Dose-response effects of estradiol implants on bone mineral density in ovariectomized ewes

In a longitudinal in vivo study, we studied the effect of two different doses of 17 beta-estradiol (E2) administered in the form of a subcutaneous implant, on bone mineral density (BMD) of the lumbar vertebrae (L4, L5, L4-L6/L5-L7), the calcaneus (CAL) and the distal radius (DR) in ovariectomized (OVX) ewes. The BMD of various regions of the femur, tibia and humerus were studied at autopsy. Skeletally mature ewes (n = 45) were divided into four groups: sham operated (n = 12), OVX (n = 15), OVX plus one E2 implant (OVXE, n = 12) and OVX plus two E2 implants (OVX2E, n = 6). BMD of L4, L5, L4-L6/L5-L7, CAL and DR was determined at 0, 6 and 12 months using dual-energy X-ray absorptiometry. In-vivo precision of BMD for the last three lumbar vertebrae ranged from 1.4-4.3%, and 1.5% and 3.5% for CAL and DR respectively. In the in vivo study, there were no significant changes in the mean BMD in the sham group at any time point (each group served as its own control). In the OVX group, mean BMD was significantly lower at L5 and DR at 6 months and significantly lower at L4 at 12 months. In the OVXE group, the mean BMD was significantly higher at L5, CAL and DR at 12 months. In the OVX2E group, BMD was significantly higher at CAL but significantly lower at L4 at 12 months. None of the treatments produced significant changes of mean BMD of L4-L6/L5-L7 at any time point.(ABSTRACT TRUNCATED AT 250 WORDS)