Abstract
It is known that the number of osteoclasts changes dramatically from birth to 20th day in femora of rats. It is therefore expected that osteoclasts must undergo change in character during this period of increasing osteoclasts. Cells were isolated from rat femora during the 10 days after birth. In this period the number of osteoclasts changed greately. The cells were studied on the kinds of cells and their morphology, the enzyme activities, the morphological response to hormones and the resorbing activity, with special interest in osteoclasts. The results were as follows. 1. The cells, which were isolated and adhered to glass on 1st, 2nd and 3rd days, were small globular cells, macrophage-like cells, osteoclasts and fibroblast-like cells. The cells on 5th day were small globular cells only. The cells on 7th day were similar in appearance to those on 1st day. The cells on 10th day were fibroblast-like cells mainly. The kinds of cells greately varied on 5th and 10th day. 2. In active staining method, acid phosphatase (ACP) activity was positive in osteoclasts and was slightly positive in macrophage-like cells and a few other cells on 1st day. On 2nd day this enzyme activity in osteoclasts was the highest of all days. The activities of malate dehydrogenase (MDH), succinate dehydrogenase (SDH) and lactate dehydrogenase (LDH) were the highest in osteoclasts of all cells. MDH activity was highly positive and was higher than the other dehydrogenases. The activities of three dehydrogenases on 3rd day were the lowest of all days. They regained the initial levels on 5th day. SDH and LDH activities decreased again on 10th day. 3. Calcitonin (CT) induced the retraction of the edge in osteoclasts after 1hr of incubation. Fibroblast-like cells appeared on 3rd, 7th and 10th days. CT repressed these appearances. Parathyroid hormone (PTH) stimulated the appearance of osteoclasts markedly on 7th day. PTH increased the motility of osteoclasts in appearance. 4. Many resorbed areas appeared on the tooth slice with the cells isolated on 1st day on after incubation for one day. On 1st day the resorbed areas appeared in the same degree as those on 7th day. There were little or no resorbed areas in the case of the cells isolated on the other days. In scanning electron micropic appearances, osteoclasts were classified into three types : the cell on 1st day, on 3rd day, and on 5th, 7th and 10th days. From these results it was shown that the cells changed greately in kind and in number from birth to 10th day. Osteoclasts changed qualitatively in enzyme activities and response to hormone in age-related manner. Bone resorbing activity changed also along with these changes.
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