Amino acid metabolism by the fetal brain during normal and hypoglycemic conditions

Serum amino acid concentrations were quantitated using gas-liquid chromatography on blood samples drawn from fetal carotid artery, fetal sagittal vein, and a maternal peripheral artery under baseline conditions and during maternal and fetal hypoglycemia induced acutely by maternal insulin infusion. Serum concentrations of all amino acids were higher in the fetus than in the mother; in most cases, the letal levels were 2–4 times higher than the maternal. A similar pattern was observed during hypoglycemia, although there was a tendency for most maternal arterial serum amino acid concentrations to decline during hypoglycemia and for most fetal sagittal vein concentrations to increase. Positive arterio venous differences in amino acid concentration across the fetal brain were demonstrated for 14 of 15 amino acids. These differences decreased during hypoglycemia for 12 of these 14 amino acids, and for 7 of these amino acids the hypoglycemic arteriovenous differences actually became negative. The data suggest that acute fetomaternal hypoglycemia impairs net uptake of multiple amino acids by the fetal brain. The relationship, if any, between such impairment and the untoward clinical effects of severe perinatal and/or neonatal hypoglycemia must be established by further investigation.