Effects of dietary protein and amino acid levels on the expression of selected cationic amino acid transporters and serum amino acid concentration in growing pigs

Abstract

The absorption of lysine is facilitated by leucine, but there is no information regarding the effect of crude protein, lysine and leucine levels on the expression of cationic amino acid transporters in pigs. Therefore, an experiment was conducted with 20 pigs (14.9 +/- 0.62 kg initial body weight) to evaluate the effect of two protein levels, and the content of lysine, threonine, methionine and leucine in low crude protein diets on the expression of b(0,+) and CAT-1 mRNA in jejunum, Longissimus dorsi and Semitendinosus muscles and serum concentration of amino acids. Treatments were as follows: (i) wheat-soybean meal diet, 20% crude protein (Control); (ii) wheat diet deficient in lysine, threonine and methionine (Basal diet); (iii) Basal diet plus 0.70% L-lysine, 0.27% L-threonine, 0.10% DL-methionine (Diet LTM); (iv) Diet LTM plus 0.80% L-leucine (Diet LTM + Leu). Despite the Basal diet, all diets were formulated to meet the requirements of lysine, threonine and methionine; Diet LTM + Leu supplied 60% excess of leucine. The addition of lysine, threonine and methionine in Diet LTM increased the expression of b(0,+) in jejunum and CAT-1 in the Semitendinosus and Longissiums muscles and decreased CAT-1 in jejunum; the serum concentration of lysine was also increased (p < 0.01). Further addition of L-leucine (Diet LTM + Leu) decreased the b(0,+) expression in jejunum and CAT-1 in the Longissimus dorsi muscle (p < 0.05), increased the serum concentration ofleucine and arginine and decreased the concentration of isoleucine (p < 0.05). Pigs fed the Control diet expressed less b(0,+) in jejunum, and CAT-1 in the Semitendinosus and Longissiums muscles expressed more CAT-1 in jejunum (p < 0.05) and had lower serum concentration ofisoleucine, leucine and valine (p < 0.05), but higher lysine concentrations (p < 0.01) than those fed Diet LTM. These results indicated that both, the level and the source of dietary amino acids, affect the expression of cationic amino acid transporters in pigs fed wheat-based diets.

Expression of genes coding for selected amino acid transporters in small intestine, liver, and skeletal muscle of pigs fed excess branched-chain amino acids

“…Variations in CAT1 expression in the skeletal muscle of pigs due to different dietary AA levels have been reported. García-Villalobos et al (2012) found that adequate, as compared to deficient levels of Lys, Thr, and Met, increased the expression of CAT1 in LD. In contrast, we found that excess Leu or excess LIV did not affect CAT1 expression in the LD.…”

“…The transporter b 0 , + AT exchanges Lys for neutral AA, particularly Leu Majumder et al, 2009) AT that is coupled with the efflux of Leu (Pineda et al, 2004). We recently observed reduced expression of b 0 , + AT in growing pigs (García-Villalobos et al, 2012;Morales et al, 2013) fed excess Leu diets, and surplus Ile failed to correct the reduction (Cervantes-Ramírez et al, 2013). However, there is limited information regarding the effect of adding surplus Ile and Val to diets with excess Leu on the abundance of transport systems for BCAA and cationic AA (Lys) in growing pigs.…”

Gene expression, serum amino acid levels, and growth performance of pigs fed dietary leucine and lysine at different ratios

“…The b 0,+ system, which exchanges Leu for Lys (Torras-Llort et al, 2001), is the most important Lys transporter in the small intestine, and the absorption of Lys by b 0,+ is coupled with Leu efflux (Pineda et al, 2004). However, excess levels of dietary Leu appear to reduce Lys availability by decreasing the expression of b 0,+ (García-Villalobos et al, 2012). Leu stimulates muscle protein synthesis in pigs, and this stimulation is dependent on amino acid availability, but excess Leu may affect Lys absorption.…”

Expression of cationic amino acid transporters, carcass traits, and performance of growing pigs fed low-protein amino acid-supplemented versus high protein diets

“…Morales et al (2012) also found a significant increase in the expression of b 0,+ in jejunum of growing pigs fed low CP, as compared to PB-AA (11.0 vs 19.0%) wheat-based diets. Yue and Qiao (2008) observed that reducing dietary CP concentration from 23.1 to 17.2% decreased the villous height in duodenum and jejunum; this suggests a decrease in the number of small intestine absorptive cells.…”

“…The b 0,+ system exchanges Leu for Lys (Torras-Llort et al, 2001), indicating that the intestinal absorption of Lys is coupled with the efflux of Leu. A recent report shows that the dietary content of Leu and Lys affects the absorption of Lys (García-Villalobos et al, 2012). F-AA diets not only contain lower Arg and Leu levels but also a high percentage of free Lys, from 44% (Kerr et al, 2003) to 70% (Barrera et al, 2004) of total Lys.…”