Three groups (n = 15/group) of 6-, 12- and 30-month-old (mature, old and senescent animals, respectively) female Wistar rats on a diet (6 g/100 g BW/ day) containing 0.8%
calcium and 0.8% inorganic
phosphorus were studied. Within each group, 10 rats were ovariectomized surgically and 5 injected s.c. with
17 beta-estradiol (E rats, 10 micrograms/kg BW/48 h) and 5 with
solvent alone (OVX rats) from day 2 until day 60 after
ovariectomy. Five other rats were
sham-operated (SH rats) and received
solvent only. All rats were killed by
exsanguination 60 days after
ovariectomy. Neither
ovariectomy nor
estradiol treatment had a significant effect upon tibial mechanical properties in 6-, 12- and 30-month-old animals. Bone mineral density (BMD) and bone mineral content (BMC) of the distal femur and BMC of the whole femur were decreased by
ovariectomy in 6- and 12-month-old rats, but were not different in the SH and E groups. In senescent animals, in which the lowest BMD and BMC were measured,
estradiol treatment was more effective in increasing these parameters than in adult and old rats. Image analysis of the distal femoral diaphysis showed that
estradiol treatment prevented trabecular bone loss induced by senescence and/or
ovariectomy. In each group, urinary
deoxypyridinoline excretion and plasma
osteocalcin concentration were higher in the OVX animals than in the controls, consistent with increased bone turnover in the
estrogen-deficient state. Both biochemical turnover markers were reduced in the
estrogen-treated groups. These results indicate that
17 beta-estradiol is particularly effective at preventing high-turnover-induced
osteopenia in 30-month-old animals.