Biol. Pharm. Bull. 30(5) 898—903 (2007)

deficiency following menopause is by far the most common cause of age-related bone loss. Postmenopausal osteoporosis (POP) has become a major problem with significant morbidity and mortality. Bone loss induced by ovariectomy in rats has been widely used as a model of POP and has been validated as a clinically relevant model of this condition in human. Peripheral quantitative computed tomography (pQCT) and dual energy X-ray absorptiometry (DEXA) are non-invasive bone densitometry methods used in clinical settings for assessment of bone density as well as the efficacy of treatment for osteoporosis. pQCT provides measurement of volumetric bone densities (vBMD, total and cortical bone mineral density) as well as a set of geometric variables including cross-sectional area; while DEXA provides measurements of bone mineral content (BMC) and the area of the scanned region and areal bone mineral density. Although DEXA is one of the most commonly used clinical methods for measurement of bone mass, it is not ideal for use in animal studies and clinical trials due to its inability to distinguish between cancellous and cortical bone and provide limited information regarding bone architecture. In contrast, pQCT is now the method of choice as it can provide vBMD, differentiate cortical and trabecular bone compartments and perform in vivo measurement of histomorphometric parameters like endosteal and periosteal circumferences, total and cross-sectional bone areas. As an alternative to four-point bending testing, three-point bending testing has become more widely used for the evaluation of whole bone strength. Although the two testing modalities are complementary to some extent, when describing the mechanical characteristics of bone, it appears that four-point bending testing has some disadvantages, which requires that the force at each loading point be equal. This requirement is simple to achieve in regularly shaped specimens but difficult to achieve in whole bone tests. Therefore, three-point bending is used more often for measuring the mechanical properties of bones from rodents. The differential responses of bone properties to the midto long-term effects of ovariectomy in rats has been widely studied, and simultaneously efficacy testing of potential chemicals for anti-POP in ovariectomized (OVX) rats was also conducted in a duration of midto long time. Previous studies showed that the earliest statistically significant time of cancellous bone loss of rats in the proximal tibial metaphysis (PTM), lumbar vertebral body (LVB) and femoral neck (FN) occurring at 14, 60 and 30 d post ovariectomy, respectively, and the time of 50% bone loss for the PTM was 30— 60 d, and for LVB and FN was 180—270 d. While the earliest changes in cortical bone width and medullary cavity size to be between 90—120 d and to reach a steady state often 180 d or more. These suggested that influence of ovariectomy on bones showed siteand time-specific development. The research purpose and content of previous studies are very different from the present study. Previous studies investigated the long-term effects of ovariectomy or ageing on animal skeletons, furthermore, bone parameters studied were limited to bone mass and peak load in bone strength, neglecting bone morphological parameters, predicted bone strength parameters and other structural mechanical strength (including break load, deformation, energy). Thus, few systemic reports about the shortto mid-term effects of ovariectomy in appendicular bones of rats are available. Against this background, we investigated shortto mid-term effects of ovariectomy on bone turnover markers, bone mass, bone morphologic and predicted bone strength using a pQCT system, and 898 Vol. 30, No. 5