SPECIFIC BETA-ESTRADIOL BINDING IN CARTILAGE AND SERUM FROM YOUNG MICE AND RATS IS AGE-DEPENDENT

Various studies have shown a direct effect of beta estradiol on cartilage and bone. Such effects point to the possibility that specific receptors to estradiol exist in the growth plate cartilage as well as in bone. H-3-estradiol specific binding (EB) was therefore investigated in the supernatant of cartilage homogenates from the epiphyses and ribs of young growing mice and rats. High levels of EB were observed in the cytosol fraction of cartilage homogenates in the late fetal stage and in young rats and mice. The EB levels decreased gradually from late fetal stage up to 14 days of age in both groups of animals independent of their sex. Nuclear binding of 3H estradiol was also demonstrated by autoradiography in the chondrocytes of proliferating and hypertrophic zones. Estradiol binding was inhibited by high doses of unlabelled beta-estradiol, but not by alpha estradiol. Binding was also inhibited by tamoxifen and DES but not by testosterone. High levels of estradiol binding (EBS) were also observed in serum from young animals, but not in animals 2 months of age or older. Study of estradiol binding in cartilage and in serum of rats of the same age showed a significant difference in estradiol binding between these two systems. The difference in estradiol binding between serum and cartilage was seen in the response to inhibitors, Scatchard analysis, and temperature dependence. The results of our study imply that there are specific receptors for 17beta estradiol in growth plate cartilage; they originate from chondrocytes, and their amount decreases with age. The effects of estradiol on endochondral bone growth seems therefore to be receptor mediated.