The kinetics of amino acid disappearance in the small intestine is related to the extent of amino acids absorbed in growing pigs.

This study evaluated the importance of correcting for amino acids (AAs) released into the hindgut on a measure of AA absorption kinetics and tested whether AA absorption kinetics are related to the extent of AA absorption using the growing pig as a model for humans. Thirty-six nine-week-old pigs (22.3 kg) received a diet containing whey protein as the sole protein source for eight days. Pigs received their last meal containing the indigestible marker titanium dioxide before being euthanized at 1, 2, 3, 4, 6, and 12 h post-feeding. The entire content of each gastrointestinal tract (GIT) region was collected to determine AAs released into the hindgut, and the kinetics and extent of AA absorption (uncorrected and corrected for AAs entering the hindgut). Amounts of AAs released into the hindgut increased over time (e.g., 33 and 180 mg of Glu for 4 and 6 h post-feeding). The corrected apparent amount of each AA absorbed from the GIT lumen after 4 h post-feeding was generally lower ( P ≤0.05) than the uncorrected counterpart. Differences in both the kinetics and extent of AA absorption were observed across AAs. For example, the time to reach half of the apparent AA absorption (T 50 ) was 1.5 and 3.4 h for Met and Arg respectively, whereas their extent of apparent absorption was 73 and 95%. Negative correlations between parameters related to kinetics and the extent of apparent absorption were observed (e.g., for T 50 r= -0.81; P <0.001). The kinetics of AA absorption is related to the extent of AA absorption.