Teruo Kudo

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 involvement of the central endorphin system in the autoanalgesia induced by chronic administration of freund's adjuvant solution in rats

Abstract Chronic pain was induced in rats by daily injections of complete Freunds adjuvant into hind paws. Daily changes of pain threshold and endorphin (ED) content and their receptors in 4 divided parts: cortex, diencephalon‐mesencephalon containing striatum (D‐M), pons‐medulla (P‐M) and spinal cord, were measured. Decrease in pain responsiveness was observed in the adjuvant‐injected group with concomitant increase of ED content in P‐M and spinal cord. This decrease in pain responsiveness in the adjuvant‐injected group was significantly different from that in the non‐treated control group being partially reversed by naloxone. Furthermore, [3H]met‐enkephalin binding sites increase in number in P‐M of the adjuvant‐injected group when maximal decrease of pain responsiveness was observed, returning to control level thereafter. Scatchard analysis revealed the increase of the low affinity binding site in P‐M of the adjuvant‐injected group. In cortex and D‐M, on the other hand, ED content tended to decrease and no change was observed in number of [3H]met‐enkephalin binding sites. These results indicate that the ED system in P‐M and spinal cord may be more substantially involved in autoanalgesia than in cortex and D‐M.

OPIOID PEPTIDE IN THE DOG CANINE PULP

Pharmacological and histological studies on existence of opioid peptides in the dog canine pulp were performed. Content of opioid peptides in the pulp was determined by radioimmunoassay, using methionine-enkephalin(ME) antiserum. ME-like substance could be detected, the contents ranging from 38.5 to 1269.7 p mol /g wet weight of the pulp. On the other hand, immunohistochemical studies of the dog canine pulp were performed by the indirect immunofluorescence method. Diffusely throughout the pulp tissues except for around the blood vessels, many ME-like immunoreactive(MELI) cells containing the fluorescent granules were observed, while the fluorescence disappeared when the control serum was used. Anatomical and physiological significances of the ME positive cells detected in the pulp still remain to be elucidated.

Bradykinin as an algesic (pain producing) substance in the pulp.

SummaryA rat uterine smooth muscle contracting substance was released into the superfusate of the dogs exposed canine pulp after noxious stimulation of the pulp by pricking, heat and electrical stimulation. This active substance was acid- and heat-resistant and was decomposed by carboxypeptidase B and α-chymotrypsin, but not by carboxypeptidase A and trypsin. This substance was also tested on several types of smooth muscle. Electrical activity of nerve cells in the reticular formation, which were sensitive to stimulation of the instep of the foot by pinching, was activated by the intrafemoral administration of the active substance. The algesic activity of this substance was examined in cantharidin blister base in man. This study conclusively demonstrated that the active substance of the pulp released by noxious stimulation produced pain and it was identified as bradykinin.

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.

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.

Enkephalins and bradykinin in dental pulp

Abstract The physiological significance of enkephalins in the periphery remains obscure. Reizo Inoki and Teruo Kudo review the evidence for a possible role for enkephalin in the dental pulp. The content of enkephalins in the dental pulp is increased by noxious stimuli (e.g. cavity formation) through the activation of trypsin-like enzymes which produce opioid peptides from precursor proteins. Bradykinin may be a trigger in this regard. The authors propose that enkephalins may play an autoregulatory role regarding noxious reactions.

In vitro production and release of opioid peptides in the tooth pulp induced by bradykinin

A possible relationship between met-enkephalin (ME)-like peptides and bradykinin (BK) in the rat incisor pulp was examined in in vitro experiments using whole pulp. ME-like peptide content in the pulp was increased by BK at a concentration of 1 microM, but not in higher concentrations, while the release of ME-like peptides from the pulp into the incubation medium was increased dose-dependently by BK. These effects of BK were inhibited by Des-Arg9-[Leu8]-BK, a potent BK-antagonist, suggesting that the effects of BK were mediated through a specific BK-receptor in the pulp. On the other hand, high K+ did not induce any increased release of ME-like peptides from the pulp and the BK effects were influenced neither in Ca++-free medium nor in the presence of ouabain. These results suggested that ME-like peptide releasing effect of BK was not due to depolarization of the cell membrane and was not active. In addition, kyotorphin, and enkephalin-releaser, could not only elicit a release of ME-like peptides from the pulp, but also a marked increase of the peptide content in the pulp. However, a combination of BK and kyotorphin attenuated the effect of BK or kyotorphin each other. These results suggested that there might be two kinds of mechanisms of ME-like peptide production in the pulp and those mechanisms might interfere mutually.

Effects of aspirin and morphine on the release of a bradykinin-like substance into the subcutaneous perfusate of the rat paw

&NA; The effects of aspirin and morphine on the release of a bradykinin‐like substance into the subcutaneous perfusate following various noxious stimuli were investigated in the rat paw preparation. Subcutaneous perfusion was performed with saline or with saline containing o‐phenathroline or soy bean trypsin inhibitor at a rate of 3–4 drops/min. Ten drops per fraction were assayed for bradykinin activity. Pressure on the instep, application of heat to the foot and stimulation of the sciatic nerve were employed as noxious stimuli. Aspirin (200 mg/kg i.p.) inhibited the release of bradykinin due to heat, pressure and sciatic nerve stimulation, while morphine (5 mg/kg i.m.) inhibited only the release of bradykinin due to sciatic nerve stimulation. Results suggest that analgesics, such as aspirin and morphine, have a depressant action on pain by inhibiting the release of bradykinin locally. They also suggest that aspirin inhibits the release of bradykinin regardless of the type of noxious stimuli, while morphine inhibits the release of bradykinin which is mediated by neural mechanisms.

Nechanism of Substance P-Induced Salivary Secretion in Rats

Leeman and Hammerschlag (1,2) found a potent sialogogic substance in the rough extract from bovine or rat hypothalamus. This sialogogue has been known to be substance P itself. Although substance P (SP), one of tachykinins, has been recognized as a neurotransmitter (3,4) or a modulator (5,6) of the primary sensory neurone, mechanism of sialogogic action of this substance still remained undissolved.