Reduced bone mineral density and increased urinary phosphate excretionin zinc-deficient rats

Abstract

This study assessed bone mineral density (BMD) using dual-energy x-ray absorptiometry (DXA), the alkaline phosphatase (ALP) and tartrate-resistant acid phosphatase (TRAP) activity in the femur, and the excretion of calcium (Ca) and phosphate (P) in 15-h urine in zinc-deficient rats.

Male SD rats (150±10g) were used. They were kept in individual cages and fed zinc-containing (10 mg/100g diet; Pf group) or zinc-deficient (ZnD group) diets for 4 weeks. After 4 weeks, the BMD of the femur assessed by DXA was significantly lower in the ZnD group compared with the Pf group. The ALP level, a measure of osteoblastic activity in the femur, was significantly lower in the ZnD rats. The TRAP level, a measure of osteoclastic activity, was the same in both groups. The urine volume collected in a metabolic cage for 15 h was significantly lower in the ZnD group at 4 weeks. The urine Ca concentration did not differ between the two groups, but the mean urine P concentration was 1.535 and 0.025 mg/dl/mg creatinine in the ZnD and Pf groups, respectively. The urinary P excretion was significantly higher in the ZnD rats (p=0.0049). The results suggest that reduced BMD in zinc-deficient rats is related to increased urinary P excretion and decreased osteoblastic activity.