that reported in neonatal rat brain using similar techniques. Protein accretion during the most rapid phase of brain growth (fetus) is accomplished by similar rates of protein synthesis, but decreased rates of degradation when compared with a slower growth phase (newborn). K D in the brain of the rapidly growing fetus is slightly higher than in adult cerebral hemispheres.