Gluconeogenesis in infancy and childhood. I. A method for the study of the in vivo gluconeogenesis from alanine and glycerol.

The in vivo gluconeogenesis from alanine and glycerol in infants and children was studied by an isotope method, using 14C-labeled substates with subsequent separation of the radioactive compounds by thin-layer chromatography. Seven patients, aged 2 months to 2 years 11 months, with normal carbohydrate metabolism were studied. Trace amounts of [14C]alanine were injected intravenously in four fasting patients. The 14C moved quickly from alanine to lactate, with a peak activity in lactate obtained before 5 min. From 10 min on, the label disappeared rapidly from both. An equilibrium was established between alanine and lactate, displaced towards lactate. The peak activity in glucose was reached in 10-20 min, amounting to 10% of total injected activity. In one patient, who was also studied after a meal, the disappearance rate of alanine was reduced by 50%. Despite this reduction the appearance of label in lactate was increased, whereas the amount of label in glucose was much reduced. [14C]glycerol was injected intravenously in three fasting patients. In one patient, who received only a tracer dose of glycerol, 5 times more 14C appeared in glucose than in the patients studied with [14C]alanine. In two patients receiving a glycerol load together with the [14C]glycerol, the disappearance rate of glycerol was markedly reduced, as was the conversion of carbon to glucose and lactate.