DUAL-ENERGY X-RAY ABSORPTIOMETRY OF THE RAT - ACCURACY, PRECISION, AND MEASUREMENT OF BONE LOSS

Dual-energy x-ray absorptiometry (DEXA) is now an established method o f measuring bone mineral density (BMD) in humans. We have applied the technique to measuring BMD in the rat. The short-term precision of the technique was assessed by calculating the BMD coefficient of variatio n at the rat spine (1.20%), total femur (0.52%), proximal femur (1.16% ), midfemur (1.00%), distal femur (0.96%), and proximal tibia (2.2%). The long-term precision of femoral measurements in rat cadavers over a 4 week period was 0.72% for the total femur and 1.2% for the distal f emur. The accuracy of the technique was assessed by comparing DEXA-mea sured bone mineral content (BMC) in vitro and in vivo with ashed BMC. Results indicated a highly significant positive correlation between in vitro DEXA measurements and ash BMC (r = 0.99) and between in vivo DE XA measurements and ash BMC (r = 0.89). The ability of the technique t o detect bone loss was assessed at the femoral site by comparing the B MD of ovariectomized (OVX) and sham-operated rats at baseline and at a 1 month follow-up. There was no significant difference in BMD between the groups at baseline. However, at 1 month follow-up the OVX group s howed a significant (p < 0.001) decline in BMD at the distal femur (-8 .6%) and in the total femur (-4.8%) compared with sham-operated rats. A comparison of retired breeder female rats with age-matched nulliparo us rats indicated that the BMD of retired breeder rats was significant ly lower than that of virgin females at all femoral sites (p < 0.01). The results suggest that the DEXA technique has the precis on and accu racy necessary to study changes in rat BMD. Furthermore, the technique can be used quickly and noninvasively to detect a bone loss following ovariectomy in the rat, and the distal femur may be an optimal site f or detecting such a bone loss.