Placental Transfer of Fluorine to the Fetus in Rats and Rabbits1

1.Various levels of fluorine were fed to rats (Sprague-Dawley and Wistar strains), and to rabbits, for varying periods of time in attempts to determine the permeability of the placenta to fluorine added as sodium fluoride to the basal diet. Passage of fluorine to the fetus by way of the dam’s milk was also studied in rats. In these experiments the placentae of the rats and rabbits were an extremely efficient barrier to the passage of fluorine. This effect may be related to the permeability of the placenta, to the molecular size of any compounds in which fluorine had become fixed, or it is possible that the transfer of fluorine may have been conditioned by other factors which affect placental transfer.2.Alkaline phosphatase activity of various tissues of rats and rabbits as affected by the diets containing various levels of fluorine was also studied. In these studies alkaline phosphatase activity of plasma, kidney, liver residue, intestinal mucosa and bone were not suitable criteria of the degree of fluorosis in rats and rabbits.3.Roentgenologic studies of the hind legs of the experimental rabbits were made. The roentgenograms did not reveal any abnormalities although excess growths of tissue were observed on the long bones of some rabbits fed high levels of fluorine.