The effect of bradykinin and desArg'-bradykinin on bone was studied in cultures of calvarial bones taken from 6-7-day-old mice. Bradykinin, at and above a 3-nM concentration, caused a dose-dependent stimulation of bone mineral mobilization and matrix degradation. Bradykinin-stimulated resorption was inhibited by calcitonin, an increased concentration of phosphate in the culture medium, hydrocortisone, dexamethasone, indomethacin, meclofenamic acid, naproxen, and 5,8,11,14-eicosatetraenoic acid. The results suggest that bradykinin stimulates osteoclast-mediated bone resorption by a process that is dependent on endogenous prostaglandin production. The stimulatory effect of bradykinin, but not of parathyroid hormone and prostaglandin E2, was potentiated by the angiotensinconverting enzyme inhibitor, BPPs,. Treatment with carboxypeptidase B did not affect the capacity of the peptide to stimulate 45Ca release. DesArg'-bradykinin (1 pnole/liter) stimulated 45Ca release to the same degree as did bradykinin. Bradykinin (3 pM) did not affect the degradation of cartilage proteoglycans, as assessed by the release of 35S-sulfate from prelabeled calf articular cartilage in organ culture. These findings suggest that generation of bradykinin in inflammatory lesions of rheumatoid arthritis and periodontitis may -____ contribute to the bone resorptive process seen in the joints and alveolar bone; however, bradykinin does not directly activate chondrocytes into a catabolic state.Destruction of soft tissues and mineralized tissues is a characteristic finding in rheumatoid arthritis (RA) and periodontitis, the most common chronic inflammatory processes. The inflammatory lesions of RA and periodontal disease are composed of different cell types that are capable of producing degradative enzymes. These enzymes can be released extracellularly and, thereby, contribute to the breakdown of surrounding cartilage and fibrous tissues. Bone destruction is a consequence of the interaction of inflammatory cells and multinuclear osteoclasts, the cells responsible for the breakdown of bones. Potential mediators involved in the communication between inflammatory mononuclear cells and osteoclasts include osteoclast-activating factor, which is synthesized by stimulated lymphocytes (for review, see ref. l), prostaglandin E2 (PGE2) (for review, see ref.2), and nonprostanoid products released by monocytes (3,4), especially interleukin-I (5,6). To this list, we have recently added thrombin (7), a serine esterase that is generated during the coagulation cascade.Bradykinin is a small vasoactive peptide that is formed by the cleavage of high molecular weight kininogen by kallikrein (for review, see ref. 8). It is known primarily for its effects on vascular tone and permeability (for review, see ref. 8). In areas of inflammation, bradykinin may be formed in parallel with the generation of thrombin, since prekallikrein is activated to kallikrein by coagulation factor XIIa (Hageman factor) (9,lO). This fact has prompted our study of the possible role of the k...