Fluoride balance and tissue concentrations: effect of dose frequency.

The possible effects of dose frequency on the bioavailability, balance and tissue levels of fluoride were determined using young adult rats. It was hypothesized that, because of the rapidly exchangeable pool of fluoride in calcified tissues, smaller and more frequent doses of fluoride would increase the retention of fluoride in the body. All groups were fed a low-fluoride, semi-purified diet throughout the six-week study. Group B received water with 25 ppm fluoride ad libitum. Groups C, D, and E received fluoride in amounts similar to that of group B but by ig intubation one or three times each day or by ip injection once each day. Group A received fluoride only in the food. Two 24-h fluoride intake and excretion determinations were made during each week. Plasma, enamel and femur epiphysis fluoride levels were determined at the end of the study. Compared with group B, the average fluoride absorption and balance values were 13% and 10% higher, respectively, in groups C, D and E. Plasma and calcified tissue fluoride levels were also slightly higher in the latter groups but, in general, the differences were not statistically significant. In the ip-injected group, the fecal excretion of fluoride was 96% greater than the amount ingested with the diet which indicated net intestinal secretion. It was concluded that, for a given level of intake, dose frequency has only minor effects on the absorption, balance and tissue levels of fluoride in the rat. The influence of the rapidly exchangeable calcified tissue fluoride pool on the general metabolism of the ion appears to be limited when intake occurs at least once each day.