Changes of the Met-enkephalin-like peptide content induced by noxious stimuli in the rat incisor pulp

It was examined what mechanism involved in an increase of met-enkephalin (met-EK)-like peptide content in the pulp induced by noxious stimuli. The increased content of the peptides by cavity formation as noxious stimulation was not influenced by cycloheximide, but attenuated by FOY-305 [N,N-dimethyl carbamoyl-methyl 4-(4-guanidinobenzoyloxy) phenyl acetate methanesulfonate], a trypsin-like enzyme inhibitor, and enhanced by captopril, and attenuated by infusion of saline in the pulp cavity. From these results, it was suggested that noxious stimuli on the pulp led to activation of trypsin-like enzymes followed by an increased content of met-EK-like peptides, and thereafter, the peptides, such as met-EK, might be degraded by angiotensin converting enzyme (ACE). Furthermore, an immunohistochemical study demonstrated that met-EK-like immunoreactivity (met-EK-IR) of cells in the rat incisor pulp was clearly increased following tryptic digestion of the pulp section, supporting a suggestion mentioned above.