[Age-related changes and sex differences in bone resorption in the mouse femur: a light and scanning electron microscopic study].

Bone resorption surfaces can be identified as rough areas by scanning electron microscopy. In this study, for understanding the principle of bone resorption and influences of gonads on the bone resorption in long bones, osteoclasts and bone resorption surfaces in the femur were qualitatively and quantitatively examined by light and scanning electron microscopy in 250 dd-mice of both sexes at 4, 7, and 14 weeks of age; some of the animals were gonadectomized at 4 weeks and examined at 7 and 14 weeks. The numbers of osteoclasts and bone resorption surfaces on the distal trabecular bones in the femur were large at 4 and 7 weeks and became smaller at 14 weeks. The area-proportion of the bone resorption surfaces in the distal trabecular bone region was large at 4 weeks and decreased with age. The number of osteoclasts and the number and area-proportion of the bone resorption surfaces were greater in females than males at 7 and 14 weeks. The sex-differences after puberty were large at 14 weeks than 7 weeks. After gonadectomy, the above values were not changed in females but significantly increased in males. In gonadectomized mice, the values were greater in males than females at 14 weeks. The results suggest that bone resorption activities change corresponding to the growth rate of the femur and receive inhibitory influences by male gonadal products, possibly androgenic hormones.