Study of Histomorphometric Changes of the Mandibular Condyles in Neonatal and Juvenile Rats after Administration of Cyclophosphamide

摘要

Forty 1-week-old Sprague-Dawley rats were divided into 4 groups of 10 animals each. Five rats of each group served as the controls, and another 5 were given weekly intraperitoneal injections of 20 mg cyclophosphamide (CTX, Endoxan, Cytoxan) per kg of body weight. The animals of each group were sacrificed either at 1 3, 5, or 7 weeks after initial intraperitoneal injection of CTX or water. The mandibular condyles of all rats were assayed histomorphometrically for changes on cartilage and bone cells, and other elements. The results showed a decreasing tendency in the thickness of the cartilage layer, the number of prechondroblasts, the number of chondrocytes, the percentage of cartilage matrix, the percentage of hard tissue, the bone surface perimeter, the number of osteoblasts, the number of osteoclasts, and the average number of nuclei per osteoclast in the condyles at 1 or 3 weeks after initial CTX treatment. After 7 weeks of treatment with CTX there was a significant decrease in the thickness of the cartilage layer, the number of prechondroblasts, and the numbers of both osteoblasts and osteoclasts per square millimeter of bone surface in the condyles, when compared with those of the control groups. In addition, after 5 or 7 weeks of CTX treatment there was a significant decrease in the percentage of hard tissue, the number of osteoblasts and the number of osteoclasts. Furthermore, changes in the morphology and size of the bone cells were also observed in all the rats. The reduction of the thickness of the cartilage layer was due mainly to a marked decrease in the* number of proliferative chondrocytes and the percentage of the cartilage matrix. All these findings demonstrated that a treatment of 20 mg CTX per week for 5 or 7 weeks had a cumulative effect which inhibited bone formation and affected both normal mandibular growth and facial profile in the juvenile rats. The cytotoxic effect of CTX also exerted an influence on the mitotic division of bone cells and the trabecular volumetric density of the madibular condyle.