Antinociceptive effect produced by intracerebroventricularly administered dynorphin A is potentiated by p-hydroxymercuribenzoate or phosphoramidon in the mouse formalin test.
The antinociceptive effects of intracerebroventricularly (i.c.v.) administered dynorphin A, an endogenous agonist for kappa-opioid receptors, in combination with various protease inhibitors were examined using the mouse formalin test in order to clarify the nature of the proteases involved in the degradation of dynorphin A in the mouse brain. When administered i.c.v. 15 min before the injection of 2% formalin solution into the dorsal surface of a hindpaw, 1-4 nmol dynorphin A produced a dose-dependent reduction of the nociceptive behavioral response consisting of licking and biting of the injected paw during both the first (0-5 min) and second (10-30 min) phases. When co-administered with p-hydroxymercuribenzoate (PHMB), a cysteine protease inhibitor, dynorphin A at the subthreshold dose of 0.5 nmol significantly produced an antinociceptive effect during the second phase. This effect was significantly antagonized by nor-binaltorphimine, a selective kappa-opioid receptor antagonist, but not by naltrindole, a selective delta-opioid receptor antagonist. At the same dose of 0.5 nmol, dynorphin A in combination with phosphoramidon, an endopeptidase 24.11 inhibitor, produced a significant antinociceptive effect during both phases. The antinociceptive effect was significantly antagonized by naltrindole, but not by nor-binaltorphimine. Phenylmethanesulfonyl fluoride (PMSF), a serine protease inhibitor, bestatin, a general aminopeptidase inhibitor, and captopril, an angiotensin-converting enzyme inhibitor, were all inactive. The degradation of dynorphin A by mouse brain extracts in vitro was significantly inhibited only by the cysteine protease inhibitors PHMB and N-ethylmaleimide, but not by PMSF, phosphoramidon, bestatin or captopril. The present results indicate that cysteine proteases as well as endopeptidase 24.11 are involved in two steps in the degradation of dynorphin A in the mouse brain, and that phosphoramidon inhibits the degradation of intermediary delta-opioid receptor active fragments enkephalins which are formed from dynorphin A.
Tan-No
K
K
Department of Pharmacology, Tohoku Pharmaceutical University, 4-4-1 Komatsushima, Aoba-ku, 981-8558, Sendai, Japan. koichi@tohoku-pharm.ac.jp
Ohshima
K
K
Taira
A
A
Inoue
M
M
Niijima
F
F
Nakagawasai
O
O
Tadano
T
T
Nylander
I
I
Silberring
J
J
Terenius
L
L
Kisara
K
K
D000818:Animals; D001921:Brain / Q000187:drug effects* / Q000378:metabolism; D002457:Cell Extracts / Q000494:pharmacology; D004347:Drug Interactions / Q000502:physiology*; D004399:Dynorphins / Q000378:metabolism / Q000494:pharmacology*; D006020:Glycopeptides / Q000494:pharmacology*; D006902:Hydroxymercuribenzoates / Q000494:pharmacology*; D007276:Injections, Intraventricular; D051379:Mice; D009271:Naltrexone / Q000031:analogs & derivatives* / Q000494:pharmacology; D009292:Narcotic Antagonists / Q000494:pharmacology; D009619:Nociceptors / Q000187:drug effects* / Q000378:metabolism; D010146:Pain / Q000188:drug therapy* / Q000503:physiopathology; D010147:Pain Measurement / Q000187:drug effects; D011480:Protease Inhibitors / Q000494:pharmacology*; D051381:Rats
D002457:Cell Extracts; D006020:Glycopeptides; D006902:Hydroxymercuribenzoates; D009292:Narcotic Antagonists; D011480:Protease Inhibitors; C030601:4-hydroxymercuribenzoate; C051844:norbinaltorphimine; D009271:Naltrexone; D004399:Dynorphins; C055382:naltrindole; C008890:phosphoramidon