Umbilical venous-arterial differences of plasma amino acids in humans at midpregnancy

The plasma levels of 20 free amino acids in the umbilical vein (UV) and the umbilical artery (UA) of seven newborns (20-24 weeks gestation) were measured at delivery. Seven (lys, val, leu, thr, his, ile, phe, and met) of the essential amino acids and six [ala, glu (NH2), arg, pro, 1/2 cys, and asp (NH2)] of the nonessential amino acids were shown to be significantly higher in UV than in UA. Among these amino acids, alanine showed the largest value for umbilical venous-arterial difference (UV-UA). Total plasma amino acid concentration was shown to be higher in the UV than in the UA. The general pattern of UV-UA for plasma amino acids in newborns studied here was proven to resemble closely that of premature births reported earlier.