Free aminoacids in plasma and milk of Mexican rural lactating women

Objective. To determine the free amino acid pool in plasma and milk in Mexi can rural lactating women. Methods. Twenty-eight women with an age 24 +/- 5 .0 (+/- SD) years, weight 50 +/- 4.9 kg and height 148 +/- 4.8 cm were stud ied under metabolic balance conditions. Subjects were divided into five gro ups (three groups of lactation at 1(st), 3(rd) and 6(th) month, one post-we aning group and a control group of non pregnant, non lactating women). Amin oacid analyses of the diet and of plasma and milk samples were performed us ing an automated aminoacid analyzer. Results. Differences were observed bet ween the lactation groups and the other groups: aspartate increased at the 6(th) month (p < 0.05) while leucine, valine and isoleucine declined in the 3(rd) month (p < 0.05). In milk,valine, proline and taurine decreased at 6 months (p < 0.05), while serine and threonine raised at 3 months. Plasma l evels were > 4 fold greater than milk levels for branched chain amino acids and for the basic, aromatic and neutral aminoacids. In contrast, glutamate was 40 fold higher in milk than plasma and it was the predominant aminoaci d in the free pool of milk. Conclusions. Our results suggest that the metab olic use of aminoacids and the presence of specific aminoacid transport sys tems during lactation, contribute to specific concentrations of free aminoa cids in milk that were not associated with the pool of free aminoacids in p lasma.