Yoshiyasu Uchida

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.

A possible relationship between processing from precursor proteins to opioid peptides and noxious stimulation in the rat incisor pulp

The content of met-enkephalin (met-EK)-like peptides in a crude extract from intact pulp of the rat markedly increased with tryptic digestion but not with carboxypeptidase B(CPase B) digestion, while the content of leu-enkephalin (leu-EK)-like peptides more markedly with CPase B- than with tryptic digestion. On the other hand, results by High Performance Liquid Chromatography (HPLC) showed that the contents of both met-EK-Arg-Phe and leu-EK in cavity formed pulp increased 6 times as much as those contents in intact pulp, while the met-EK content in cavity formed pulp increased 2 times as much as that in intact pulp. Furthermore, results by gel filtration of crude extract from intact pulp showed that one peak of met-EK-like immunoreactivity (met-EK-IR) appeared at position of approximately 30,000 of molecular weight and a broad peak of leu-EK-IR appeared at position of approximately 60,000 of molecular weight following tryptic digestion. From these results, it was suggested that noxious stimuli might cause activation of trypsin-like enzymes followed by processing from one precursor protein to met-EK-like peptides as well as from another to leu-EK-like peptides in the rat incisor pulps.

Antagonism by glibenclamide of the effect of morphine in hippocampal preparations

We previously showed that morphine lowered the affinity of Ca2+ antagonist binding and subsequently enhanced field potentials in hippocampal preparations. In the present study, the effect of various K+ channel antagonists on these actions of morphine was studied. Higher Kd value of [3H]nitrendipine binding was obtained for membranes prepared from slices treated with morphine. Concomitant treatment of slices with morphine and tetramethylammonium (TMA) or glibenclamide attenuated the effect of morphine. Apamin and mast cell-degranulating (MCD) peptide were without effect on morphine-induced change in [3H]nitrendipine binding. In those experiments, no change in concentration of binding sites was observed. Glibenclamide reduced the morphine enhancement of field potentials. These results suggested the regulation of Ca2+ channels by morphine through K+ channel opening.

Effect of morphine on aluminium fluoride and dibutyryl-cyclic AMP induced reduction of field potentials in hippocampal slices.

Effects of morphine and aluminum fluoride on field potentials evoked in hippocampal pyramidal cells were investigated revealing the physiological significance of adenylate cyclase in morphine action. Dibutyryl-cyclic AMP (db-cAMP) reduces the amplitude of potentials, while morphine enhances it. Morphine was without effects on db-cAMP induced reduction of potentials. Aluminum fluoride, known to activate GTP binding proteins, also reduced potentials and this was antagonized by morphine. Furthermore, N-[2-(methylamino)ethyl]-5-isoquinolinesulphonamide dihydrochloride (H-8), a protein kinase A inhibitor, enhanced potentials. When GABA synthesis was inhibited by 3-mercaptopropinoic acid, both morphine and db-cAMP was without effect. These results suggested the inhibition of adenylate cyclase by morphine which might be related with the reduction of GABA release in hippocampal slices.