The influence of dietary sodium on bone development in growing rats

Abstract

The present study investigated the effects of dietary sodium on bone growth in young rats. Five-week-old rats were fed one of three different diets for 60 days: low sodium (NaCl, 0.32 g/kg diet), normal sodium (NaCl, 2.6 g/kg) and high sodium (NaCl, 20 g/kg). The proximal tibial metaphysis (PTM), the fifth lumbar vertebra (LV₅) and the middle part of the tibia shaft (TX) were analysed by bone histomorphometry. The expression of three osteogenesis genes, Runx2, osteopontin and osteocalcin, was determined by RT-PCR in bone samples from the skull. In both the PTM and LV₅, trabecular area and thickness were increased by the low-sodium diet, while the high-sodium diet decreased trabecular area in LV₅. Dynamic data revealed that sodium restriction increased bone formation parameters in the PTM and LV₅, but decreased bone resorption in LV₅. In TX, endosteal bone formation was enhanced by the low-sodium diet and depressed by the high-sodium diet compared to the normal sodium group. But there were no statistically changes in the cortical bone area of TX. Low-sodium intake significantly enhanced the expression of all three osteogenesis genes compared to the normal sodium group, while high-sodium intake suppressed osteogenic gene expression. Our results suggest that sodium restriction in growing rats promotes bone development by influencing both bone formation and resorption.

Keywords:

• bone formation
• bone histomorphometry
• dietary minerals
• sodium
• rats

Acknowledgements

Appreciation is expression to the co-workers of the Guangdong Medical College and of the Chinese University of Hong Kong for assistance with data analyses. This research is supported by the National Natural Science Foundation of China (Grant No. 30971172), the Planned Science and Technology Project of Guangdong Province, China (Grant No. 2010 B050700022) and the Planned Science and Technology Project of Dongguan, Guangdong Province, China (Grant No. 2010 10815207).