Congenital osteoclast deficiency in osteopetrotic (op/op) mice is improved by ovariectomy and orchiectomy

We examined the changes in the appearance of osteoclasts in the femora of ovariectomized (OVX) or orchiectomized (ORX) op/op mice. Osteoclasts on the trabecular bone surface of the OVX or ORX op/op mice significantly increased in number seven or eight times in comparison with sham-operated op/op mice. Furthermore, TRAP-positive cells increased about four times in 100-week-old females and males, compared with sham-operated groups. These results have indicated that a sex hormone reduction due to OVX or ORX induces prominent recruitment of osteoclasts in op/op mice.