title: Pretreatment with protein kinase C activator phorbol 12,13-dibutyrate attenuates the antinociception induced by mu- but not epsilon-opioid receptor agonist in the mouse.
abstract: The effects of pretreatment with a protein kinase C activator, phorbol 12,13-dibutyrate, on antinociception induced by i.c.v.-administered mu-opioid receptor agonist (D-Ala2, NMePhe4, Gly(ol)5) enkephalin (DAMGO) or morphine and epsilon-opioid receptor agonist beta-endorphin were studied in male ICR mice. The tail-flick responses were used for antinociceptive tests. I.c.v. pretreatment with phorbol 12,13-dibutyrate (50 pmol) for 30 or 60 but not 10 min attenuated antinociception induced by i.c.v.-administered DAMGO. I.c.v. pretreatment with phorbol 12,13-dibutyrate (10 and 50 pmol) for 60 min caused a dose-dependent attenuation of DAMGO (19.5 pmol)- or morphine (6.0 nmol)-induced antinociception. The dose-response curve for DAMGO-induced antinociception was shifted to the right by 7.3-fold by i.c.v. pretreatment with phorbol 12,13-dibutyrate (50 pmol) for 60 min. However, the i.c.v.-administered beta-endorphin-induced antinociception was not affected by the same pretreatment with phorbol 12,13-dibutyrate. The attenuation of i.c.v.-administered DAMGO- and morphine-induced antinociception by phorbol 12,13-dibutyrate was reversed by concomitant i.c.v. pretreatment with a selective protein kinase C inhibitor calphostin C. These results suggest that activation of protein kinase C by phorbol 12,13-dibutyrate leads to the desensitization of mu-, but not epsilon-opioid receptor-mediated antinociception. These findings also provide additional evidence for differential intracellular modulation on antinociceptive action of mu- and epsilon-opioid receptor agonists.
authors.affiliation: Department of Anesthesiology, Medical College of Wisconsin, Milwaukee 53226, USA.
authors.forename: M
authors.initials: M
authors.lastname: Narita
authors.forename: M
authors.initials: M
authors.lastname: Ohsawa
authors.forename: H
authors.initials: H
authors.lastname: Mizoguchi
authors.forename: J
authors.initials: J
authors.lastname: Kamei
authors.forename: L F
authors.initials: LF
authors.lastname: Tseng
mesh_terms: D000700:Analgesics / Q000494:pharmacology; D000818:Animals; D004305:Dose-Response Relationship, Drug; D020875:Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; D004745:Enkephalins / Q000494:pharmacology; D004789:Enzyme Activation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D007276:Injections, Intraventricular; D008297:Male; D051379:Mice; D008813:Mice, Inbred ICR; D009281:Naphthalenes / Q000494:pharmacology; D009619:Nociceptors / Q000187:drug effects*; D010147:Pain Measurement; D015240:Phorbol 12,13-Dibutyrate / Q000494:pharmacology*; D011493:Protein Kinase C / Q000378:metabolism*; D011957:Receptors, Opioid / Q000819:agonists*; D017450:Receptors, Opioid, mu / Q000819:agonists*; D013997:Time Factors; D001615:beta-Endorphin / Q000494:pharmacology
chemical_list: D000700:Analgesics; D004745:Enkephalins; D004791:Enzyme Inhibitors; D009281:Naphthalenes; D011957:Receptors, Opioid; D017450:Receptors, Opioid, mu; C043460:epsilon receptor; D020875:Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; D015240:Phorbol 12,13-Dibutyrate; D001615:beta-Endorphin; D011493:Protein Kinase C; C058819:calphostin C