AJP - Gastrointestinal and Liver Physiology, Vol 254, Issue 4 631-G636, Copyright © 1988 by American Physiological Society
Effect of aging on intestinal absorption of aromatic amino acids in vitro in the rat
F. Navab and C. G. Winter
Department of Medicine, University of Arkansas for Medical Sciences, Little Rock 72205.
Whole-thickness everted jejunal rings were used to measure uptake of
L-tyrosine (L-Tyr), L-phenylalanine (L-Phe), and L-tryptophan (L-Trp) in
6-, 12-, and 24-mo-old rats. The rate of uptake of all three amino acids (1
mM) was significantly reduced after 20 min of incubation in 24-mo-old
compared with 6-mo-old rats. Results of influx (2 min) of 0.5-40.0 mM L-Phe
and L-Trp suggested an increased affinity but decreased capacity for the
transporter with age; these differences were significant for L-Trp (P less
than 0.05). Respective values for apparent Kt and Vmax were the following:
L-Phe 6-mo-old rats, 5.46 mM and 1.03 mumol.g-1.2 min-1; 24-mo-old rats,
2.54 mM and 0.51 mumol.g-1.2 min-1; L-Trp 6-mo-old rats, 5.09 mM and 0.38
mumol.g-1.2 min-1; 24-mo-old rats, 3.20 mM and 0.25 mumol.g-1.2 min-1.
Values for 12-mo-old rats fell in between the other two age groups.
