TEMPORAL CHANGES IN CANCELLOUS BONE-STRUCTURE OF RATS IMMEDIATELY AFTER OVARIECTOMY

To understand the structural changes accompanying estrogen deficiency- induced bone loss, we examined the temporal changes in cancellous bone structure in an animal model of postmenopausal osteoporosis. Matured rats were subjected to bilateral ovariectomy, and groups of eight anim als were sacrificed at 5-day intervals. Histomorphometric and trabecul ar strut analyses of the excised proximal tibia, and bone mineral dens ity measurement of the distal femur, were used to investigate cancello us bone loss as a result of estrogen deficiency. There was an immediat e increase in bone turnover after ovariectomy, as evidenced by rapid i ncreases in osteoclast surface (400%) and bone formation rate (270%). The resultant time-dependent decrease in cancellous bone volume was hi ghly related to a decrease in trabecular plate number and connectivity parameters, but was not related to the thickness of the remaining can cellous plates. Our results suggest that cancellous bone loss due to e strogen deficiency is the result of decreased connectivity, likely due to osteoclast perforation of trabecular plates, followed by complete removal of the plate without prior generalized thinning.