Relationship between serum estradiol, cathepsin K, and N-telopeptide of type I collagen in female dogs.

Ovariohysterectomized (OHE) female dogs do not develop the osteopenia and osteoporosis associated with decreasing estrogen in post-menopausal women, possibly due to post-OHE bone mineral density retention through a mechanism that remains unclear. In this study, we aimed to elucidate this mechanism by investigating estradiol (E2) and bone markers. Samples were collected from 56 OHE and 43 intact bitches (0.33 to 17.58 years old) and analyzed for serum E2, osteoclast-secreted cysteine protease cathepsin K (CTK), and N-telopeptide of type I collagen (NTx) by ELISA. OHE and intact bitches showed no significant difference in serum E2 or NTx, and there was no correlation between serum E2 and NTx and age and time since OHE. Intact bitches showed a very low correlation between E2 and NTx, but OHE bitches showed no correlation, and serum CTK was generally undetectable in both groups. Our findings suggest the influence of gonadal hormones on bone metabolism does not work effectively in dogs; this is consistent with a shorter duration of exposure to E2 in bitches (through the 4-to-8-month anestrus phase) than women.