Metabolic turnover of fluoride by the skeleton of the rat.

The turnover of skeletal fluoride, a process which involves the acquisition and elimination of fluoride by bone, has not been completely studied. This topic is of current interest in relation to the programs of fluoridating communal water supplies as a means of partial control of dental caries in the human (1). Skeletal tissues have a marked affinity for fluoride and the bones are known to accumulate fluoride when the intake of the element is increased (2, 3). Balance studies carried out with young human adults showed no significant retention of fluoride when the intake was 0.5 to 1.0 mg. (4) or 4.0 to 5.0 mg. (5) per day. Since the normal fluoride intake in regions of low fluoride-bearing waters can hardly exceed 1.5 mg. per day (4, S), the results of the balance studies do not account for the observation that the fluoride content of the bones of the human increases progressively with age (2). The only published study contributing significantly to the question of the rate and degree of elimination of skeletal fluoride is that of Glock et al. (2). These workers used rats which had been fed a ration containing over 200 parts per million of fluoride for 32 and 40 weeks. After withdrawal of the high fluoride-containing ration the fluoride concentration (i.e. per cent fluoride) in the fat-free long bones decreased markedly and progressively over a period of 14 weeks. Since Glock and coworkers recorded the data of fluoride analyses of the bones in terms of concentration rather than as in the absolute amount of the element present in a given bone, it can be understood that their results were influenced by skeletal growth as ,well as by actual elimination of fluoride from the skeleton. That is, skeletal accretion would have the effect of diluting the fluoride present in the skeleton, with the result that a decrease of concentration