Differences in periosteal and corticoendosteal bone envelope activities in spayed and intact beagles: a histomorphometric study.

Resorptive and formative characteristics of the periosteal and corticoendosteal envelopes of the ribs of intact and spayed Beagle dams were studied. Six 4-year-old Beagle dams were spayed at source and kept under observation for 12 months. Four intact age- and weight-matched Beagle dams were used as controls. Before euthanizing, all dams received tetracycline labeling of their bones. Histomorphometric analyses of resorptive and formative parameters of the periosteal and corticoendosteal envelopes were carried out blind. The results indicated that following oophorectomy, there is an increase in resorptive surfaces on the periosteum and corticoendosteum, and a decline of formative activity on these same envelopes. These changes were manifested to a greater extent on the corticoendosteum. The lack of ovarian hormones contributes to an increase in the mineralization lag-time on the periosteum. Although in both control and spayed dams a similar pattern of surface activity was observed on both envelopes investigated, the differences in degree may be attributable to the ovarian hormone withdrawal.