Platelet factor 4 regulates osteoclastic bone resorption in vitro.

Platelet factor 4, which inhibits collagenases derived from both human skin and granulocytic extracts, was found to block reversibly parathyroid hormone-stimulated 45Ca release from fetal rat bone in vitro. The inhibitory property was equally effective in both actively resorbing bones and in bones stimulated to initiate resorption.