Osteoblastic Insufficiency Is Responsible for Maintenance of Osteopenia after Loss of Ovarian Function in Experimental Beagle Dogs*

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Abstract
Bone loss developing after cessation of ovarian function in humans represents a major health problem. To establish the value of ovariohysterectomy in female beagle dogs as a model for bone loss and to study static and dynamic parameters of bone associated with the negative bone balance occurring after cessation of ovarian function, we performed iliac crest bone biopsies before and 4 months after ovariohysterectomy in eight beagle dogs and in five sham-operated controls. Cessation of ovarian function was documented by an increase in serum levels of LH 4 weeks after ovariohysterectomy. There was no change in serum calcium, phosphorus, and creatinine during the 4 months of the study. Cancellous bone mass and trabecular mean wall thickness decreased significantly after ovariohysterectomy (P < 0.01). In addition, the number of osteoblasts was increased and the bone formation rate per osteoblast, that is, the activity of bone-forming cells, was decreased (P < 0.01). Parameters of bone resorption were not significantly altered in the animals with ovariohysterectomy. No changes in histomorphometric parameters of bone structure, formation or resorption were observed in the sham-operated controls. These data indicate that ovariohysterectomy in beagle dogs may serve as a useful model for bone loss associated with cessation of ovarian function. Osteoblastic insufficiency appears to play a major role in the maintenance of bone loss ocurring after ovariohysterectomy in beagle dogs.