Direct action of 1,25-dihydroxyvitamin D on bone: VDRKO bone shows excessive bone formation in normal mineral condition.

In the present study, the direct role of Vitamin D in bone metabolism was investigated. Vitamin D has been suggested to be an important hormone for bone metabolism, but there has been little evidence that Vitamin D actively participates in this process. Here, we show the direct action of Vitamin D by transplanting the bone of the Vitamin D receptor null mutant mice (VDR-/-) to the wild-type mouse. This procedure allowed us to investigate the changes in the bone without VDR in the normal humoral environment. Unexpectedly, the volume and the density of the VDR-/- bone transplanted to the wild-type mouse were significantly increased compared with the control (wild-type bone transplanted to the wild-type mouse). We show that Vitamin D has key roles in bone metabolism negatively.