期刊
AMERICAN JOURNAL OF PHYSIOLOGY-ENDOCRINOLOGY AND METABOLISM
卷 285, 期 2, 页码 E420-E426出版社
AMER PHYSIOLOGICAL SOC
DOI: 10.1152/ajpendo.00080.2003
关键词
amino acid metabolism; albumin synthesis; stable isotopes; urea
资金
- NCRR NIH HHS [M01-RR-00188-34] Funding Source: Medline
- NICHD NIH HHS [HD-3737857] Funding Source: Medline
- NIDDK NIH HHS [R01DK-55478] Funding Source: Medline
Little is known about amino acid ( AA) and protein metabolism in lactating women. We hypothesized: 1) AA sources other than the plasma acid pool provide substrate for milk protein synthesis in humans and 2) if albumin was one such source, then albumin fractional synthesis rate (FSR) is higher in the lactating women. To test these hypotheses, six healthy exclusively breast-feeding women [ 27 +/- 3 yr; body mass index (BMI) 26 +/- 2 kg/m(2)] between 6 wk and 3 mo postpartum and six healthy nonlactating women ( 28 +/- 2 yr; BMI 22 +/- 1 kg/m(2)) were studied two times, in random order, during 22 h fasting or 10 h of continuous feeding with a mixed nutrient drink. Protein metabolism was determined using [1-C-13] leucine and [N-15(2)] urea. In both the fed and fasted states, a significant portion of milk protein ( 20 +/- 5 and 31 +/- 6%, respectively) was derived from sources other than the plasma free AA pool. A 70% higher ( P < 0.02) FSR of albumin was observed in lactating women during feeding, suggesting that albumin is a likely source of AA for milk protein synthesis. We conclude that plasma free AA contribute only 70 - 80% of the substrate for milk protein synthesis in humans and that albumin may be a significant source of amino acids for the remainder.
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