Pig interleukin 1 (catabolin) is a potent stimulator of bone resorption in vitro

A homogeneous form of pig interleukin 1 (catabolin) stimulates the resorption of mouse bones in culture. Concentrations as low as 25 pM are effective, demonstrating that it is more potent than 1,25-dihydroxy-vitamin D3 in our assay system. Catabolin was originally defined by its ability to stimulate glycosaminoglycan release from cartilage in culture and purified from pig mononuclear leucocyte supernatants. It also augments lectin-induced thymocyte proliferation, indicating that it is a form of pig interleukin 1. Bone resorbing factors are synthesized by other cell types, including fibroblasts and osteoblasts; we suggest that such cytokines are important in mediating the action of systemic hormones on bone.