Comparative study of the effect of sodium fluoride and sodium monofluorophosphate on glucose homeostasis in the rat.

The effect of acute and chronic administration of sodium fluoride (NaF) or sodium monofluorophosphate (MFP) on the glucose homeostasis of the rat are compared. The oral administration of a single dose of 40 mumol/100 g b.w. of either compound produced similar increases in plasma glucose (up to 1.8 g/l) and diffusible fluoride (up to 130 mumol/l). In long-term experiments (three months of duration), treatment with NaF (a 5 mmol/l solution as the water supply) produced, in the first month of experiment, abnormal glucose tolerance tests and increased plasma diffusible fluoride levels (range: 2-12 mumol/l). Treatment with MFP, on the other hand, did not affect glucose homeostasis; plasma diffusible fluoride was always below 2 mumol/l. The results of these experiments indicate that glucose homeostasis is affected when plasma diffusible fluoride exceeds 5 mumol/l. The basal and glucose-stimulated insulin secretion of isolated Langerhans rat islets (incubated with solutions containing 2, 5, 10 and 20 mumol/l NaF) was significantly inhibited by 5 to 20 mumol/l fluoride. No effect was observed under similar conditions with MFP at concentrations of 2, 5, 10, 20 and 50 mumol/l.