Bradykinin stimulates production of prostaglandin E 2 and prostacyclin in murine osteoblasts

Abstract

The effect of bradykinin on prostaglandin production in mouse calvarial bones and in isolated osteoblasts has been examined. Bradykinin (1 μmol/l) stimulated prostaglandin formation in neonatal mouse calvarial bones incubated for 30 min. In isolated osteoblast-like cells from neonatal mice calvarial bones and in a cloned mouse calvarial osteoblastic cell lineage (MC3T3-E1) bradykinin stimulated the production of prostaglandin E 2 (PGE 2) and 6-keto-prostaglandin F 1α (the stable breakdown product of prostacyclin). The stimulation of PGE 2 production occurred rapidly (30 s) and reached its maximum after 5–10 min. The stimulatory effect of bradykinin on PGE 2 production in isolated osteoblast-like cells and in MC3T3-E1 cells was dose dependent with apparent half maximal stimulation seen at 10 and 3 nmol/l, respectively. Bradykinin-induced prostaglandin production was totally reversible after withdrawal of the agonist. Pretreatment with bradykinin (1 μmol/l) resulted in desensitization to a subsequent challenge with bradykinin (1 μmol/l), while pretreatment with bradykinin had no effect upon arachidonic acid (30 μmol/l) induced prostaglandin formation. Bradykinin-induced production of PGE 2 was abolished by several structurally unrelated, competitive and non-competitive inhibitors of arachidonic acid metabolism as well as by corticosteroids. The mouse calvarial osteoblast-like cells also showed a PGE 2 and 6-keto-PGF 1α response to thrombin, but not to parathyroid hormone (PTH), calcitonin and 1α(OH)D 3. The formation of cyclic AMP in mouse calvarial osteoblasts was enhanced by PTH, bradykinin, thrombin and arachidonic acid but not by calcitonin and 1α(OH)D 3. The cyclic AMP response to bradykinin, thrombin and arachidonic acid, but not that to PTH, was abolished by indomethacin. The degree of confluency of the cell cultures greatly influenced the amount of prostaglandins being produced. At higher cell density the amount of prostanoids synthesized per cell was substantially decreased in untreated control cultures as well as in bradykinin- and arachidonic acid-treated cells. These data suggest that osteoblasts are equipped with receptors for bradykinin coupled to prostaglandin production.