Comparison of three methods for estimation of bone resorption following ovariectomy in the distal femur and the proximal tibia of the rat

The study of estrogen-deficient bone loss requires accurate assessment of b one resorption; however, there has been considerable variance in the values reported for this variable, We compared three techniques for estimating bo ne resorption in the adult rat at four anatomical sites, the metaphysis and epiphysis of the distal femur and the proximal tibia, The techniques inclu de an osteoclast-morphology-based method (VK-Oc), a bone-surface-based meth od (Pit-Oc), and an enzymatic method (AP-Oc), Thirty 6-month-old rats were either ovariectomized (ovx) or sham operated (sham) and killed at 0, 9, or 18 days postoperation, Each method was analyzed for variance in the ovary-i ntact groups and for the ability to detect the increase in osteoclast surfa ce known to occur following ovariectomy. A 50-fold variation for the estima tion of extent of osteoctast surface was entirely accounted for by these th ree methods for osteoclast estimation, The VK-Oc method was the most consis tent for discriminating levels of osteoclast surface between ovary-intact a nd ovariectomized rats, detecting an increase at three of the four sites. T here was no difference between the methods in their ability to produce cons istent values for ovary-intact groups. The Pit-Oc method produced the large st numerical difference between the two operation groups with a 2.5-3-fold increase compared with 1.25-1.5-fold for the other methods (p < 0.001). How ever, the greater variance associated with this method limited the ability to detect the increase in osteoclast surface following ovariectomy, The AP- Oc method lacked the sensitivity of the other two methods. The oophorectomy -induced increase of osteoclast surface in the metaphysis of distal femur w as larger and more consistently demonstrated than increases at the other si tes. (Bone 24: 597-602; 1999) (C) 1999 by Elsevier Science Inc. All rights reserved.