Insulin-Like Growth Factor Binding Protein-2 Gene Expression Can Be Regulated by Diet Manipulation in Several Tissues of Young Chickens

The relationship between nutritional status and insulin-like growth factor binding protein-2 (IGFBP-2) gene expression in chickens was studied. Chickens (6 wk old) were food deprived for 2 d and then refed. IGFBP-2 mRNA in the brain was significantly decreased by food deprivation and levels did not increase when birds were refed for 24 h. Gizzard and hepatic IGFBP-2 mRNA levels were significantly increased by food deprivation and decreased by refeeding. Any nutrients tested decreased hepatic IGFBP-2 gene expression. In kidney, IGFBP-2 mRNA was detected but not influenced by food deprivation and refeeding. In another study, the influence of dietary protein source [isolated soybean protein vs. casein; crude protein (CP) 20%] and the supplementation of essential amino acids on IGFBP-2 gene expression of young chickens (5 wk old) was examined. The influence of feeding a low soybean protein diet (CP 5%) on tissue IGFBP-2 gene expression was also investigated. Hepatic IGFBP-2 mRNA was not detected in any group. Feeding the low protein diet for 7 d decreased brain IGFBP-2 mRNA level and increased gizzard IGFBP-2 level compared with chickens fed 20% protein diets. A significant interaction between protein source and amino acid supplementation was observed in gizzard IGFBP-2 mRNA level. In both casein-fed groups and in chickens fed 20% soybean protein diet without supplemental amino acids, the levels did not differ from one another or from the low protein diet–fed birds. The level was lower in chickens fed the amino acid–supplemented, 20% soybean protein diet. In conclusion, the response of IGFBP-2 gene expression to variations in nutritional status was rapid and different in several tissues of young chickens, which would help modulate the growth-promoting effect of circulating IGF-I by making the IGF-IGFBP complex.