AGE-DEPENDENCE AND MODULATION BY GONADECTOMY OF THE SEX-SPECIFIC RESPONSE OF RAT DIAPHYSEAL BONE TO GONADAL-STEROIDS

We have previously reported that diaphyseal bone of prepubertal rats r esponds in a sex-specific manner to gonadal steroids, 24 h after stero id injection, by increases in creatine kinase (CK) specific activity a nd the rate of DNA synthesis. We have also shown that hormonal interve ntion abolished the sex-specific response of diaphyseal bone to sex st eroids. In the present study, we examined the responsiveness of diaphy seal bone and cartilage to gonadal steroids in male and female Wister- derived rats at ages between 5 days and 1 yr. In both diaphyseal bone and cartilage of untreated control rats, a peripubertal peak of CK spe cific activity was seen, which was more pronounced in females. Diaphys eal bone, unlike epiphyseal cartilage, responded specifically to a sin gle injection of 17 beta-estradiol (E(2); 5 mu g/rat) in females and t o 5 alpha-dihydrotestosterone (DHT; 50 mu g/rat) in males. The highest response occurred peripubertally, but was skewed toward prepubertal a ges in males and postpubertal ages in females. To study the effect of gonadectomy on this sex-specific response of diaphyseal bone, rats wer e gonadectomized at the age of 24 or 180 days and from 4 days to 4 wee ks thereafter were challenged with either E(2) or DHT. Diaphyseal bone s of gonadectomized rats of either sex responded to both Ep and DHT, b eginning 7 days after surgery. Thus, in gonadectomized rats, there was a loss of the sex specificity of response to steroid hormones, which could be restored by replenishment, by five daily injections, of the c haracteristic hormone of each sex. In the epiphyseal cartilage, the sa me replenishment schedule resulted in acquisition of a sex-specific re sponse in both sexes, not seen previously. These data in conjunction w ith the previously reported hormonal modulation of sex-specific respon ses, are consistent with a developmental acquisition of diaphyseal sex steroid specificity that requires for its maintenance the presence of appropriate amounts of the characteristic gonadal steroid in each sex .