Plasma amino acid concentrations in newborn infants breast-fed ad libitum.

Plasma amino acid concentrations were measured in peripheral venous blood of 40 newborn infants breast-fed ad libitum. When these data are compared with amino acid concentrations of umbilical cord artery plasma, only lysine and threonine show a striking decrease after birth: the concentrations of hydroxyproline, asparagine, glutamine, proline, cystine, leucine, tyrosine, and ornithine significantly increase during the first days of life. The high-protein concentration of colostrum and transitional milk may explain this observation.