Amino acid (AA) transporter proteins are responsible for the movement of amino acids
in and out of cells. Aminopeptidase cleaves AAs from the N-terminus of polypeptides
making them available for transport, while PepT1 is a di- and tripeptide transporter.
In the intestine, these proteins are present on the brush border and basolateral membranes
of enterocytes, and are essential for the uptake of AAs into enterocytes and their
release into circulation. The purpose of this study was to determine the level of
transcription of these genes after hatch in 3 regions of the small intestine, the
ceca, and liver. Heritage broiler chicks (n=5) were sampled at day after hatch and
days 3, 5, 7, 10, 12, 14, 17, and 21 posthatch, and mRNA expression level was measured
using absolute quantitation. The small intestine (duodenum, jejunum, and ileum) expressed
the largest quantities of each gene tested. The expression in the ceca and liver was
1 to 3 orders of magnitude less than that of the small intestine. The expression of
basolateral transporters in the small intestine was more constant over days posthatch
than the expression of brush border transporters. In the ceca the expression of the
brush border transporters decreased over the sampling period, while expression of
basolateral genes was relatively constant. In the liver the expression of Na+ independent
cationic and zwitterionic amino acid transporter (bo,+AT), Na+ independent cationic
amino acid transporter 2 (CAT2), excitatory amino acid transporter 3 (EAAT3), and
the heavy chain corresponding to the bo,+) system (rBAT) significantly decreased at
12 days posthatch; however, the expression of Na+ independent cationic and Na+ dependent
neutral amino acid transporter 1 (y+LAT1), Na+ coupled neutral amino acid transporter
1; (SNAT1), and Na+ coupled neutral amino acid transporter 2 (SNAT2) significantly
increased at day 5 posthatch compared to day 1 and these levels remained throughout
the rest of the sampling period. The current results suggest that at 1 day posthatch
chicks are capable of AA processing and transport in the intestine as well as the
liver. Additionally the ability of the ceca in transporting AA from the lumen may
decrease with age. The liver should be capable of amino acid transport, but its capabilities
may be more specific since the expression of several transporters in this organ is
either absent or very low.