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Distinct effects of ovarian transplantation and exogenous 17 β-oestradiol on cancellous bone of osteopenic ovariectomized rats

Gallagher AC, Chambers TJ, Tobias JH. Distinct effects of ovarian transplantation and exogenous 17 β-oestradiol on cancellous bone of osteopenic ovariectomized rats. Eur J Endocrinol 1995;133:483–8. ISSN 0804–4643

Although 17 β-oestradiol (E₂) is known to prevent bone loss, prolonged administration of E₂ is unable to reverse this in female rats rendered osteopenic by ovariectomy. To determine whether this reflects a failure to replace other components of ovarian function involved in bone metabolism, we compared the effects of administering E₂ to osteopenic ovariectomized (ovx) rats with those of ovarian transplantation. Ovariectomy was performed in female rats. After 13 weeks, by which time marked bone loss had occurred, one group of ovx animals received ovaries from donor rats, and, after a delay of 2 weeks to allow oestrus cycles to return, a further group received E₂ 5 µg · kg^–1 · day^–1 for 9 weeks. The dose of E₂ was chosen as that which in preliminary studies restored mean serum E₂ levels to that of intact female rats. The study was terminated 24 weeks after ovariectomy. Both E₂ and ovarian transplantation largely restored indices of oestrogenic exposure in ovx rats to those of sham-ovx animals. Animals receiving ovarian transplants also showed a small increase in serum progesterone and full restoration of serum testosterone. However, while ovarian transplantation also returned indices of cancellous bone metabolism to those of sham-ovx animals, there was little increase in bone volume. Interestingly, exogenous E₂ caused a greater increase in cancellous bone volume than ovarian transplantation but also caused more marked suppression of bone formation, as assessed at the end of the study. In conclusion, exogenous E₂ and ovarian transplantation exerted distinct effects on skeletal metabolism in osteopenic ovx rats, although the basis for this difference is currently unclear.

JH Tobias, Department of Histopathology, St George's Hospital Medical School, London SW17 ORE, UK