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

Abstract

Extract: A number of environmental factors affecting the incorporation of L-leucine-14C into brain proteins of newborn rats and guinea pigs under in vivo conditions have been investigated. Reduction of ambient temperature from 35 to 22° results in a 35% decrease in the incorporation of leucine into brain proteins in the newborn rat. Similar alterations do not affect incorporation rates in the newborn guinea pig.Graded reductions of the oxygen concentration of inspired air do not affect incorporation rates into brain proteins of the newborn rat until total anoxia is achieved. In contrast, reduction of incorporation of leucine into liver proteins occurs at O2 concentrations below 10% in inspired air.Anoxia does not affect the entry of an inert amino acid, 14C-α-aminoisobutyric acid, into brain substance under in vivo conditions. It is concluded that alteration of levels of radioactivity in free amino acid pools under similar circumstances is not attributable to structural damage of the vascular bed.Speculation: These data indicate that reduction of ambient temperature alters protein biosynthetic processes in the brain of the newborn animal. The effect appears to be produced by direct alteration of body temperature rather than by energy depletion accompanying thermogenesis. This finding leads to the consideration that prolonged neonatal hypothermia may decelerate brain development with resulting cerebral deficits at a later time. By contrast, the lack of effect of severe hypoxia upon incorporation of amino acids into brain proteins suggests that hypoxic episodes in the neonate may have relatively little effect upon growth of the brain during the newborn period.