Novel approach for pathogenesis of osteoporosis in ovariectomized rats as a model of postmenopausal osteoporosis.

Obesity and osteoporosis are two chronic conditions that have been increasing in prevalence. Menopausal transition years place women at high risk for visceral obesity as well as osteoporosis. This study was carried out to elucidate the effect of visceral adiposity on ovariectomy-induced osteoporosis in rats.We studied female Wistar rats aged 12-14 months, divided into four groups: a) Sham-operated control (SHAM) rats (n = 12), rats were fed a control diet (59% of food intake from carbohydrates, 7% from fat, 21% from protein, 13% from minerals and ash) for 12 weeks, b) High fat diet-fed control (HFD) group (n = 9), rats were fed a high fat diet (49% of food intake from carbohydrates, 17% from fat, 21% from protein, 13% from minerals and ash)for 12 weeks, c) Ovariectomized (OVX) rats (n = 14), rats were fed a control diet as SHAM rats, d) High fat diet- fed ovariectomized (OVX- HFD) rats (n = 13), rats were fed a high fat diet as HFD group. At the end of the experiment, blood samples were collected for calcium, phosphorus, and alkaline phosphatase (ALP) assays. Unilateral left perirenal fats were surgically removed and weighed. Specimens from right perirenal fats and tibia were isolated and processed for histological examination. Histomorphometric analysis of the tibia and visceral adipose tissue was also performed.OVX, HFD, and OVX-HFD rats showed a significant increase in relative visceral fat weight, and plasma ALP, and a significant decrease in plasma calcium, and phosphorus levels compared to SHAM rats. Light microscopic examination of the tibia of the OVX rats revealed a significant decrease in the cortical bone thickness (CBT) and the trabecular bone thickness (TBT), and a significant increase in bone marrow adipose tissue compared to SHAM rats. In addition, there was a significant increase in the osteoclast number, and a significant decrease in the osteoblast number. The changes in bone marrow adipose tissue as well as osteoclast number were further accentuated in OVX-HFD groups.Visceral obesity played a crucial role in the development of osteoporosis in ovariectomized rats through effects that might involve both osteoblasts and osteoclasts.