Influence of oestrogen and androgen on modelling of the mandibular condylar bone in ovariectomized and orchiectomized growing mice

Oestrogen and androgen exert a substantial influence on bone metabolism, but any differences in their influence on modelling of the condyle, a mandibular growth site, have not been fully clarified. The purpose here was to examine histological and histochemical differences in the condyle of ovariectomized (OVX) or orchiectomized (ORX) mice given injections of oestrogen (E2, 17β-oestradiol) or non-aromatizable androgen (DHT, 5α-dihydrotestosterone). Eight-week-old C57BL/6J mice (n=170) were used: they were divided equally into six experimental groups (OVX, ORX, OVX+E2, ORX+E2, OVX+DHT, ORX+DHT), and non-treatment male and female control groups. In each experimental group, five mice were killed 2, 4, 8 and 12 weeks after OVX and ORX. Oestrogen or androgen were given daily after the surgery by subcutaneous injection of E2 or DHT. Increases in the number of tartrate-resistant acid phosphatase-positive cells induced in the OVX and ORX mice from 4 to 12 weeks after surgery were obviously suppressed by E2 and DHT. The trabecular bone volume in the OVX and ORX mice treated with DHT had only increased at 12 weeks after surgery, whereas the E2 injected mice exhibited a substantial increase from 4 to 12 weeks after surgery. E2 injected into the OVX and ORX mice increased the trabecular bone volume earlier than did DHT, and both E2 and DHT suppressed osteoclast differentiation similarly during the same period. These results suggest that metabolic responses of osteoclasts and osteoblasts to E2 and DHT may be different, producing somewhat different patterns of bone modelling in males and females.