Protein Restriction with Amino Acid-Balanced Diets Shrinks Circulating Pool Size of Amino Acid by Decreasing Expression of Specific Transporters in the Small Intestine.
Dietary protein restriction is not only beneficial to health and longevity in humans, but also protects against air pollution and minimizes feeding cost in livestock production. However, its impact on amino acid (AA) absorption and metabolism is not quite understood. Therefore, the study aimed to explore the effect of protein restriction on nitrogen balance, circulating AA pool size, and AA absorption using a pig model. In Exp.1, 72 gilts weighting 29.9 ± 1.5 kg were allocated to 1 of the 3 diets containing 14, 16, or 18% CP for a 28-d trial. Growth (n = 24), nitrogen balance (n = 6), and the expression of small intestinal AA and peptide transporters (n = 6) were evaluated. In Exp.2, 12 barrows weighting 22.7 ± 1.3 kg were surgically fitted with catheters in the portal and jejunal veins as well as the carotid artery and assigned to a diet containing 14 or 18% CP. A series of blood samples were collected before and after feeding for determining the pool size of circulating AA and AA absorption in the portal vein, respectively. Protein restriction did not sacrifice body weight gain and protein retention, since nitrogen digestibility was increased as dietary protein content reduced. However, the pool size of circulating AA except for lysine and threonine, and most AA flux through the portal vein were reduced in pigs fed the low protein diet. Meanwhile, the expression of peptide transporter 1 (PepT-1) was stimulated, but the expression of the neutral and cationic AA transporter systems was depressed. These results evidenced that protein restriction with essential AA-balanced diets, decreased AA absorption and reduced circulating AA pool size. Increased expression of small intestinal peptide transporter PepT-1 could not compensate for the depressed expression of jejunal AA transporters for AA absorption.
State Key Lab of Animal Nutrition & Ministry of Agriculture Feed Industry Centre, College of Animal Science & Technology, China Agricultural University, Beijing, 100193, China.
Kai
K
Qiu
State Key Lab of Animal Nutrition & Ministry of Agriculture Feed Industry Centre, College of Animal Science & Technology, China Agricultural University, Beijing, 100193, China.
Chun Fu
CF
Qin
Chongqing Academy of Animal Science, Rongchang, Chongqing, 450023, China.
Min
M
Luo
State Key Lab of Animal Nutrition & Ministry of Agriculture Feed Industry Centre, College of Animal Science & Technology, China Agricultural University, Beijing, 100193, China.
Xin
X
Zhang
State Key Lab of Animal Nutrition & Ministry of Agriculture Feed Industry Centre, College of Animal Science & Technology, China Agricultural University, Beijing, 100193, China.
Wen Juan
WJ
Sun
State Key Lab of Animal Nutrition & Ministry of Agriculture Feed Industry Centre, College of Animal Science & Technology, China Agricultural University, Beijing, 100193, China.
Ning
N
Jiao
State Key Lab of Animal Nutrition & Ministry of Agriculture Feed Industry Centre, College of Animal Science & Technology, China Agricultural University, Beijing, 100193, China.
De Fa
de F
Li
State Key Lab of Animal Nutrition & Ministry of Agriculture Feed Industry Centre, College of Animal Science & Technology, China Agricultural University, Beijing, 100193, China.
Jing Dong
JD
Yin
D000596:Amino Acids / Q000494:pharmacology*; D000821:Animal Feed; D000818:Animals; D015153:Blotting, Western; D001835:Body Weight / Q000187:drug effects; D004435:Eating / Q000187:drug effects; D007421:Intestine, Small / Q000187:drug effects / Q000378:metabolism*; D007583:Jejunum / Q000187:drug effects / Q000378:metabolism; D008962:Models, Theoretical; D009584:Nitrogen / Q000378:metabolism; D013552:Swine
D000596:Amino Acids; D009584:Nitrogen