EFFECT OF 17-BETA-ESTRADIOL ON THE HEALING OF TIBIAL BONE AFTER MARROW ABLATION

The present study has been undertaken to demonstrate the effect of 17 beta-estradiol on the healing of tibial bones after marrow ablation. N inety-six 4-month-old female rats were divided into three experimental groups: group I was subjected to ablation in both tibiae and to injec tion of vehicle; group 2 to ablation in both tibiae and estradiol admi nistration, and group 3 to estradiol administration without ablation. Before the rats were killed, all on the same day, 8 animals of each gr oup underwent treatment for 3, 6, 14 and 21 days, respectively: every second day, 0.1 ml arachis oil was injected intramuscularly into group 1 and 17 beta-estradiol into groups 2 and 3. An additional 8 untreate d animals were used as controls. Tibial bones were studied chemically and morphologically. While the control and ablated animals gained weig ht, there was a significant decrease in the gain in body weight of est radiol-treated rats. Bone and ash weight were increased in all experim ental groups. The ratios (%) of tibial ash weight and of tibial Ca and Mg contents to body weight significantly increased in all experimenta l groups, compared to the controls; whereas P increased only at 6 and 14 days. As shown by computerized histomorphometry, the height of the proximal tibial growth plate was increased following ablation, but not with estradiol treatment. The proportions by area of calcified cartil age and metaphyseal trabeclar bone were significantly lower and the pe rcentage of bone marrow was higher in al groups treated for 3 and 6 da ys; the values were similar to those of the controls with 21 days of t reatment. The results of this study indicate that intramuscular admini stration of estradiol to adult rats, after marrow ablation, did not si gnificantly influence bone healing, as observed following ablation alo ne. It seems that the effects of estradiol on the bone of adult rats w ith slowly remodelling bones does not change with the increase in bone turnover, and that estradiol has little effect on endosteal bone unde rgoing enhanced remodelling.