RESUMO
Prefeeding and sequential postprandial plasma amino acid concentrations were measured in 31 healthy preterm infants with gestational ages between 33 and 37 weeks at the ages of 4 to 12 days, to characterize changes after quantitatively and qualitatively different protein loads. All infants had previously been fed with human milk. The infants received a normal feed of pooled human milk (true protein 0.8 gm/dl) or of adapted or nonadapted milk formula (protein 1.5 gm/dl) from a bottle. The concentrations of all essential and several nonessential amino acids, including arginine and ornithine, rose sharply in plasma. Glycine decreased, and alanine increased slowly. Postprandial alterations in plasma total amino acids seemed to reflect the protein content of the different milks. In preterm infants, fed at three- to four-hour intervals, plasma amino acid concentrations fluctuate continuously. Thus in long-term studies and in screening, samples should be taken immediately before feeds. Postprandial plasma amino acid measurements may prove to be a useful means for testing the infant's ability to handle the protein or individual amino acid loads in various feeds.
Assuntos
Aminoácidos/sangue , Alimentação com Mamadeira , Alimentos Infantis , Recém-Nascido Prematuro , Leite Humano , Aminoácidos/análise , Humanos , Alimentos Infantis/análise , Recém-Nascido , Proteínas do Leite/análise , Leite Humano/análiseRESUMO
Well, appropriate-for-gestational age, low-birth-weight infants weighing 2,100 gm or less were divided into three gestational age groups and assigned randomly within each age group to one of five feeding regimens: pooled human milk; formula 1 (F1) = 1.5gm/dl protein, 60 parts bovine whey proteins: 40 parts bovine caseins; F2 = 3.0 gm/dl, 60:40; F3 = 1.5 gm/dl, 18:82; F4=3.0 gm/dl, 18:82. Plasma and urine concentrations of methionine and of cystathionine were higher in the infants fed F1 to F4 than in the infants fed BM. The plasma cystine concentrations of infants fed F2 (which had a cystine content at least twice that of any of the other formulas) were significantly higher than those of infants fed BM. Plasma taurine concentrations of infants fed F1 or F4, which were virtually devoid of taurine, decreased steadily during the course of study becoming lower than those of infants fed BM. Urine taurine concentrations of infants fed F1, F3, or F4 (but not F2 which had more taurine than F1, F3, or F4) were lower than those of infants fed BM. These results provide further evidence for the limited capacity of the preterm human infant to convert methionine to cystine, owing to delayed maturation of cytathionase, and suggest a limited capacity to convert cystine to taurine. The latter suggestion is consistent with low human hepatic cysteinesulfinic acid decarboxylase activity 0.26 (fetal) and 0.32 (adult) nmoles/mg protein/hour vs 468 in rat liver.
Assuntos
Aminoácidos Sulfúricos/metabolismo , Recém-Nascido de Baixo Peso , Proteínas do Leite/análise , Aminoácidos Sulfúricos/sangue , Aminoácidos Sulfúricos/urina , Animais , Bovinos , Cistationina/metabolismo , Cistina/metabolismo , Humanos , Fenômenos Fisiológicos da Nutrição do Lactente , Recém-Nascido , Metionina/metabolismo , Necessidades Nutricionais , Taurina/metabolismoRESUMO
Well, appropriate-for-gestational age, low-birth-weight infants were divided into three gestational age groups and assigned randomly within each age group to one of five feeding regimens: pooled human milk (BM); formula 1 (F1) = 1.5 gm/dl protein, 60 parts bovine whey proteins: 40 parts bovine caseins; F2 = 3.0 gm/dl, 60:40; F3 = 1.5 gm/dl, 18:82; F4 = 3.0 gm/dl, 18:82. Plasma and urine concentrations of tyrosine and phenylalanine were far higher in the infants fed F1 to F4, especially F2 and F4, than in the infants fed BM. These findings offer further evidence for the limited capacity of the low-birth-weight infant to catabolize tyrosine. Infants fed F3 had significantly higher plasma tyrosine concentrations than infants fed F1, and those fed F4 had higher concentrations than those fed F2. Thus, increased plasma tyrosine concentrations in low-birth-weight infants are related directly both to the quantity and to the quality of the protein in their diets.