Ninety‐sixth annual meeting. Program and abstracts

Lactation will reduce the stores of bone mineral irrespective of the amount of dietary calcium. In the rat, mineral requirements for lactation are met primarily by remodeling the cancellous bone in the metaphyses of long bones. Fluoride, by the nature of its incorporation into bone crystals and by its direct cytotoxic effect on bone resorbing cells, reduces the availability of calcium from bone. The purpose of the present study was to determine the effects of fluoride ingestion and multiple pregnancies and lactations on the morphology of the rat femur. Virgin female Sprague-Dawley rats were given a standard laboratory diet and 150 ppm fluoride in the drinking water ad lib. while undergoing three successive pregnancies and lactations. Rebreeding periods commenced immediately following a 21-day lactation period. All litters were normalized to 8 pups on the day of birth. Following the third lactation period, both femurs were removed from all animals and prepared for either light or scanning electron microscopy. Periosteal surfaces of the diaphysis consisted of areas of woven bone formation with some prolonged resting areas around osteocyte lacunae. Endosteal surfaces consisted of areas of bone formation and resorption. Mineralized segments in formation areas were short and irregular in shape, and arranged in an unorganized manner. The irregular Howship's lacunae in resorption areas were located at various depths and sub-divided by prominent sharp ridges. The active resorption process exposed several layers of bone lamellae. The interior of the diaphysis was characterized by absence of an endosteal zone and by extensive bone loss from the intermediate zone by cavitation and remodeling in secondary Haversian systems. Distal metaphyseal trabeculae were dominated b y large areas of active resorption. It appears that fluoride ingestion during lactation created a heightened state of calcium homeostatic stress. Consequently, additional bone mineral was mobilized by resorption of the interior and endosteal surfaces of the diaphysis.