Effect of hyperphosphatemia on gene expression of the Na-Pi cotransporter in rats.

We investigated the effect of high phosphorus content on the sodium-phosphate cotransporter (NaPi-IIa and NaPi-IIl). Forty-eight Sprague-Dawley rats were divided into 3 groups: high-phosphorus group (HP) with fructose diphosphate sodium injection; self-manufactured low-phosphorus diet group (LP); and normal diet group (NP). At the 1st, 2nd, 4th, and 6th weeks, 4 rats from each group were sacrificed for detecting serum levels of calcium, phosphorus, and intact parathyroid hormone. Semi-quantitative retrovirus-polymerase chain reaction was used to detect the expression of NaPi-IIa and NaPi-III mRNA in kidney. At the 1st, 2nd, 4th, and 6th weeks, serum phosphorus and parathyroid hormone levels in HP group were significantly higher than those in LP and NP groups (P < 0.05). Serum calcium levels in the 3 groups showed no difference (P > 0.05). Comparing the expression of NaPi-IIa mRNA in HP group with LP and NP groups, NaPi-IIa mRNA expression was significantly reduced in HP group (P < 0.05), while NaPi-IIa mRNA expression in LP group began increasing at the 4th week (P < 0.05). At the 1st, 2nd, and 4th weeks, the expression of NaPi-III mRNA in HP, LP, and NP groups showed no clear differences (P > 0.05), while at the 6th week in HP group, NaPi-III mRNA expression was slightly increased compared to in LP and NP groups (P < 0.05). Hyperphosphatemia significantly affected NaPi-IIa and NaPi-III mRNA expression, and a factor promote an increase in intact parathyroid hormone independently of calcium.

Establishment and characterization of a rat model of hyperphosphatemia.

We established a rat model of hyperphosphatemia and investigated the systemic effects of high phosphorus (P). Sprague Dawley rats were randomly divided into high (HP), low (LP), and normal (NP) P groups (N = 12 each), which received injections of fructose diphosphate sodium, or were fed self-manufactured low phosphorus or normal diets, respectively. In each group, 4 rats were sacrificed at the first, third, and sixth week to detect the serum (Scr) and urinary creatinine and P, and calcium (Ca) levels. The HP group's serum P and intact parathyroid hormone (iPTH) were significantly higher than those in the other groups at the first, third, and sixth weeks, (P < 0.05); the LP group's serum P was lower than the NP group's at the third week (P < 0.05), while at the sixth week, the serum P and iPTH were lower (P < 0.05). No significant differences were detected for blood Ca+ (P > 0.05). The HP group's Scr increased (P < 0.01), whereas the fractional excretion decreased (P < 0.05) significantly. Thighbone and lumbar spine bone densities differed significantly between groups in the third week (P < 0.05); LP group densities were lower than NP group measures (P < 0.05). Crystallized stones were not observed microscopically following hematoxylin and eosin staining of the kidney. We successfully established a hyperphosphatemia rat model, and high blood P was found to significantly influence renal function and bone density. These results might provide a foundation to study the effects of hyperphosphatemia in rats.