Dietary NaCl loads promote calciuria and bone loss in adult oophorectomized rats consuming a low calcium diet.

This study was undertaken to determine whether dietary supplements of NaCl would exaggerate osteopenia in oophorectomized (OOPX) rats consuming a low calcium (0.01% Ca) diet. Thirty 300 g OOPX rats with 45Ca-labeled bones were studied. Animals in group 1 were killed at the start of the experiment, whereas those in groups 2 and 3 were fed a low calcium diet for 2 months. Group 3 rats received NaCl (8 g/100 g diet). Salt increased the urinary excretion of sodium, calcium, phosphate, cyclic AMP, 45Ca and hydroxyproline but did not augment fecal excretion of calcium or 45Ca. Salt caused bone loss. The femora of NaCl-treated rats contained less 45Ca, less calcium, less phosphate and less mineral ash than those of rats killed at the start of the experiment. It is suggested that in OOPX rats consuming a low calcium diet, increased NaCl intake causes decreased renal tubular reabsorption of calcium and consequently lowered plasma Ca++. This results in stimulation of parathyroid hormone secretion and thus increased bone resorption. We conclude that NaCl supplements exacerbate osteopenia in adult OOPX rats consuming a low calcium diet. The effects of high dietary salt intakes on bone loss in postmenopausal women deserve further study.