25-hydroxyvitamin D: autoradiographic evidence of sites of action in epiphyseal cartilage and bone.

Tritiated 25-hydroxyvitamin D3 was administered to growing rats to morphologically documents its sites of action. Highly selective incorporation occurred in epiphyseal hypertrophic cells, epiphyseal matrix, osteoid, osteoblasts, and osteocytes of metaphyseal bone spicules. The labeled metabolite appeared in chondrocytic lacunar matrix coincident with hypertrophic cell death as evidenced by histological examination. The tritiated 25-hydroxyvitamin D3 became localized only in areas of active mineralization.