Abstract:

【Objective】 A study was conducted to determine the role of vitamin D3 in regulating phosphate (Pi) intake. 【Method】 A total of 40 male Kunming-rats aged at 21days was randomly divided into 2 treatments, each treatment consisted of 5 replicates with 4 rats. The two treatments were fed with the basal diet supplemented with 0.2 % (low-Pi) or 0.6 % (normal-Pi) phosphate (total phosphate). The experiment lasted for 7 days. On the former 6 days, each of the replicates was treated with EHDP (ethane-1-hydroxy-1,1-diphosphonicacid,tetrasodiumsalt) which is known to decrease the circulating levels of 1,25-(OH)2D3. Before twelve hours before slaughter, two of the replicates were injected with 1,25-(OH)2D3 at 600ng/kg.wt, and used as treatment group, the no 1,25-(OH)2D3 injection group was used as control. On the 7th day morning, rats were slaughtered for determination of Ca (calcium) and Pi (phosphate) concentration and phosphate uptake. 【Result】 Results showed that phosphate levels significantly affected the Ca and Pi concentration of bone; That of low- Pi treated group was 3.33 folds (P＜0.01) and 3.03 folds (P＜0.01) than normal Pi treatment under VD3 stress; VD3 concentration of the two treatment groups was 3.08 (P＜0.01) folds and 2.32 folds(P＜0.01)higher than the control group. NaPi-IIb mRNA expression of 0.2 % Pi treatment group was significantly higher than the control group. NaPi-IIb mRNA expression in ileum and duodenum of 0.2% Pi treatment group was 14.53 folds higher and 9.80 higher folds than 0.6% Pi treatment group, and the difference was significant (P＜0.01). Pi uptake of treatment groups of two phosphate levels was significantly (P＜0.01 or P＜0.05) higher than the control group, respectively by51.76%, 62.68%, 57.79%, and 47.37% of in ileum, jejunum and duodenum and renal in 0.2% Pi treatment group, while 18.19%, 39.22%, 54.72%, and 39.83% in 0.6 % Pi treatment group.【Conclusion】The results showed that vitamin D3 plays an important role in regulation Pi uptake under low phosphate. Injection of 1,25-(OH)2D3 increased the expression of NaPi-IIb mRNA and Pi uptake of rats; The effects of VD3 on improvement of Pi uptake decreased with increasing dietary phosphate level.

Key words: NaPi-Ⅱb, low phosphate, uptake, vitaminD3, rat