In poultry, obesity is partly influenced by food intake, and is increasingly becoming a nationwide problem. Hypothalamic food intake mechanisms are involved metabolically and neurologically via two peptide hormones, leptin and ghrelin, and the amino acid glutamate, which is enzymatically derived from lysine metabolism. We hypothesize that lysine homeostasis mediates regulation of feed intake and performance characteristics via the brain-liver axis through glutamate sensing. The objective was to examine the effects of lysine homeostasis in avian food regulation and performance through neuroendocrine signaling. One-day-old male French Guinea fowl (GF) keets (n = 270) were weighed and randomly assigned to 5 dietary treatments (0.80%, 0.86%, 0.92%, 1.10% control, and 1.22% lysine) in 3 replicates. At 4 and 8 wk of age 20% of experimental birds were randomly selected, weighed and euthanatized. The liver, pancreas, and hypothalamus were excised, snap frozen in liquid nitrogen and stored at -80°C until use. Tissue mRNA was extracted and cDNA synthesized for qPCR assays. Lysine at 0.80 and 0.86% hindered growth, development of digestive organs, expression of brain and liver glutamate and leptin receptors, and caused high mortality in GF. The fold change for metabotropic glutamate receptor I was lower (P < 0.05) in liver and higher in brain at 0.86 and 0.92% than the control (1.10%) and 1.22% lysine. The 1.22% lysine exhibited highest expression of ionotropic glutamate receptor, while brain ghrelin receptor expression was highest at 0.86 and 0.92% lysine. Therefore, dietary lysine concentration may influence signaling pathways regulating food intake in brain-liver axis via glutamate synthesis.
The identities of genes that underlie population variation in adipose tissue development in farm animals are poorly understood. Previous studies in our laboratory have suggested that increased fat tissue involves the expression modulation of an array of genes in broiler chickens. Of special interest are eight genes, FGFR3, EPHB2, IGFBP2, GREM1, TNC, COL3A1, ACBD7, and SCD. To understand their expression regulation and response to dietary manipulation, we investigated their mRNA levels after dietary manipulation during early development. Chickens were fed either a recommended standard or a high caloric diet from hatch to eight weeks of age (WOA). The high caloric diet markedly affected bodyweight of the broiler birds. mRNA levels of the eight genes in the abdominal adipose tissue were assayed at 2, 4, 6, and 8 WOA using RT-qPCR. Results indicate that (1) FGFR3 mRNA level was affected significantly by diet, age, and diet:age interaction; (2) COL3A mRNA level was repressed by high caloric diet; (3) mRNA levels of EPHB2, ACBD7, and SCD were affected by age; (4) mRNA level of TNC was modulated by age:diet interaction; (5) changes in GREM1 and IGFBP2 mRNA levels were not statistically different.
Twenty-four, 4-week-old rabbits were fed diets placed on the same ration did not exhibit de-
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