Effects of high-phosphorus and/or low-calcium diets on bone tissue in trained male rats

The aim of the present study was to investigate if wheel running exercise could offset the detrimental influences of independent or combined high-phosphorus and low-calcium diets on bone tissue in rats.

Forty male dark Agouti rats were randomly assigned to eight groups of five animals. Four sedentary groups (SED) and four voluntary trained groups (TR) were fed over 6 wk of either a standard food or a modified diet, namely, high phosphorus (HP), low calcium (LCa), or high phosphorus combined with low calcium (HP/LCa). After sacrifice, blood samples were collected to determine parathyroid hormone, Ca(2+), and Pi levels. Both tibiae were removed for bone mass determination and extended histomorphometric analyses.

In SED rats, all unbalanced diets induced a sizeable bone volume decrease, up to 56%. Interestingly, steady training partially compensates for this bone volume loss, regardless of the considered modified diets. At the cellular level, only independent LCa diet induced a 38% decrease in osteoblastic surface in both SED and TR rat groups, generating thereby a reduction in bone neosynthesis. In terms of osteoclastic surface, an increase in this parameter was evidenced only in HP diets (both HP and HP-LCa), implying heightened bone resorption. The major effects of unbalanced diets are mainly observed on bone tissue because serum parameters (parathyroid hormone, Ca(2+), and Pi levels) remained only slightly modified.

Training induced a positive effect on unbalanced diet-altered bone tissue formation but remained inadequate to reach standard bone mass measured in SED rats fed with balanced food. Further, we suggest that the nature of the diet influences the balance between bone formation and resorption: LCa diet decreases bone formation, whereas HP and HP-LCa increase bone resorption.