Bradykinin‐induced burst of prostaglandin formation in osteoblasts is mediated via B2 bradykinin receptors

The receptor subtype mediating the bradykinin (Bk)‐induced burst of prostaglandin formation in osteoblasts has been studied. Bk, but not des‐Arg9‐Bk, induced the formation of prostaglandin E2 and prostacyclin in neonatal mouse calvarial bones incubated for 30 minutes. Bk‐induced prostaglandin synthesis in neonatal mouse calvarial bones was significantly inhibited by the B2 Bk receptor antagonist D‐Arg0[Hyp3, Thi5,8, D‐Phe']‐Bk. The B2 Bk receptor agonists Bk and Lys‐Bk, but not the B1 Bk receptor agonist des‐Arg9‐Bk, caused a rapid burst (5 minutes) of prostaglandin E2 and prostacyclin formation in isolated osteoblast‐like cells from neonatal mouse calvarial bones and in the murine osteoblastic cell lineage MC3T3‐E1. When comparing the relative potency of different kinin analogs on their stimulatory effect on prostaglandin formation in isolated osteoblast‐like cells and in MC3T3‐E1 cells, we found that Bk = Lys‐Bk > Met‐lys‐Bk >>> Des‐Arg9‐Bk. Bk‐induced prostaglandin synthesis in isolated osteoblast‐like cells and in MC3T3‐E1 cells was inhibited by D‐Arg0[Hyp3, Thi5,8, D‐Phe7]‐Bk, whereas the B1 Bk receptor antagonist des‐Arg9‐Leu8‐Bk had no effect. Total binding of 3H‐Bk (3–20 nM; 4°C) to whole MC3T3‐E1 cells reached a maximum after 4–5 h. An excess of nonradioactive Bk (1 μM) reduced cell‐associated radioactivity by 20–30%. The B2 Bk receptor agonist Bk and the B2 Bk receptor antagonist D‐Arg0[Hyp3, Thi5,8, D‐Phe7]‐Bk were able to reduce specific binding, but the B1 Bk receptor agonist des‐Arg9‐Bk was unable to reduce the specific binding of 3H‐Bk to whole MC3T3‐E1 cells. These findings indicate the presence of B2 Bk receptors on osteoblasts coupled to enhanced prostaglandin synthesis.