Interaction between bradykinin and enkephalins in rat dental pulp

The content of bradykinin (BK)-like peptides in rat dental pulp was significantly increased 1, 6 and 24 h after cavity formation at the neck of incisor. We have reported that enkephalin (EK)-like peptides in rat dental pulp were increased by cavity formation or BK. In the present study, the mechanism of the production of EK enhanced by BK was investigated using benzoyl-L-arginine-2-naphthylamide (BANA), a synthetic substrate. BK and its products cleft by carboxypeptidase B, des-Arg9-BK and arginine (Arg), activated the degradation of BANA. It is suggested that these substances may enhance the processing of enkephalins from precursor proteins. The activating effects were inhibited by EGTA. The BANA-degrading enzymes in lysosomal fraction were activated by BK, des-Arg9-BK and Arg, but the enzymes in supernatant were activated by Arg only. On the other hand, morphine and met-EK inhibited the production of BK-like peptides by trypsin from plasma kininogen. It is suggested that BK is cleft by carboxypeptidase B in pulp cell to des-Arg9-BK and Arg, which activate the lysosomal or soluble EK processing enzymes, and then the produced EK inhibits the production of BK from plasma kininogens in the pulp.