Fluoride Action Network


Reaction with methyl thiazolyl tetrazolium (MTT) was used to investigate in vitro stimulatory (hormesis) effects of sodium fluoride (NaF) on kidney cells collected from three-day-old Sprague-Dawley male rats. The cell cultures were exposed to incremental concentrations of NaF ranging from of 0 (control) to 160 ?mol/L and from 500 to 16,000 ?mol/L. The mean optical density (OD) ± SD decreased from the control value of 0.591±0.119 to a minimum of 0.468±0.065 at 20 ?mol NaF/L before returning to the control level near 160 ?mol/L. At 500 ?mol/L the OD was 0.545±0.066, after which it decreased monotonically to 0.387±0.046 at 4000 ?mol/L, with cell death being complete at 16,000 ?mol/L. These results indicate that 20 ?mol/L is the lowest concentration at which a stimulatory (hormesis) effect of NaF is observed in kidney cell cultures of very young rats. In addition, results of flow cytometry and RNA detection confirmed these MTT findings.