The effect of fluoride on nephrocalcinosis in rats.

To investigate the effects of fluoride on soft tissue calcification, female weanling rats were fed a nephrocalcinogenic diet and NaF in drinking water over a 4 week period. The diet contained adequate Ca (0.5%) and high phosphorus (1.0%, P). The nephrocalcinosis is attributed to the relatively low dietary Ca/P ratio since addition of Ca to provide a Ca/P ratio of 2.0 prevents kidney calcification. With NaF in drinking water at levels of 1.19 to 4.76 mmol/L kidney calcification was decreased from 127 +/- 24 to 17.3 +/- 1.7 mumol/g wet weight, with no significant differences over this dose range. With the increasing NaF doses, serum F, at 4 weeks, increased from 4.4 +/- 0.8 to 36.5 +/- 6.0 mumol/L compared to untreated F levels of 1.2 +/- 0.1 mumol/L. Bone histology showed no evidence of F stimulation with any of these NaF doses. Previously reported work has shown that, for weanling rats on this diet, greater than 4.8 mumol/L NaF in drinking water is required to produce histological fluorosis within 5 weeks. To inhibit kidney calcification, NaF treatment must be maintained throughout the 4-week study period since calcification occurred if NaF was withheld over either the initial or final 2-week period. These findings indicate a possible therapeutic value of NaF, clinically, in the prevention of soft tissue calcification.