Differential involvement of mu-opioid receptor subtypes in endomorphin-1- and -2-induced antinociception.


We investigated the role of mu-opioid receptor subtypes in both endomorphin-1 and endomorphin-2 induced antinociception in mice using supraspinally mediated behavior. With tail pressure as a mechanical noxious stimulus, both intracerebroventricularly (i.c.v.) and intrathecally (i.t.) injected-endomorphins produced potent and significant antinociceptive activity. Antinociception induced by i.t. and i.c.v. injection of endomorphin-1 was not reversed by pretreatment with a selective mu1-opioid receptor antagonist, naloxonazine (35 mg/kg, s.c.). By contrast, antinociception induced by i.t. and i.c.v. endomorphin-2 was significantly decreased by mu1-opioid receptor antagonist. Antinociception of both i.t. and i.c.v. endomorphin-1 and -2 was completely reversed by pretreatment with beta-funaltrexamine (40 mg/kg, s.c.). The results indicate that endomorphins may produce antinociception through the distinct mu1 and mu2 subtypes of mu-opioid receptor.

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@article{Sakurada1999DifferentialIO, title={Differential involvement of mu-opioid receptor subtypes in endomorphin-1- and -2-induced antinociception.}, author={Shinobu Sakurada and James E. Zadina and Abba J. Kastin and Soh Katsuyama and Takashi Fujimura and Kei Murayama and Miyata Yuki and Hiroshi Ueda and Tsukasa Sakurada}, journal={European journal of pharmacology}, year={1999}, volume={372 1}, pages={25-30} }