Objective The study was carried out to investigate the effects of different dietary Ca levels on bone metabolism, based on the osteoprotegerin ( OPG)-receptor activator of NF?κB ligand ( RANKL)?receptor activator of NF?κB ( RANK) system in growing WHBE rabbits. Methods Twenty one weaned male WHBE rabbits at the age of 42 days were divided into 3 groups (I, II and III) according to dietary Ca levels (0. 95%, 1. 10%, and 1. 30%, respectively) for a 42?d feeding trial. The above three diets had similar phosphor (P) (about 0. 64 g/kg), digestible energy (9. 50 MJ/kg), crude protein (about 19. 70%) and crude fibre (13. 57%) contents. When the feeding trial finished, the serum in?dices of bone metabolism (Ca, PTH and BALP) were detected, and the OPG?RANK?RANKL system in bone tissue was analyzed by real?time fluorescence quantitative PCR assay and immunohistochemistry, respectively. At last, the relationships between bone metabolism and dietary Ca were evaluated according to RANKL/OPG ratio. Results All the contents of serum Ca, PTH and BALP had no significant differences in the groups I, II and III (P>0. 05). Both the RANKL mR?NA and RANKL/OPG mRNA ratio were lowest in the group II and had significant differences with group I and III ( P<0. 05). Dietary Ca levels had significant effects on the protein expression of OPG?RANK?RANKL in bone tissues (P<0. 01). The positive index of OPG in the groups II and III was significantly higher than that in the group I(P<0. 01), while the positive index of RANK in the group II was lower than those of the group I and III(P<0. 01). The protein ex?pression positive index ratio of RANKL to OPG was also lowest in the group II, showing a significant difference with group I(P<0. 01). Furthermore, both the gene transcription ratio of RANKL to OPG and the protein expression positive index ratio of RANKL to OPG had significant correlations (with quadratic curve) to the dietary Ca levels (R2 =0. 4068, 0. 8433;P<0. 05,P<0. 001). Conclusions In summary, the bone metabolism of WHBE rabbits during growing periods has sig?nificant correlation with dietary Ca levels. An optimal bone metabolism status can be obtain at 1. 10% dietary Ca level as demonstrated in this study.%目的 利用护骨素-核因子κB受体活化子?核因子κB受体活化子配体(OPG?RANK?RANKL)系统,探讨饲粮不同钙水平对生长期WHBE兔骨代谢影响.方法 选择21只雄性断奶WHBE兔,随机分为3组(I、II、III组),分别饲以钙水平为0.95%,1.10%和1.30%,其他营养水平基本一致的饲粮.实验期42 d.实验结束,测定兔血清钙(Ca)、甲状旁腺素(PTH)和骨源性碱性酶(BALP)含量;分别运用荧光定量PCR法和免疫组织化学法对WHBE兔骨组织进行OPG?RANK?RANKL的基因转录和蛋白表达分析.最后以RANKL/OPG比值为指标,评估WHBE兔骨代谢与饲粮钙水平间的相关性.结果 实验结果表明,I、II、III组在血清Ca、PTH含量和BALP活力上差异无显著性(P>0.05).WHBE兔骨组织RANKL mRNA表达水平和RANKL/OPG mRNA比值均以II组最低,与I、III组差异有显著性(P<0.05).钙水平对WHBE兔骨组织OPG?RANK?RANKL蛋白表达影响显著(P<0.01),II组和III组OPG蛋白表达阳性指数均极显著高于I组(P<0.01);而II组兔骨组织RANK蛋白表达阳性指数则极显著低于I组和III组(P<0.01),RANKL/OPG的蛋白表达阳性指数比值以II组最低,与I组差异有显著性(P<0.01).此外,WHBE兔骨组织RANKL/OPG mRNA比值和的蛋白表达阳性指数比值均与饲粮钙水平间存在显著的二次曲线相关(R2=0.4068,0.8433,P<0.05,P<0.001).结论 生长期WHBE兔的骨代谢与饲粮钙水平间呈显著相关性,当饲粮钙含量为1.10%时,生长期WHBE兔可获得较理想的骨代谢水平.
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