Effect Of Estrogen On Alveolar Bone Remodeling In Osteoporotic Rats

This experiment investigated the effects of estrogen on alveolar bone remodeling in osteoporotic animal. SD-strain female rats were ovariectomized to set up osteoporosis model. The expressions of BMP and IL-I in alveolar bone remodeling of estrogen-stimulated ovariectomized (OVX) rats were analyzed by histological observation and immunohistochemical staining, the apoptotic cells were also observed by TU7NEL method. The tooth sockets were remained un-healed two months after tooth extraction in osteoporosis group; whereas, in the group with estrogen replacement therapy, the bone defects were filled with new bone one month after tooth extraction, the new bone matured after two months. Histological observation, after two months, showed that the newly formed bone transformed into matured bone with bone marrow and regular bone trabeculars, and there is no obvious boundary between the new bone and the old bone. In osteoporosis group, the positive IL-i immunoreactivities were mainly located in the osteoclasts, some of the osteoblasts and osteocytes were also -4- positively stained. The positive reaction was obviously decreased in the estrogen-replaced OVX rats. BMP in the alveolar bone of estrogen-stimulated group was expressed intensively. Positive reaction of BMP immunostaining was mainly located in the osteoblasts and the adjacent undifferentiated mesenchymal cells, while in the osteoporosis group, expression of BMP was obviously decreased. Few apoptotic osteocytes were detected in the osteoporosis group, while apoptotic osteoblasts were incidental detected and typical apoptotic osteoclasts were not found. A prominent apoptosis in osteocytes and few of apoptotic osteoblasts and osteoclasts were detected both in the normal (control) group and in the estrogen-replaced group. Histological observation confirmed that alveolar bone remodeling in estrogen- replaced group was obviously faster than that in osteoporosis group. Estrogen play an active and promotional role on alveolar bone remodeling and repairing. Immunohistochemical staining showed that the immunoreactivity of BMP was strong in the majority of estrogen-replaced group and was weak in the minority of the same group. The results indicated that there is a relationship between effect of estrogen on alveolar bone remodeling in treating osteoporosis and promotional effect of estrogen on BMP in alveolar bone. Estrogen deficiency might induce increased secretion of IL-i, consequently, IL-i participated in bone resorption during alveolar bone remodeling. IL-i expression -5- can be altered by estrogen replacement therapy, which is contribute to remodeling of osteoporotic alveolar and repairing of bone defects. Results of TUNEL staining indicated that in normal physiological condition, estrogen could inhibit bone resorption by promoting apoptosis of osteoclasts, thereby maintain the balance of bone metabolism. On the contrary, apoptotic velocity of osteoclasts is slowered due to the weakened effect of estrogen on regulating osteoclasts apoptosis in the condition of estrogen deficiency. The number of osteoclasts increased while it抯 life span is relatively increased too, it would finally conduce to strengthening of the bone resorption activity of osteoclasts. The metabolic velocity of bone can be s...