Reduction in bone formation and elevated bone resorption in ovariectomizedrats with special reference to acute inflammation

Changes in bone modeling and remodeling in the tibia of growing rats within 30 days of ovariectomy (ovx) were evaluated by histomorphometric, mechanic al, and biochemical means, Three days after ovx, suppressed bone formation was seen. This was shown by reduced osteoid volume, osteoblast surface, and bone formation rate in the secondary spongiosa, and a reduced longitudinal growth rate in the growth plate, In addition, the alkaline phosphatase and tartrate-resistant acid phosphatase activity in hone marrow supernatants w as suppressed in conjunction with elevated serum sialic acid levels, indica ting inflammation, Although estrogen deprivation itself may provoke the inf lammatory process, the serum sialic acid level in the ovx group returned to the baseline level within 5 days after surgery, while that of estradiol in the ovx group remained consistently lower. This suggests that surgical str ess, not estrogen deprivation, is the primary cause of the inflammatory res ponse shortly after ovx, A significant difference (p < 0.01) between the ov x and sham rats was seen in the osteoclast surface, which peaked on day 7 i n the ovx rats. On day 14 postovariectomy, the hone formation rate peaked a nd remained constant until day 30, In the ovx rats, there was a sustained r eduction in the serum albumin level until day 30, Estrogen deprivation may be the primary cause of these changes, because both surgical ovx and medica l oophorectomy with gonadotropin-releasing hormone agonist (GnRHa) reduce t he serum albumin level, In numerous studies dealing with changes after ovx in rats, we have observed: 1) a transient reduction in bone formation in re lation to inflammatory changes evoked by ovx surgery, and 2) a sustained re duction in the serum albumin level for at least 30 days after ovx that is p ossibly due to estrogen deprivation, (C) 2000 by Elsevier Science Inc, All rights reserved.