Excretion, serum, bone and kidney levels of F in rats after a high single dose of F and Mg + F.

The aim of this study was to clarify the mechanisms by which Mg protects the organism against the acute toxic effects of F. A single dose of F (30 mg F/kg as NaF) was given to young rats by gastric gavage with or without a prior dose of Mg (as MgCl2) equivalent to the F dose given (groups MgF and F, respectively). Feces and urine, serum, femoral bone and kidney were sampled 24 h after the doses were administered. Mg given 30 min before fluoride did not modify elevation of the F content in serum or in femoral bone when each was measured 24 h after the F dose. Except for fecal excretion of F, Mg did not significantly influence F excretion. However, the mean renal content of calcium, which was highly elevated by F alone, was markedly less in the MgF group. The renal content of Mg was at almost the same level in the MgF group as in the controls. The antidotal effect of Mg against F toxicity cannot primarily be due to interference with the absorption of F. Prevention of the nephrocalcinotic effect of F by Mg appears to be a mechanism for reducing the acute toxic effects of F, but our results suggest that other tissue and intracellular mechanisms may be more decisive.