Calcium deficiency, pregnancy, and lactation in rats. Microscopic and microradiographic observations on bones.

Adult female rats were subjected to a calcium-depriving regimen (calcium-deficient diet containing oxalate + pregnancy + lactation) to obtain maximum bone mineral mobilization in as short a time as possible. The femur and tibia were investigated by histological, microradiographic and fluorescent microscopic methods. The regimen caused osteoporosis, which varied in severity with the degree of calcium deprivation. Most of the bone tissue removed was taken from the metaphyseal trabeculae and from the endosteal surface of the diaphysis. The remaining bone tissue seemed unchanged. The cells responsible for the bone removal did not seem to be multinucleated osteoclasts, but mononuclear, hypertrophied, elongated cells, possibly derived from the "resting" osteoblasts normally lining the bony surfaces. No signs of osteocytic osteolysis were observed. Bone formation was reduced, but present even in the most calcium-deprived animals. No increase in the amount of osteoid was observed.