Ovariectomy-associated changes in bone mineral density and bone marrow haematopoiesis in rats

Abstract

The relationship between the bone mass loss and bone marrow haematopoiesis in osteoporosis remains obscure. We selected 3-month-old female Sprague-Dawley rats and randomly divided them into six groups. Three groups were ovariectomized (OVX), while the other three groups were sham operated (Sham). Four, 8 and 12 weeks after the surgical procedure, the rats were euthanized and sampled. The left femur was used for measurement of bone mineral density (BMD). The right femur distal metaphysic cancellous bone was processed for morphological evaluation. Our results showed that the femur BMD in the 4-week OVX group was not significantly decreased compared with that of the 4-week Sham group, but that the volume of adipose tissue in the bone marrow was markedly increased. The femur BMD in the 8-week OVX group was decreased significantly compared with that of the 8-week Sham group (P < 0.05). Meanwhile, the volume of haematopoietic tissue decreased and the volume of adipose tissue increased. The number of megakaryocytes was decreased (P < 0.05). Interestingly, the osteoclasts and mast cells were increased in number in the 8-week OVX group (P < 0.05). These changes became obvious in the 12-week OVX rats, in contrast to the Sham groups. The volume of trabecular bone and the number of osteoblasts in the 12-week OVX group decreased significantly. Increased reticulin fibres were observed only in the 12-week OVX group. Our studies demonstrated a reciprocal correlation between bone-forming osteoblasts and marrow adipose tissue and suggest that OVX rats may be valuable as an animal model to study hypohaemopoiesis.

Figure 1

Changes in haematopoietic tissue in OVX rats (H–E stain, 10 × 10). (a), (c) and (e) correspond to bone marrow sections of Sham rats at 4, 8 and 12 weeks and show the hypercellularity and sporadic scattered adipose tissue; (b), (d) and (e) correspond to the bone marrow of OVX rats at 4, 8 and 12 weeks and show the hypocellularity and the increase in adipose tissue. (e) The trabecular bone was arranged regularly with a dense network in Sham rats at 12 weeks; f, volume of decreased trabecular bone and increased free trabecular ends.

Figure 2

Changes in the reticulin fibres in the 12-week Sham and OVX rats (Gomori stain, 10 × 40). (a) The reticulin fibres were not increased in bone marrow in 12-week Sham group; (b) an increase of reticulin fibres in local bone marrow volumes in 12-week OVX group of rats.

Figure 4

Changes in the mast cells in the 8-week Sham and OVX rats (Toluidine Blue stain, 10 × 40). (a) Few mast cells (arrowheads) were observed in the bone marrow in Sham rats, and those observed were scattered in the marrow; (b) the mast cells (arrowheads) were increased in number as well as in granularity in the OVX rat marrow.

Figure 3

Changes in the osteoclasts and osteoblasts in the 12-week Sham and OVX rats (H–E stain, 10 × 10). (a) The number of osteoclasts (arrowheads) was increased in the bone marrow in OVX rats; (b) the osteoblasts (arrowheads) were easily observed in the bone marrow of Sham rats.