The Journal of pharmacology and experimental therapeutics
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J. Pharmacol. Exp. Ther. · May 2000
Protein kinase C-mediated acute tolerance to peripheral mu-opioid analgesia in the bradykinin-nociception test in mice.
We studied the acute tolerance liability of peripheral opioid analgesia in mice. The analgesia was assessed by the inhibition of bradykinin (BK)-induced nociceptive action by using a newly developed flexor reflex paradigm. Morphine [intraplantarly (i.pl.)] given ipsilaterally to BK showed a dose-dependent reduction of the BK (2 pmol) responses, whereas the administration of 10 nmol of morphine into the contralateral side failed to show any significant analgesic effects. ⋯ Although morphine analgesia by the second challenge was markedly attenuated, U-69593 analgesia was not. The attenuated morphine analgesia was completely reversed by the pretreatment of calphostin C, Go6976, or HBDDE, a protein kinase C inhibitor, but not by KT-5720, a protein kinase A inhibitor. These results suggest that selective acute tolerance of peripheral morphine analgesia, but not U-69593 analgesia, through MORs and KORs located on polymodal nociceptors, respectively, in the bradykinin-nociception test in mice was mediated through protein kinase C activation.