Effects Of Zinc On Bone Metabolism And Related Genes Expression Of SD Rats

Zinc (Zn) is an essential trace element for animals. It has been demonstrated thatzinc is involved in many physiological reactions, including growth, development,reproduction and immune system. Zinc also plays an important role in bonemetabolism. The effect of zinc on bone metabolism and related functional genesexpression in SD rats was conducted in this study, which was helpful to offer atheoretical foundation for elucidating the mechanism of action of zinc in the processof bone formation.Four diets, including Zn adequate (ZA; 46.39 mg/kg, control), Zn deficient (ZD;3.20 mg/kg), Zn overdose (ZO; 234.39 mg/kg), and pair-fed (PF, which received thezinc-adequate diet in an equivalent amount consumed by zinc-deficient partner duringthe previous 24-h period), were fed to rats for 5 weeks. The basic diet consumed byall animals in this study was formulated according to AIN-93G purified diet. Onehundred male Sprague-Dawley outbred weaning rats (d-21 old and weighing 95±5g)were used in this study. The rats were randomly divided into four equal groups (n=25).The animals were housed in stainless steel hanging cages under a barrier system andin each group were equally divided and kept in five cages (5 rats/cage). All rats wereweighted upon arrival and weekly thereafter. The results were listed as follows:Zinc levels affected growth and development of bone. Compared with ZA group, thefemur to body weight ratio of ZD, ZO and PF was all decreased by 18.9% (P＜0.01),but there were no differences (P＞0.05) between ZD and PF groups. Zinc alsosignificantly influenced bone metabolism. Compared with ZA group, theconcentrations of femur Ca, P and Zn were markedly declined by 19.0 % (P＜0.01),21.9% (P＜0.01) and 39.2 % (P＜0.01) in ZD group, respectively, but those in ZOgroup showed no difference (P＞0.05). Femur Zn concentration in PF group had17.3% (P＜0.01) lower than that of ZA group. Serum alkaline phosphatase (ALP)activity, and Zn, Ca, and P contents were also measured. The results showed that ALPactivity and Ca contents in ZD group were descended by 30.9% (P＜0.01) and 18.2%(P＜0.05), respectively, but Zn and P contents were unaffected (P＞0.05), compared with ZA. There were no changes (P＞0.05) in serum ALP, Zn, Ca and P in both ZO andPF groups as compared with ZA group. In addition, compared with ZA group, hepaticZn levels showed no difference (P＞0.05) in both ZD and PF groups, but wereincreased 19.8% (P＜0.05) in ZO group.Compared with ZA group, the metabolic rates of Ca, P and Zn were markedlyreduced by 23.6% (P＜0.01), 20.5% (P＜0.01) and 31.9% (P＜0.01) in ZD rats,respectively, but no difference (P＞0.05) in ZO rats. However, those measurementswere increased by 29.4% (P＜0.01), 21.4% (P＜0.01) and 18.8% (P＜0.01) in PF group,respectively, as compared with ZA group.The comparison between ZD and PF groups were specially conducted in presentstudy. The results showed that femur Ca, P and Zn contents in ZD group weredecreased by 26.4 (P＜0.01), 19.8 (P＜0.01) and 20.3% (P＜0.01), respectively; serumALP activity and Ca content in ZD group were 23.2% (P＜0.01) and 23.2% (P＜0.05)lower than that of PF group; there were no differences (P＞0.05) in hepatic Zn contentbetween ZD and PF groups. The metabolic rate of Ca, P and Zn was reduced by41.0% (P＜0.01 ), 34.5% (P＜0.01 ) and 42.7% (P＜0.01) in ZD group, respectively.The effect of zinc on mRNA levels of some key genes involved in bone metabolism,such as alkaline phosphatase (ALP), carbonic anhydrases (CA), growth hormonereceptor (GHR) and insulin-like growth factor-Ⅰ(IGF-Ⅰ) was studied. Compare withZA group, ALP mRNA levels of ZD and PF group was declined by 41.4% (P＜0.01)and 30.3% (P＜0.01), respectively, there were no differences (P＞0.05) between ZO andZA group; GHR mRNA levels of ZD and PF rats had 23.5% (P＜0.05) and 33.9%(P＜0.05) higher than that of ZA rats, respectively, and no difference was observed inZO rats versus ZA rats; IGF-ⅠmRNA level in ZD group was reduced by 26.7 (P＜0.05),and unchanged (P＞0.05) in both ZO and PF group compared with ZA group. However,CA mRNA levels were not affected (P＞0.05) by different zinc levels. Zn deficiencyhad no effect on mRNA levels of genes mentioned above except IGF-ⅠmRNA levelswere which were decreased by 28.9% (P＜0.05) as compared with PF group.