Effect of ovariectomy and prednisolone on bone mineral content in rats: evaluation by single photon absorptiometry and radiogrammetry.

The effects of ovariectomy and prednisolone were studied for 9 months in 3-month-old rats on a moderately low calcium diet. Measurements were made by single photon absorptiometry of the femur at cortical and trabecular bone sites. Radiogrammetry was performed at the midshaft of the femur. During growth, body weight, bone size, and bone mineral content (BMC) increased in male rats more than in females. After ovariectomy, body weight increase was more pronounced, but bone mineral increase was lower than in controls. At the distal end of the femur, bone mineral density decreased after 3 months, and at the midshaft of the femur, medullary width increased significantly from 6 months on. Prednisolone in a dose of 0.5 mg/kg/day did not influence BMC. However, prednisolone treatment after ovariectomy induced a more pronounced effect on bone than ovariectomy alone. BMC increase was lower than in ovariectomy, and bone mineral density decreased significantly, especially at the distal end of the femur. After correction for differences in body weight, globally the same results were found. We conclude that (1) the combination of single photon absorptiometry and radiogrammetry allows the evaluation of growth and the effect of ovariectomy and prednisolone treatment in rats; (2) ovariectomy results in bone loss first at the distal end and later in the midshaft of the femur; (3) prednisolone in a dose of 0.5 mg/kg/day alone did not affect bone mass; and (4) prednisolone profoundly enhanced the effects of ovariectomy.