28. Effects of Orchidectomy on Bone Metabolism in Beagle Dogs

Satoshi Fukuda and Haruzo iida

Keywords: canine, bone histomorphometry, iliac bone, orchidectomy

The effects of orchidectomy on bone metabolism in male beagle dogs were examined using twelve 2 year-old dogs that were orchidectomized. The bilat eral iliac bones, double-labeled with tetracycline and calcein for the histomorphometry, were obtained from three dogs prior to orchidectomy and at 3, 6, 9 and 12 months afterwards. The serum biochemical constituents related to bone metabolism were exam ined before and every month after orchidectomy Between 1 and 6 months after orchidectomy, the value of serum testosterone decreased (1 month) while the levels of parathyroid hormone, calcitonin, total calcium, osteocalcin, and alkaline phosphatase activity increased significantly, indicating a high bone turnover. The mean trabecular thickness and the fraction of labeled osteoid surface decreased sig nificantly 3 months after orchidectomy, but other histomorphometric parameters were unchanged. In the period 7-12 months after orchidectomy, the parathyroid hormone level increased above that of the first 6-month period, while the levels of calcitonin, osteocalcin, alkaline phosphatase activity, and phosphorus decreased. The bone volume, mean trabecular thickness, and the fraction of labeled trabecular surface decreased significantly compared with the pre-orchidectomy values. These findings indicate an imbalance in bone metaboltsm (i.e. bone resorption > bone formation). These resuits indicate that a loss of bone volume accompanied the fall in sex hormone levels following orchidectomy and suggest that the orchidectomized dog is available as an animal model for studying osteoporosis caused by hypogonadism and the decline of sex functions in male humans.

Fig.12. Decrease in bone (BV/TV) after orchidectomy, shown as percentages of the value before orchidectomy, shown as percentages of the values before orchidectomy in each group. There was a significant decrease in bone volume (p<0.05) at 12 months compared to the value before orchidectomy.

Publicatuon:
Fukuda, S., and Iida, H.: Jpn.Vet. Sci., 62, 69-73, 2000.