“…Lysine and arginine are transported in the intestinal basolateral layer by the CAT1 transporter, whose gene expression is regulated by factors, including nutrient type and density, hormones and growth factors (He et al., 2013 ; Pineda et al., 2004 ; Wang et al., 2017 ). Intestinal amino acid and peptide transporters are regulated by various factors, including genetic improvement, age, intestinal development, medicinal agents, form of feed, pathological states and nutrient density (Chen et al., 2005 ; Gilbert et al., 2008 ; He et al., 2013 ; Mahdavi et al., 2018 ; Morales et al., 2017 ; Osmanyan et al., 2018 ). Earlier studies suggest that the mRNA abundance of intestinal amino acid and peptide transporters in animals is regulated through various mechanisms, such as adaptive regulation theory (Hatzoglou et al., 2004 ), amino acid sensory pathways and amino acid‐responsive element (Fafournoux et al., 2000 ), peroxisome proliferator‐activated receptor‐α (PPARα; Shimakura et al., 2006 ), substrate supply to the intestine and intra‐enterocyte space (the 5´ upstream region of PepT1 contains substrate‐responsive elements; Chen et al., 2005 ; Mahdavi et al., 2018 ), increased mRNA stability and transcription rate (Adibi, 2003 ), plasma thyroxin (T4) levels and the state of intestinal villi (Mahdavi et al., 2018 ).…”