Vitamin D3 metabolites and PTH synergistically stimulate bone formation of chick embryonic femur in vitro.

Bone remodelling depends on a balance formation and resorption. Little is known of the biological factors involved in bone formation, whereas there is much evidence that physiological factors, such as parathyroid hormone (PTH) and active metabolites of vitamin D3, influence resorption. Cells responsible for osteogenesis and and osteoclasis occur in close proximity, suggesting that both might be controlled by the same physiological factors in the micro-environment of the body fluid. To clarify the factors stimulating bone formation or accelerating osteogenic cell activity, we have examined the effects of vitamin D3 metabolites and PTH on bone formation in vitro. We report here that combinations of those metabolites especially 1 alpha,25-(OH)2D3 and 24R,25-(OH)2D3, directly stimulate calcification on bone synergistically with PTH.