Differential effects of L-alanine, L-glutamine, L-arginine HCl, and glycine on feed intake and hypothalamic appetite-related responses in layer-type chicks

Introduction While the effects of L-alanine, L-glutamine, L-arginine monohydrochloride (L-arginine HCl) and glycine on feed intake (FI) have been studied in chicks, their hypothalamic neuropeptide responses in layers remain unclear. Methods Therefore, four trials were conducted to investigate the central effects of these amino acids on feed intake and hypothalamic neuropeptides in layer chicks. After intracerebroventricular administration, cumulative FI was measured over 2 hours and gene expression levels were determined using RT-PCR. Results Our results showed that L-alanine (1 µg and 2 µg) decreased FI at 120 minutes post-injection and was associated with decreased neuropeptide Y (NPY) mRNA expression ( P < 0.05). L-glutamine (3 µg) increased FI at 60 minutes post-injection ( P < 0.05), but had no significant effect on proopiomelanocortin (POMC), NPY, melanocortin receptor 4 (MC4R) or agouti-related peptide (AgRP) ( P > 0.05). L-arginine HCl (1 µg) decreased FI at 120 minutes post-injection, while increasing POMC and MC4R expression, and decreasing NPY ( P < 0.05). Glycine (3 µg) significantly reduced FI at all measured time intervals ( P < 0.05). It had no impact on POMC expression ( P > 0.05), but increased MC4R expression ( P < 0.05) and reduced NPY expression more than AgRP expression, although neither was significantly decreased ( P > 0.05). Conclusion These results suggest that the effect of individual amino acids on FI and hypothalamic neuropeptide expression in layer chicks depends on the type and dose of amino acid. The present findings provide evidence of the acute central effects of amino acids in layer chicks.