Using ovariectomized rats as an animal model of postmenopausal women, we examined the causal relationship between fluoride (F) exposure and the high risk of development of osteoporosis. In order to obtain the estrogen (Es) deficient animals, 5-week-old SpragueDawley rats, which were overiectomized at 3- and the 5-week-old female rats without ovariectomy were purchased. The overiectomized rats were divided into two groups: the Es deficient, and the combination of Es deficiency and F exposure groups. Also rats without ovariectomy were divided into two groups: the F exposure and the control groups. Rats of both the F exposure and combined groups were given free drinking water containing 1.0 mg/l F ions (NaF), while the control and Es deficient rats were given tap water. Three months later, the samples of calvaria were subjected to soft X-ray radiography and electron microscopy. In both the Es deficient and F exposed rats, soft X-ray radiography demonstrated an increase of radiolucent areas of the calvaria at a certain degree. However, this trend was prominent in combined group rats, resulting in the appearance of a labyrinthine pattern. In the tibia, light microscopy revealed a significant decline of trabecular architecture in this same group, suggesting the onset of osteoporosis. Electron microscopy demonstrated an increase of amorphous minerals in the radiolucent areas of the calvaria. However, we could not observe a significant increase of osteoclast number. From these findings, it appears that F exposure may accelerate the development of postmenopausal osteoporosis even at a low dose of F ions. Moreover, it is suggested that the primary cause of osteoporosis may result from a decline of the bone formation rather than excessive bone resorption. The animal protocol was approved by the Animal Care and Use Committee of Meikai University.
17 May 2014 - 20 May 2014