Potent antinociceptive effects of TRK-820, a novel kappa-opioid receptor agonist

Life Sci. 1999;65(16):1685-94. doi: 10.1016/s0024-3205(99)00417-8.


TRK-820, a new type of 4,5-epoxymorphinan derivative, was investigated in vivo for antinociceptive activities and its selectivity on various opioid receptors in mice. TRK-820 given s.c. or p.o. was found to be 351- and 796-fold more potent than U50,488H with acetic acid-induced abdominal constriction test. The duration of the antinociceptive effect produced by TRK-820 was longer than that produced by mu-opioid receptor agonist morphine or other kappa-opioid receptor agonists. In addition, with four other antinociceptive assays, low temperature hot plate (51 degrees C), thermal tail flick, mechanical tail pressure and tail pinch tests, TRK-820 was also found to be 68- to 328-fold more potent than U-50488H, and 41- to 349-fold more potent than morphine in producing antinociception, as comparing the weight of the different compound. However, TRK-820 was less active in inhibiting the high temperature (55 degrees C) hot plate response. The antinociceptive effects produced by TRK-820 were inhibited by nor-BNI, but not by naloxone or naltrindole (NTI) with the abdominal constriction test, indicating that the antinociception is selectively mediated by the stimulation of kappa-, but not mu- or delta-opioid receptors. Co-administration of TRK-820 with morphine slightly enhanced the antinociception induced by morphine in the mouse hot plate test. On the other hand, pentazocine significantly reduced the morphine-induced antinociception. TRK-820 produced sedation at doses, which are much higher than the doses for producing antinociception. These results indicate that the potent antinociception induced by TRK-820 is mediated via the stimulation of kappa-, but not mu- or delta-opiod receptors.

MeSH terms

  • Administration, Oral
  • Analgesics, Non-Narcotic / pharmacology
  • Analgesics, Opioid / administration & dosage
  • Analgesics, Opioid / pharmacology*
  • Animals
  • Constriction, Pathologic / chemically induced
  • Drug Interactions
  • Hypnotics and Sedatives / pharmacology
  • Injections, Subcutaneous
  • Male
  • Mice
  • Morphinans / administration & dosage
  • Morphinans / pharmacology*
  • Motor Activity / drug effects
  • Nociceptors / drug effects*
  • Pentazocine / pharmacology
  • Receptors, Opioid, kappa / agonists*
  • Receptors, Opioid, kappa / antagonists & inhibitors
  • Spiro Compounds / administration & dosage
  • Spiro Compounds / pharmacology*


  • Analgesics, Non-Narcotic
  • Analgesics, Opioid
  • Hypnotics and Sedatives
  • Morphinans
  • Receptors, Opioid, kappa
  • Spiro Compounds
  • TRK 820
  • Pentazocine