Time-related increase of biochemical markers of bone turnover in androgen-deficient male rats.

Bone loss during androgen deficiency has been associated with accelerated bone turnover and imbalance between bone formation and resorption but the relative increase of both phenomena is not well described. Serum osteocalcin as marker of bone formation and urinary excretion of pyridinoline (PYD) and deoxypyridinoline (DPD) as markers of bone resorption were measured in both orchidectomized (ORCH, n = 8) and sham-operated (SHAM, n = 8) aged (12-month-old) male rats from 2 days before until 66 days after surgery. PYD and DPD were significantly higher in the ORCH group compared to the SHAM group starting from 21 days after surgery until the end of the experiment. Serum osteocalcin was only significantly increased in the ORCH group at 30 and 40 days. The maximal increase of serum osteocalcin was also smaller than the increase in PYD and DPD (30% versus 74% and 112%, respectively). The two markers of bone resorption were correlated with osteocalcin (r = 0.63 for PYD and r = 0.71 for DPD). Based on these results, we conclude that (1) bone resorption, as measured by PYD and DPD, increased during androgen deficiency; (2) moreover, the increase of bone resorption, as measured by DPD and PYD, was followed by a more moderate increase in bone formation as measured by serum osteocalcin, supporting the hypothesis that androgen deficiency causes accelerated bone turnover and imbalance between bone resorption and bone formation.