Abstract
To examine the effects of zinc on bone formation by endochondral ossification at growth stage, forty 5-week-old Wistar male rats, corresponding to childhood in humans, were randomly divided into 4 groups. In the control group, rats were fed on a standard diet. In the experimental groups, the rats were fed on no-zinc-component (zinc-deficient) diet, 50%-low-zinc diet and 150%-high-zinc diet respectively. After 4 weeks of feeding, all the rats were sacrificed and their condyles were observed as follows. In the densitometric measurement, the zinc-deficient group showed the lower value than the other three groups (p<0.01). In the microanalysis, there was a significant difference in the content of Ca or P between the zinc-deficient group and the other three groups (p<0.01). The high-zinc group showed the significantly higher content of Ca and lower content of P than the other three groups (p<0.01). Compared with the control group on the histopathological findings, the zinc-deficient group showed the decreased cartilage cells in resting zone and zone of proliferation with the deformed shape. In zone of hypertrophy appeared the decreased calcified matrix, which were surrounded by the increased cartilag cells. The erosion of calcified matrix by the multinuclear chondroclasts tended to decrease. In zone of subchondral bone formation appeared the thinner trabeculae. Compared with the zinc-deficient group, the low-zinc group showed the increased erosion findings of the calcified matrix, surrounded by the increased hypertrophic chondrocytes, could be observed frequently. The subchondral bone formation was improved, but the trabeculae were thinner. Compared with the control group, the high-zinc group showed the increase of both the calcified matrix surrounded by the hypertrophic chondrocytes and the erosion of the calcified matrix by the increased chondroclasts could be often seen. In zone of subchondral bone formation the differentiation of chondrocytes into bone cells was improved, leading to the successive and thick bone trabeculae in a vertical arrangement. Compared with the control group on the scanning electron microscopic findings, the zinc-deficient group showed the thinner bone trabeculae and the decrease of the longitudinal matrix in cartilage lacunae, on the wall of which appeared the calcareous globes in a sparse arrangement and the collective collagen fibers. On the surface of bone matrix formation, collagen fibers arranged sparsely and were in an irregular alignment, where the calcareous microdepositions were present. The low-zinc group showed the thickker bone trabeculae than the zinc-deficient group. In the cartilage lacunae arranged the uncalcified globes, where the collagen fibers were often seen crossed into networks. On the bone formation surface appeared many collagen fiber bundles in a regular alignment, and on the superficial part the collagen fibers were clearly seen crossed into networks, the same as the findings in the control group. Upon the examination of an overall image in the high-zinc group, compared with the control group, the cartilage development from the growing cartilage layer to the following thick bone trabeculae was improved. These results suggested that zinc, an essential trace element, had a positive effect on bone formation by endochondral ossification in the condyles of the growing rats.
