The effect of cyclosporin A administration on bone metabolism in the rat evaluated by biochemical markers.

We investigated the effects of cyclosporin A (CsA), an immunosuppressive agent, on bone remodeling in 6 rats compared to 6 controls, using a histomorphometric technique and biochemical markers for bone metabolism. With an oral daily dose of 15 mg CsA/kg of body weight for 28 days, the trabecular bone volume in CsA administered rats was significantly lower than that in control rats, which indicates bone loss in CsA rats. In CsA rats, bone resorption increased, and urinary pyridinoline (Pyr) significantly increased on day 28 compared with control rats. In contrast, bone formation assessed by serum osteocalcin and osteoid volume had no remarkable changes. These results suggest that administration of CsA for 28 days induces bone loss due to uncoupling between bone resorption and bone formation.