DIFFERENTIATING BETWEEN ORCHIECTOMIZED RATS AND CONTROLS USING MEASUREMENTS OF TRABECULAR BONE-DENSITY - A COMPARISON AMONG DXA, HISTOMORPHOMETRY, AND PERIPHERAL QUANTITATIVE COMPUTERIZED-TOMOGRAPHY

In studies of rat bone metabolism, trabecular bone density should be m easured. Three established methods of measuring trabecular bone includ e trabecular bone volume by histomorphometry (BV/TV%), trabecular bone density by peripheral quantitative computerized tomography (pQCT), an d areal bone density of trabecular-rich regions by dual x-ray absorpti ometry (DXA). We compared the ability of these three methods to discri minate between orchiectomized (orchidectomized) rats and controls. Six teen male Sprague-Dawley rats (400-425 g) were orchiectomized, and 16 others were controls. In vivo spine bone mineral density (BMD) was mea sured at the beginning of the study and again after II weeks. Rats wer e sacrificed, and ex vivo BMDs of the right femur and tibia were measu red by DXA, followed by trabecular bone density of the right proximal tibia by pQCT. BV/TV% of the left proximal tibia was measured by histo morphometry. Differences between groups were detected by all three met hods, but both the magnitude of the difference between groups and the variance of the measurements was much greater for histomorphometry and pQCT than for DXA. Consequently, the statistical significance for the difference between groups was comparable for all three methods. Of th e sites measured with DXA, the proximal tibia had the greatest statist ical significance for the difference between groups. In summary, all t hree methods can demonstrate the effect of orchiectomy on trabecular b one. The large differences between groups seen by histomorphometry are also seen by pQCT but not by DXA. We conclude that trabecular bone de nsity by pQCT may be a reasonable surrogate for measurements by histom orphometry.