Bone resorption by isolated chick osteoclasts in culture is stimulated by murine spleen cell supernatant fluids (Osteoclast‐Activating Factor) and inhibited by calcitonin and prostaglandin E₂

The question of whether any of the agents known to activate bone resorption in vivo or in organ cultures acts directly on the osteoclast or via intermediate target cells that secondarily secrete locally paracrine factors is important for our understanding of bone remodeling. In an attempt to clarify this issue for some of the agents, we have taken advantage of the recent progress in obtaining and culturing relatively pure populations of...