NUTRITIONAL REGUILATION OF INSULIN-LIKE GROWTH FACTOR BINDING PROTEIN-2 GENE EXPRESSION IN THE CHICKEN

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The influence of feeding with experimental diets containing different dietary protein quantity and quality on changes in IGFBP-2 gene expression in various tissues of young chickens was examined. The hepatic IGFBP-2 mRNA was not detected among all treatments. When chickens fed a 5% soybean diet, brain IGFBP-2 mRNA level was lower than that of chickens fed a 20% soybean diets supplemented with essential amino acids. In the gizzard, IGFBP-2 mRNA in the group of a 20% soybean diets supplemented with essential amino acids was significantly lower than other groups. There was no significant difference in IGFBP-2 gene expression in the kidney among all treatments. These results suggest that the difference in dietary protein quantity affect IGFBP-2 gene expression in brain and gizzard, and that the difference in dietary protein quality affects IGFBP-2 gene expression in only gizzard. The expression of IGFBP-2 gene might be less responsive to the difference in dietary protein quality than that in dietary protein quantity.The changes in tissue IGFBP-2 gene expression of young fasted chickens followed by refeeding a commercial diet or by administrating bovine insulin was examined. Hepatic IGFBP-2 mRNA was significantly increased by fasting for 2 days and decreased by refeeding for 6 h. Insulin administration also decreased hepatic IGFBP-2 gene expression stimulated by fasting to the level of refed chickens. IGFBP-2 mRNA in the gizzard was significantly increased by fasting for 2 days and tended to decrease by refeeding for 6 h. Insulin administration decreased gizzard IGFBP-2 gene expression lower than the level of refed chickens. There was no significant difference in IGFBP-2 mRNA in the brain and kidney among all treatments. These results suggest that the changes in IGFBP-2 gene expression in the liver and gizzard by fasting and refeeding might be partly regulated by the alteration in plasma insulin concentration.