Author(s): Litvinova SV, Kozlov AIu, Kaliuzhny LV
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Abstract In morphine-sensitive (s.c. 1.5 mg/kg) Wistar rats (60\%) i.p. inoculation of 300-600 mg/kg d-Phenylalanine (d-Pha) did not change the nociception (tail-flick test), but in morphine-resistant rats (40\%) evoked a dose-dependent analgetic effect. In morphine-sensitive rats (40\%) chronic morphine administration induced the tolerance and d-Pha injection evoked analgetic effect. Morphine injection just after d-Pha analgesia was over evoked analgetic effect in morphine-resistant and -tolerant rats. It is suggested that morphine-resistant rats have a congenital and morphine-tolerant rats an acquired high level of enkephalinase activity which blocked the morphine analgetic action.
This article was published in Biull Eksp Biol Med
and referenced in Journal of Addiction Research & Therapy