Low-calcium/high-phosphorus rickets in rats. II. Osteoclast changes

Weanling rats were given a low Ca (0.003%)/high P (0.64%) diet with and without vitamin D for periods up to 6 weeks. An ultrastructural examination of selected areas of the proximal tibial metaphysis was carried out to study osteoclasts and their relation to calcified and uncalcified bone tissue. Osteoclasts were seen with ruffled borders adjacent to unmineralized osteoid or with their processes penetrating small patches of calcified osteoid tissue. In both cases the calcified bone margin had a 'frayed edge', suggesting that osteoclasts are capable of chemical demineralization, as well as phagocytic action. In a few cases, osteoblasts were seen adjoining osteoid seams with underlying calcified bone exhibiting frayed edges indicative of demineralization. Osteoclastic intranuclear inclusion bodies similar to those found in experimental lead poisoning were observed. It was considered that the presence of a frayed, calcified bone margin at a considerable distance from the osteoclast supports the proposition that the initial action of this cell is to demineralize calcified bone.