Influence of gastric acidity on fluoride absorption in rats

The rate of F absorption from the stomach is pH-dependent, with greater absorption at low pH. Since the rate of absorption is also strongly influenced by the rapidity of gastric emptying, we have compared the relative importance of gastric acidity and gastric emptying in overall F absorption. Male rats (350 g, n = 85) were pre-treated with cimetidine (to inhibit gastric acid secretion) or pentagastrin (to stimulate gastric acid secretion) or were untreated controls, and given 50 micrograms F by stomach intubation. The pH of the F-containing solution was varied in the cimetidine-pre-treated group (pH 1.5, 5.5, 8.5), and was 5.5 for the control and pentagastrin-pre-treated groups. Gastric emptying was measured by addition of 14C polyethylene glycol to the F solution as an unabsorbed marker of fluid movement. F absorption was measured after 10, 20, and 40 min. The rate of gastric emptying was unaffected by pre-treatment or pH of the intubating solution. Initially, F absorption was greatest at low pH. After 40 min, absorption was comparable in all groups, averaging approximately 70% of the initial dose. The extent of absorption from the stomach was inversely related to pH, but increased absorption from the small intestine compensated for the low gastric absorption at high pH.