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Poultry and Laboratory Animal Nutrition
Asian-Australasian Journal of Animal Sciences 2011;24(2): 239-245.
https://doi.org/10.5713/ajas.2011.10059    Published online December 21, 2010.
Effect of Excessive Vitamin A on Alkaline Phosphatase Activity and Concentrations of Calcium-binding Protein and Bone Gla-protein in Culture Medium and CaBP mRNA Expression in Osteoblasts of Broiler Chickens
Xiaoyu Guo, Sumei Yan, Binlin Shi, Yongmiao Feng
This study was conducted to determine the effects of excess vitamin A on alkaline phosphatase (ALP) activity, contents of calcium-binding protein (CaBP), bone gla-protein (BGP) in culture medium and CaBP mRNA expression in chicken osteoblasts in vitro. Osteoblastic cells in the tibia from 1-day-old Arbor Acre broiler chickens were isolated using enzyme digestion. The subconfluenced cells were divided into eight treatments with six replicates in each treatment and cultured in a medium containing either vehicle or different levels of vitamin A (0, 0.2, 0.6, 1.0, 2.0, 5.0, 10.0 and 20.0 g/ml), and the control received an equivalent volume of ethanol. The incubation lasted 48 h. The results showed that vitamin A down-regulated ALP activity in the culture medium as well as CaBP mRNA expression of osteoblasts in a linear dose-dependent manner (p = 0.124 and p<0.10, respectively), and suppressed the contents of BGP and CaBP in the culture medium in a quadratic dose-dependent manner (p<0.05 and p<0.10, respectively) with increasing addition of vitamin A. The addition of 0-0.2 g/ml vitamin A to the culture medium increased ALP activity, BGP and CaBP contents as well as CaBP mRNA expression compared with other groups, but positive effects of vitamin A tended to be suppressed when vitamin A was increased to 1.0 g/ml, and adverse effects occurred when vitamin A was increased to 10.0-20.0 g/ml. These results implied that there was a threshold level of vitamin A inclusion beyond which inhibitory effects occurred, and the mechanism by which overdose of vitamin A reduced bone growth in chickens was probably reduced osteoblastic cell activity, and inhibited expression of CaBP mRNA and CaBP secretion.
Keywords: Vitamin A; Broiler Chicken; Calcium-binding Protein; mRNA Expression; Osteoblast; Bone Gla-protein
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