Intestinal absorption of fluoride at high luminal concentration of fluoride

The paper reports that high fluoride concentrations in the intestinal lumen hinders the absorption of this anion. This conclusion was verified with th ree different experimental models. Pharmacokinetic experiments done in human volunteers revealed that the bioa vailability of fluoride from sodium fluoride (NaF, CAS 7681-49-4) enteric c oated tablets was 33% of that of plain (immediate release) tablets. The latter Endings were confirmed in rats receiving 1 ml of NaF solutions ( 40, 80 or 160 mmol/l) by gavage. The greatest AUC (area under the curve of fluoremia as a function of time) was obtained with an oral dose of 80 pmol of NaF This parameter was significantly greater (p < 0.01) with 80 <mu>mol than with 40 pmol NaF, but similar to that observed with 160 pmol. Fecal fl uoride excretions tin the 24 h following a single dose of NaF) and the bone fluoride contents (found at the end of 30 days of treatment with 40, 80 or 160 mu mol NaF/day), agreed with the AUC values. The rate of fluoride absorption (v, mu mol/10 min) through the intestinal w all was investigated with perfused, isolated rat duodenum in vivo. Fluoride absorption increased between 0 and 10 mmol/l luminal fluoride and decrease d with higher concentrations. Oxygen consumption of duodenal tissue decreased exponentially between zero (1.12 mu mol O-2 min(-1) g(-1)) and 10 mmol/l fluoride (0.45 mu mol O-2 min (-1) g(-1)).