Incorporation of Carbon From Glucose Into Cerebral Amino Acids, Proteins and Lipids, and Alterations During Recovery From Hypo‐glycaemia¹

Abstract— [U‐ 14 C]Glucose was given to dogs by intravenous infusion to maintain a fixed level of specific radioactivity of the plasma glucose. The time course of incorporation of 14 C into free amino acids, proteins and lipids of the cerebrum was observed for periods up to 2 h. Labelling of amino acids closely related to the tricarboxylic acid cycle increased progressively throughout the infusion, approaching specific radioactivities per μg‐atom of carbon equal to that of the plasma glucose. No significant dilution by unlabelled carbon entering the metabolic pathways was apparent. In dogs subjected to profound insulin hypoglycaemia, [U‐ 14 C]glucose mixed with unlabelled glucose was given to bring about recovery. The incorporation of 14 C into glutamate, glutamine and aspartate during a 40‐min period was greater than during a comparable period in control animals, whereas the incorporation into serine was reduced. When considered in relation to alterations in amino acid levels, the data suggest that during recovery from hypoglycaemia the rates of synthesis of amino acids related to the tricarboxylic acid cycle are increased. During the period of recovery the rates of incorporation of 14 C from glucose into proteins exceeded the pre‐insulin rates to a degree surpassing the increased incorporation into free amino acids. The labelling of the ganglioside, cerebroside‐sulphatide and cephalin fractions was also increased, The rates of incorporation into the lecithin‐sphin‐gomyelin and cholesterol fractions during recovery were the same as in the pre‐insulin period. Hypoglycaemia decreased the cerebral content of the phospholipid fractions; the lecithin‐sphingomyelin fraction returned toward normal during recovery, whereas the cephalins did not increase significantly. The electrographic patterns and the occurrence of convulsive activity are discussed, both in insulin hypoglycaemia and during recovery.