Article Cite This: J. Agric. Food Chem. 2019, 67, 6809−6818
pubs.acs.org/JAFC
Dietary Branched-Chain Amino Acids Regulate Food Intake Partly through Intestinal and Hypothalamic Amino Acid Receptors in Piglets Min Tian,† Jinghui Heng,† Hanqing Song,† Kui Shi,† Xiaofeng Lin,† Fang Chen,† Wutai Guan,*,†,‡ and Shihai Zhang*,†,‡
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Guangdong Province Key Laboratory of Animal Nutrition Control, College of Animal Science, South China Agricultural University, Guangzhou, 510642, China ‡ College of Animal Science and National Engineering Research Center for Breeding Swine Industry, South China Agricultural University, Guangzhou 510642, China ABSTRACT: Strategies to increase feed intake are of great importance for producing more meat in swine production. Intestinal and hypothalamic amino acid receptors are found to largely participate in feed intake regulation. The purpose of the current research is to study the function of branched-chain amino acid (BCAA) supplementation in the regulation of feed intake through sensors that can detect amino acids in piglets. Twenty-four piglets were assigned one of four treatments and fed one of the experimental diets for either a short period (Expt. 1) or a long period (Expt. 2): a normal protein diet (NP, 20.04% CP), a reduced-protein diet (RP, 17.05% CP), or a reduced-protein test diet supplemented with one of two doses of BCAAs (BCAA1, supplemented with 0.13% L-isoleucine, 0.09% L-leucine, and 0.23% L-valine; BCAA2, supplemented with the 150% standardized ileal digestibility BCAA requirement, as recommended by the National Research Council (2012)). In Expt. 1, no differences were observed in the feed intake among piglets fed different diets (P > 0.05). In Expt. 2, compared with the RP group, the feed intake of piglets was significantly increased after sufficient BCAAs were supplemented in the BCAA1 group, which was associated with decreased cholecystokinin secretion (P < 0.05), down-regulated expression of type-1 taste receptors 1/3 (T1R1/T1R3) in the intestine, as well as increased expression of pro-opiomelanocortin, activated general control nonderepressible 2 (GCN2), and eukaryotic initiation factor 2α (eIF2α) in the hypothalamus (P < 0.05). However, the feed intake was decreased for unknown reasons when the piglets were fed a BCAA over-supplemented diet. Our study confirmed that a BCAA-deficient diet inhibited feed intake through two potential ways: regulating the amino acid T1R1/T1R3 receptor in the intestine or activating GCN2/eIF2α pathways in the hypothalamus. KEYWORDS: amino acid receptor, branched-chain amino acids, feed intake, reduced-protein diet
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INTRODUCTION
BCAAs and feed intake, the underlying mechanism is still largely unknown. Animals detect and sense diverse dietary nutrients via intestinal enteroendocrine cells (EECs) before they are absorbed into the blood. EECs are distributed along the gastrointestinal (GI) tract, but they are 0.10) among piglets fed different diets. In Expt. 2, the growth performance of piglets is listed in Table 4. During the first week, no differences (P > 0.10) were observed in the growth performances among NP, RP, BCAA1, and BCAA2 groups. Compared with the NP group, ADG and ADFI in the RP group were significantly decreased (P < 0.05) in the second and third weeks. Interestingly, the BCAA1 group showed an increase (P < 0.05) in ADG and ADFI
Table 4. Long-Term Feeding Experiment in Piglets Fed a Low-Protein Diet Deficient in BCAAs (Expt. 2)a treatments items initial BW (kg) final BW (kg) ADFI (g/day) week 1 week 2 week 3 overall ADG (g/day) week 1 week 2 week 3 overall G/F week 1 week 2 week 3 overall
NP
RP
BCAA1
BCAA2
SEM
P
10.48 21.96a
10.39 18.59b
10.40 21.03a
10.51 20.14ab
0.41 0.79
1.00 0.04
582 825a 925a 777
565 678b 756b 666
578 774ab 912a 754
575 696b 819b 523
61 40 35 123
1.00 0.04 0.01 0.59
397 552a 639a 529
347 411c 436c 398
367 500ab 584ab 484
359 460bc 525b 448
35 22 23 52
0.78 0.01
