Comparison Between Ovariectomy and Lactation Induced Bone Loss: A Dynamic Imaging Study

Introduction Lactation and postmenopausal osteoporosis are two hypoestrogenic physiological states that induce substantial changes in the bone mass and microarchitecture of women. During lactation, the body draws on calcium stores in the skeleton for milk production, resulting in substantial bone loss. In postmenopausal osteoporosis, ovarian hormone deficiency is responsible for bone loss. What is remarkable about lactationinduced bone loss is that bone mineral density and structure are rapidly restored after weaning when estrogen levels return to normal. In contrast, estrogen replacement post menopause can no longer reconstitute the deteriorated skeleton in the manner that occurs in lactating women after weaning. Therefore, reversible changes in bone during lactation and weaning may provide important insight into pathogenesis and treatment of estrogen-deficiency induced bone diseases. A past study comparing lactating and ovariectomized (OVX) rats found that the resulting loss of bone in both groups followed similar patterns; however, lactation had a greater effect on trabecular bone loss than ovariectomy. The purpose of this study was to explore the differences in structural mechanisms of bone loss and bone remodeling activities during lactation and postmenopausal osteoporosis in a rat model using high resolution in vivo micro computed tomography (μCT). We hypothesized that both types of bone loss would be caused by increased resorption, leading to rapid structural deterioration.