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

Abstract

A number of environmental factors affecting the incorporation of ~-1eucine-l~C into brain proteins of newborn rats and guinea pigs under in uiuo conditions have been investigated. Reduction of ambient temperature from 35 to 22" results in a 35y0 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 O 2 concentrations below 10% in inspired air. Anoxia does not affect the entry of an inert amino acid, 14 C-a-aminoisobutyric acid, into brain substance under in viuo 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. SpecuZation 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.

Effect of Temperature on Fatty Acid Metabolism in Dissociated Cell Cultures of Developing Brain

“…s est. T h e EPG fraction was labeled more slowly than the CPG fraction, and the entry of radioactivity into noic acid (22 : 5), and docosahexaenoic acid (22 : 6), two leucine into brain proteins [8]. This effect is apparently the direct result of lowered body temperature, rather than being caused by energy depletion which accompanies thermogenesis.…”