The Regulation Of Epiphyseal Growth Plate Growth And Fusion By Estrogen

【Objective】 This study is designed to explore the mechanisms of estrogen regulating growth and fusion of the epiphyseal growth plate on ovariectomized New Zealand White rabbits.【Methods】 The rabbits received either 140μg/kg body weight estradiol benzoate (E2 group) or vehicle (NE2 group) i.m.4 weeks after ovariectomy. (1)The estradiol levels of the plasma and the histological changes of the uteri were studied; (2)The growth rates were determined by radiographs on the femora every 2 weeks, the final lengths of the femora and tibia were measured at the end of the study (29 weeks of age); (3)The quantitative histology evaluations on the femora and tibia were performed by light microscope to determine the timing of growth plate fusion; (4)The ultrastructural changes of the chondrocytes of the rib growth plate were assessed to explore the effects of estradiol on the proliferation, differentiation and physiological cell deth.【Results】 (1)The estradiol levels of E2 group were achieved to the levels of normal female rabbits with the normal development of uteri during the study; (2)The femora growth rates of E2 group were greater than that in NE2 group during the early stage of the study (20 weeks of age), which were declining within the middle or later stage of the study; (3)During the middle or later stage of the study the growth plates of the femora and tibia fused in E2 group; (4)By the end of the study, there were more dark chondrocytes within the rib growth plate in the E2 group rabbits. The intracellular lipid accumulations were also found in the hypertrophic chondrocytes of E2 group, with high numbers of expanded rER and vacuoles.【Conclusions】 Estrogen can cause the growth, senescence and fusion process of the growth plate during the sex maturation.(1)The New Zealand White rabbits ovariectomized during the juvenile (12 weeks of age) can be used as animal model for studying the effects of estrogen by the injection of estradiol.(2)After the injection of estradiol, the femora growth rates of the E2 group were increased until the middle stage of the study; (3)The data showed estrogen may regulate the proliferation, differentiation and aberrant physiological death of the chondrocytes in the growth plate.