DISTINCT EFFECTS OF OVARIAN TRANSPLANTATION AND EXOGENOUS 17-BETA-ESTRADIOL ON CANCELLOUS BONE OF OSTEOPENIC OVARIECTOMIZED RATS

Although 17 beta-oestradiol (E(2)) is known to prevent bone loss, prol onged administration of E, is unable to reverse this in female rats re ndered osteopenic by ovariectomy. To determine whether this reflects a failure to replace other components of ovarian function involved in b one metabolism, we compared the effects of administering E(2) to osteo penic ovariectomized (ovx) rats with those of ovarian transplantation. Ovariectomy was performed in female rats. After 13 weeks, by which ti me marked bone loss had occurred, one group of ovx animals received ov aries from donor rats, and, after a delay of 2 weeks to allow oestrus cycles to return, a further group received E(2) 5 mu g . kg(-1). day(- 1) for 9 weeks. The dose of E(2) was chosen as that which in prelimina ry studies restored mean serum E(2) levels to that of intact female ra ts. The study was terminated 24 weeks after ovariectomy. Both E(2) and ovarian transplantation largely restored indices of oestrogenic expos ure in ovx rats to those of sham-ovx animals. Animals receiving ovaria n transplants also showed a small increase in serum progesterone resto ration of serum testosterone. However, while ovarian transplantation a lso returned indices of cancellous bone metabolism to those of sham-ov x animals, there was little increase in bone volume. Interestingly, ex ogenous E(2) caused a greater increase in cancellous bone volume than ovarian transplantation but also caused more marked suppression of bon e formation, as assessed at the end of the study. In conclusion exogen ous E(2) and ovarian transplantation exerted distinct effects on skele tal metabolism in osteopenic ovx rats, although the basis for this dif ference is currently unclear.