Effect of aging on intestinal absorption of aromatic amino acids in vitro in the rat

¹ Departments of Medicine, Physiology, and Biochemistry, University of Arkansas for Medical Sciences and Veterans Administration Medical Center, Little Rock, Arkansas 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 < 0.05). Respective values for apparent K_t and V_max were the following: l-Phe 6-mo-old rats, 5.46 mM and 1.03 µmol·g^–1·2 min^–1; 24-mo-old rats, 2.54 mM and 0.51 µmol·g^–1·2 min^–1; l-Trp 6-mo-old rats, 5.09 mM and 0.38 µmol·g^–1·2 min^–1; 24-mo-old rats, 3.20 mM and 0.25 µmol·g^–1·2 min^–1. Values for 12-mo-old rats fell in between the other two age groups.

intestinal weight; intestinal length; Fischer rats; kinetics of uptake; Hofstee plot; everted jejunal rings; neurotransmitter precursors

Submitted on June 14, 1986
Accepted on November 9, 1987