title: Effect of three peptidase inhibitors on antinociceptive potential and toxicity with intracerebroventricular administration of dynorphin A (1-17) or (1-13) in the rat.
abstract: OBJECTIVE
  The N- and C-terminal regions of dynorphin (Dyn) A (1-17) activate opioid and N-methyl-D-aspartate receptors, respectively. Earlier studies demonstrated that Dyn-converting enzyme cleaved Dyn A (1-17) mainly at the Arg(6)-Arg(7) bond, resulting in the production of N- and C-terminal region peptide fragments, and that this enzyme was not inhibited by a mixture of the three peptidase inhibitors (PIs) amastatin (A), captopril (C), and phosphoramidon (P). The purpose of the present study was to evaluate antinociceptive potential and toxicity with intracerebroventricular administration of Dyn A (1-17) or (1-13) under pretreatment with a mixture of A, C, and P and/or Dyn-converting enzyme inhibitor (p-hydroxymercuribenzoate).
  
  
  METHODS
  Peptide fragments from Dyn A (1-17) following incubation with membrane preparation under pretreatment with a mixture of the three PIs was identified by matrix-assisted laser desorption ionization time-of-flight mass spectrometer (MALDI-TOF-MS). Infusion of drugs and peptides into the third ventricle in rats was performed via indwelling cannulae. Induction of antinociception and toxicity by Dyn A (1-17), Dyn A (1-13), Dyn A (1-6), or Dyn A (7-17) were determined by the tail-flick test and induction of barrel rotation, respectively. The effects of the PIs on antinociception and toxicity were evaluated by a dose-response study and a comparison of differences among various combinations of Dyn A (1-17) or Dyn A (1-13) and the three PIs and p-hydroxymercuribenzoate.
  
  
  RESULTS
  MALDI-TOF-MS analysis identified Dyn A (1-6) and Dyn A (1-10) fragments as products following incubation of Dyn A (1-17) with membrane preparation of rat midbrain under pretreatment with a mixture of the three PIs. Pretreatment with a mixture of the three PIs produced an approximately 30-fold augmentation in antinociception induced by low-dose intracerebroventricular administration of Dyn A (1-17) or (1-13) in a μ-, δ- and κ-opioid receptor antagonist-reversible manner, but without signs of toxicity such as barrel rotation in the rat. Dyn A (1-17)-induced antinociception and toxicity was greater than that of Dyn A (1-6), Dyn A (1-13), or Dyn A (7-17) at the same dose. Dyn A (1-17)-induced antinociception and toxicity under pretreatment with various combinations of the three PIs and p-hydroxymercuribenzoate was greater than that with a mixture of the three PIs alone.
  
  
  CONCLUSIONS
  These findings suggest that administration of a mixture of the three PIs increases Dyn A (1-17)- or (1-13)-induced antinociception under physiological conditions without toxicity.
authors.affiliation: Department of Anesthesiology, School of Medicine, Tokai University, Isehara, 259-1193, Japan.
authors.forename: Junko
authors.initials: J
authors.lastname: Ajimi
authors.forename: Masanobu
authors.initials: M
authors.lastname: Yoshikawa
authors.forename: Shigeru
authors.initials: S
authors.lastname: Takahashi
authors.forename: Masaaki
authors.initials: M
authors.lastname: Miura
authors.forename: Hideo
authors.initials: H
authors.lastname: Tsukamoto
authors.forename: Mitsuru
authors.initials: M
authors.lastname: Kawaguchi
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Kobayashi
authors.forename: Toshiyasu
authors.initials: T
authors.lastname: Suzuki
mesh_terms: D000700:Analgesics / Q000009:adverse effects* / Q000494:pharmacology*; D000701:Analgesics, Opioid / Q000008:administration & dosage / Q000494:pharmacology / Q000633:toxicity*; D000818:Animals; D001923:Brain Chemistry / Q000187:drug effects; D002216:Captopril / Q000008:administration & dosage / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004399:Dynorphins / Q000008:administration & dosage / Q000494:pharmacology / Q000633:toxicity*; D006020:Glycopeptides / Q000008:administration & dosage / Q000494:pharmacology; D007276:Injections, Intraventricular; D008297:Male; D010147:Pain Measurement / Q000187:drug effects; D010455:Peptides / Q000008:administration & dosage / Q000494:pharmacology; D011480:Protease Inhibitors / Q000494:pharmacology*; D051381:Rats; D017208:Rats, Wistar; D011957:Receptors, Opioid / Q000187:drug effects
chemical_list: D000700:Analgesics; D000701:Analgesics, Opioid; D006020:Glycopeptides; D010455:Peptides; D011480:Protease Inhibitors; D011957:Receptors, Opioid; C016977:amastatin; D004399:Dynorphins; D002216:Captopril; C008890:phosphoramidon