Study On Bone Marrow Hematopoiesis And Bone Marrow Angiogenesis In Ovariectomized Rats

Objective:Osteoporosis is a systemic skeletal disease.Studies by some researchers suggested that a decrease in bone marrow volume associated with osteoporosis and age-related osteopenia is accompanied by an increase in marrow adipose tissue.Recently,some scholars presented the hematologic etiology of osteoporosis.They think the development of osteoporosis is related with the chronic bleeding.The ovariectomized rat is a widely used animal model for osteoporosis research in the medical field.The character of the osteoporosis is the bone mass decreased,so we defined the bone mineral density(BMD) as an index to evaluated the degree of osteoporosis and combined this observation with the bone marrow pathological examination to observe the bone marrow hematopoiesis and bone marrow angiogenesis.Thus far the relationship between the changes in BMD and bone marrow hematopoietic tissue remains unclear.In the present study,we used the OVX-rat as an animal model to examine the bone marrow pathology,and to explore the relationship between the changes in BMD and the bone marrow hemopoiesis as well as the bone marrow angiogenesis during the development of osteoporosis.Method:Thirty three-month-old female Sprague Dawley rats were randomly divided into ovariectomized(OVX) groups and sham operated(Sham) groups, and executed after 4 weeks,8 weeks and 12 weeks respectively.The left femur was used for measurement of bone mineral density(BMD).The right femur distal metaphysic cancellous bone was fixed in 10%formalin,daft calcium by EDTA-Na₂,dehydrated and embedded in paraffin,4μm-thick slices were obtained from the section and stained with haematoxylin-eosin(H-E) to observe the changes of the bone marrow pathology.Toluidine Blue stain(pH 3.8) to observe the mast cells.Using the eye-piece graticules to observe the volume of hematopoietic tissue,adipose tissue and trabecular bone resepectively,and to count the number of megakaryocytes,osteoblasts,osteoclasts as well as mast cells.The number of bone marrow microvessels was examined by means of immunohistochemical staining for CD34 to stain the endothelial cells of blood vessels to definite the bone marrow microvascular density(MVD).Plasma levels of vascular endothelial growth factor(VEGF) were examined by the method of ELISA.Results:The BMD of femur in OVX 4 weeks group was not descreased significantly compared with the Sham 4 weeks group,but the volume of adipose tissur was significantly increased.The BMD of femur in OVX 8 weeks group was descreased significantly compared with the Sham 8 weeks group(P＜0.05). Meanwhile,the volume of hematopoietic tissue decreased and the volume of adipose tissue increased.The number of megakaryocytes decreased(P＜0.05). However,the number of osteoclasts and mast cells were increased in bone marrow sections of OVX 8 weeks group(P＜0.05).Theses changes became obviously in OVX 12 weeks group rats bone marrow section.However,with only the increase of time,there have no significant changes in rats' femur BMD and bone marrow pathology.The volume of hematopoietic tissue,trabecular bone,adipose tissue,the number of megakaryocytes,osteoblasts,osteoclasts and MVD have on significant changes in Sham groups.There had a positive correlation between BMD and the volume of hematopoietic tissue or MVD as well as a negative correlation between BMD and the volume of adipose tissue. There had a positive correlation between the volume of hematopoietic tissue and the number of osteoblasts and MVD as well as a negative correlation between the volume of hematopoietic tissue and the number of osteoclasts.The plasma levels of VEGF in OVX group had no significant differences with that of the Sham group,and had no correlation relationship between the index of bone marrow pathology.Conclutions:A progressive loss of BMD accompanied with a decrease in the volume of hematopoietic tissue and MVD and an increase in the volume of adipose tissue. There has a reciprocal relationship between the bone-forming osteoblasts and marrow adipogenesis.The increase in the adipose tissue volume and the decrease in the osteoblasts and MVD may be the key to the decrease in hematopoiesis.