Postnatal Changes in Protein Metabolism of Brain: I. Studies in Newborn Miniature Pigs at Varying Conceptual Ages

Abstract

ExtractT h e incorporation of L-phenylalanine-14C into protein of several brain areas and into liver of the miniature pig has been studied in viuo. A sequential decrease (approximately 50 %) in incorporation of labeled phenylalanine occurred during the first day of life in all brain regions ( fig. 1). There was no important difference in degree of incorporatn ioin the three brain regions examined. Labeling of liver protein was roughly threefold higher than in brain protein. A considerably smaller postnatal decrease of labeling of liver protein occurred in proportion to the total initial count.Premature delivery by hysterectomy a t two different conceptual ages resulted in a similar reduction of labeling of brain protein fractions, suggesting that birth rather than the conceptual age of the animal was the relevant factor ( figs. 2 and 3).Radioactivity in the trichloracetic acid-soluble fraction (free amino acids) of all brain areas increased during the first day of life, suggesting that the decreased incorporation of labeled amino acid was not a function of failure of the tracer to enter into brain substance (fig. 4).Expression of the radioactivity of protein in the brain regions as a function of radioactivity of liver protein established that while there is some postnatal decrease of incorporation into liver protein, there is a relatively greater decrease of incorporation into various brain regions (table I ) . Speculation

Postnatal Changes in Protein Metabolism of Brain. II. Effects of Alteration of Ambient Temperature and Gaseous Composition of Inspired Air

“…We have suggested that incorporation of tracers into the heterogeneous proteins of organ homogenates is best regarded as being analogous to the metabolic rate of whole organisms since it is a result of incorporation into numerous protein fractions existing in regional and subcellular locations [15]. A previous study of the labeling of subcellular fractions of brain proteins in vivo has revealed the highest rate of incorporation during 0.5-3 hr after injection to occur in the microso-ma1 protein fraction [5].…”

Growth and Development of the Fetal Rhesus Monkey (Macaca mulatta). II. Total Nitrogen, Protein, Lipid, Glycogen, and Water Composition of Major Organs

“…The rate of protein synthesis in fetal organs is generally higher than that seen in adult tissues [18,27]. As fetal organs mature functionally and structurally at differing rates, differences in their total nitrogen and protein content might be anticipated.…”