TY - JOUR
T1 - Phenylalanine and tyrosine kinetics in young men throughout a continuous 24-h period, at a low phenylalanine intake
AU - Sánchez, Melchor
AU - El-Khoury, Antoine E.
AU - Castillo, Leticia
AU - Chapman, Thomas E.
AU - Young, Vernon R.
PY - 1995/3
Y1 - 1995/3
N2 - We determined the daily rates of whole-body phenylalanine oxidation (phe- Ox) and hydroxylation (phe-OH) in young men receiving [1-13C]phenylalanine and [2H2]tyrosine via primed, constant intravenous (n = 5) or oral (n = 7) infusions for a consecutive 24 h (12-h fast followed by 12-h fed period), and given a low-phenylalanine (21.9 mg · kg-1 · d-1), no-tyrosine, but otherwise adequate L-amino acid-based diet for 6 d before the tracer study. Estimates of the daily rates of phe-Ox and phe-OH were significantly higher (P < 0.001) for the subjects receiving the oral tracer, with estimates of phe-Ox obtained with the oral tracer during the 12-h fast period being close to those predicted from similar 24-h leucine kinetic studies (Am J Clin Nutr 1994;59:1000-11). There was generally poor agreement between the measured 24- h rates of phe-Ox and phe-OH compared with the daily rates as predicted from the last hour of the 12-h fast and 5th hour of feeding. From the 24-h data, daily phenylalanine balances were estimated to be positive with the intravenous-tracer protocol and negative with the oral-tracer group. Our results question the adequacy of current international recommendations for aromatic amino acid requirements in healthy adults.
AB - We determined the daily rates of whole-body phenylalanine oxidation (phe- Ox) and hydroxylation (phe-OH) in young men receiving [1-13C]phenylalanine and [2H2]tyrosine via primed, constant intravenous (n = 5) or oral (n = 7) infusions for a consecutive 24 h (12-h fast followed by 12-h fed period), and given a low-phenylalanine (21.9 mg · kg-1 · d-1), no-tyrosine, but otherwise adequate L-amino acid-based diet for 6 d before the tracer study. Estimates of the daily rates of phe-Ox and phe-OH were significantly higher (P < 0.001) for the subjects receiving the oral tracer, with estimates of phe-Ox obtained with the oral tracer during the 12-h fast period being close to those predicted from similar 24-h leucine kinetic studies (Am J Clin Nutr 1994;59:1000-11). There was generally poor agreement between the measured 24- h rates of phe-Ox and phe-OH compared with the daily rates as predicted from the last hour of the 12-h fast and 5th hour of feeding. From the 24-h data, daily phenylalanine balances were estimated to be positive with the intravenous-tracer protocol and negative with the oral-tracer group. Our results question the adequacy of current international recommendations for aromatic amino acid requirements in healthy adults.
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U2 - 10.1093/ajcn/61.3.555
DO - 10.1093/ajcn/61.3.555
M3 - Article
C2 - 7872220
AN - SCOPUS:0028817723
SN - 0002-9165
VL - 61
SP - 555
EP - 570
JO - American Journal of Clinical Nutrition
JF - American Journal of Clinical Nutrition
IS - 3
ER -