Abstract
The purpose of this study was to gain more definitive information on the placental transfer of fluoride in rats at low maternal intake level.
Wistar rats (8 week-old) were used in this study, and they received a low fluoride diet (F=0.3 ppm) and distilled water. They were mated after being kept a week under the experimental conditions. Female offspring born from them were randomly assigned to nine groups with various levels of fluoride intake at 3 weeks of age. They received a low fluoride diet and 0-10 ppmF (as NaF) solution, or an ordinary breeding diet (F=33ppm) and tap water (F≅0.1 ppm). The nine groups were called the 0, 0.1, 0.2, 0.5, 1, 2, 5, 10ppm group, and tap water group. They were mated with male rats at 12 weeks of age. Females were killed immediately after delivery. Plasma and left femurs were obtained from 158 females, and plasma and tibiofemoral bones of the newborn pups were taken from each litter. Plasma inorganic fluoride and bone fluoride were analyzed with the electrode method following diffusion procedures. Total plasma fluoride in females was analyzed with the electrode method following ashing and diffusion procedures.
Close agreement was found between inorganic and total values of plasma fluoride in females. Plasma inorganic fluoride in females of the 0-1 ppm groups was constant, ranging from 2-4 ppb, but it rose from 4 ppb to 74 ppb in proportion to fluoride intake in the 1-10ppm and tap water groups. The fluoride in pups of all groups were ranging 2-6 ppb. Bone fluoride concentrations in adult females rose from 7 ppm to 763 ppm, and those in pups rose from 7 ppm to 56ppm in proportion to fluoride intake in all groups.
These findings suggest that (1) there is little organic fluorine in rat plasma, (2) plasma fluoride in rats may be maintained at a lead above about 3 ppb, (3) the amount of fluoride transferred to rat fetuses increases in proportion to fluoride intake even at low maternal intake levels, and (4) bone fluoride in newborn pups is an excellent index of the amount of fluoride transferred to fetuses.
