Fluoride absorption from disodium and calcium monofluorophosphates from the gastrointestinal tract of rats.

The contribution of the stomach and the small intestine to the in vivo absorption of fluoride from disodium and calcium monofluorophosphates was studied in comparison with that observed when sodium fluoride is given to rats. In vitro experiments with ligated duodena were also carried out. Fasted rats were given orally 50 micrograms of fluoride in pH 6.3 buffered disodium monofluorophosphate solutions with and without 50 mM added calcium. The same amount of fluoride was administered in the form of an aqueous sodium fluoride solution. In both cases the fluoride solutions contained trace amounts of (14C)-labeled polyethyleneglycol as a marker for the study of water movement through the gastrointestinal tract. Results obtained show the small intestine as the main site of the absorption of the studied compounds. Under the fasting conditions employed in our study gastric absorption was in turn, almost negligible. While fluoride transport from sodium fluoride seems to occur through a difussion mechanism, disodium and calcium monofluorophosphates appear to be absorbed through a more complex mechanism involving an enzymatic hydrolysis and an independent and possibly parallel direct tissue absorption of a soluble, neutral calcium monofluorophosphate complex.