. Calcified tissues; proceedings. Bone; Collagen; Calcification. 246 J. A. Fernandez de Valderrama, L. M. Munuer;- 1. Cortisone alone Using high doses of cortisone acetate (15 to 25 mg/kg), our observations, although inter-related, fall into four main categories. 1. In the first place, cell division is diminished or ceases. No new bone is laid down in the cortex, and in growing animals the production of metaphyseal bone is almost stopped when doses of 25 mg/kg are used. In the growth cartilage the pro- liferative zone is smaller than normal, and the enlarging zone wider. The cells in the enlar
. Calcified tissues; proceedings. Bone; Collagen; Calcification. 246 J. A. Fernandez de Valderrama, L. M. Munuer;- 1. Cortisone alone Using high doses of cortisone acetate (15 to 25 mg/kg), our observations, although inter-related, fall into four main categories. 1. In the first place, cell division is diminished or ceases. No new bone is laid down in the cortex, and in growing animals the production of metaphyseal bone is almost stopped when doses of 25 mg/kg are used. In the growth cartilage the pro- liferative zone is smaller than normal, and the enlarging zone wider. The cells in the enlarging zone do not reach the stage of complete hypertrophy, and at the base of this area a horizontal layer of bone is formed. In the metaphysis the number and calibre of the vessels is greatly decreased. 2. In the early stages there is resorption of bone, particularly in those regions where turnover is normally the most rapid. Osteoclasts may be seen on almost every bone surface (Fig. 1), and in the cortex some sinusoids appear to be irregularly. r Fig. One week after the administration of cortisone some sinusoids are di surfaces numerous osteoclasts are seen tiie resorbing bone enlarged. With high doses osteoclast formation and consequent bone resorption continue until no more osteoblasts and osteoblast precursors are left to coalesce into osteoclasts. In electron microscope photographs of the resorbing bone, all the matrix components appeared to be degraded simultaneously. This is in contrast to the resorp- tion seen in disuse osteoporosis (Valderrama and Little, 1965) where the non- collagenous matrix components dissapear first, and the collagen later. Even at some distance from the bone there is a tendency for osteoclast-like cells to form around sinusoids. 3. As bone resorption takes place and proliferation ceases the tissue is replaced by an irregular fatty marrow network, even in the Volkman's canals. By 21 days very few osteoclasts could be seen (their half-life is rathe
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