Influences of bradykinin and substance P on the met-enkephalin-like peptide content in the rat incisor pulp.

The present study was aimed to examine possible influences of bradykinin (BK) and substance P (SP) on met-enkephalin (ME)-like peptide content in the rat incisor pulp. Des-Arg9-[Leu8]-BK, a potent BK-antagonist, significantly reduced the increased content of ME-like peptides induced by noxious stimulation, while the effect of BK-antagonist was reversed in combination with BK. Morphine decreased the increased content of ME-like peptides. Ethylketocyclazocine, a kappa-agonist, also decreased the increased content of the peptides. From these results, it was suggested that BK might be a trigger in the increase of ME-like peptide content induced by noxious stimulation and, in contrast, ME-like peptides in the pulp might inhibit BK release from the pulp in a negative feedback mechanism. On the other hand, [D-Pro2,D-Trp7,9]-SP, a potent SP-antagonist, did not show any significant influence to ME-like peptide content in the pulp. Furthermore, the content was not changed following cutting of inferior alveolar nerve. From these results, it was suggested that ME-like peptides in the pulp cells might be independent on SP-containing nerves in the pulp.