Evidence for multiple "Kappa" binding sites by use of opioid peptides in the guinea-pig lumbo-sacral spinal cord

Neuropeptides. 1982 Oct;3(1):53-64. doi: 10.1016/0143-4179(82)90065-8.


Binding properties of [3H]-etorphine and [3H]-ethylketocyclazocine have been studied in the lumbo-sacral spinal cord of guinea-pig which does not contain mu or delta binding sites. [3H]-etorphine binds to a single class of high affinity sites, whereas [3H]-ethylketocyclazocine interacts with a high and a low affinity component. Using a discriminative procedure, 5 microM (D-Ala2, D-Leu5) enkephalin (DAL), the high affinity component of [3H]-ethylketocyclazocine can be resolved in two classes of sites, (D-Ala2, D-Leu5) enkephalin sensitive sites (DALS sites) and (D-Ala2, D-Leu5) enkephalin insensitive sites (DALI sites). In these conditions, there is a total loss of [3H]-etorphine sites, whose binding capacity and properties strictly correspond to the DALS sites labelled by [3H]-ethylketocyclazocine. Pharmacological investigations indicate that DALI sites for which dynorphin (1 leads to 17) is the best ligand, can be related to kappa sites previously described in guinea-pig brain, whereas DALS sites for which (Arg6, Phe7) Met-enkephalin possesses a good affinity, closely correspond to benzomorphan sites recently characterized in rat brain and spinal cord. [3H]-ethylketocyclazocine interacts additionally with "non opiate" low affinity sites, for which only benzomorphan drugs exhibit a good affinity, whereas morphine, naloxone, phencyclidine or endogenous opioid peptides do not present any affinity for them. On the basis of these data, a new subdivision of "kappa" sites is discussed.

MeSH terms

  • Animals
  • Binding Sites
  • Cyclazocine / analogs & derivatives
  • Cyclazocine / metabolism
  • Dihydromorphine / metabolism
  • Endorphins / metabolism*
  • Enkephalin, Leucine / analogs & derivatives
  • Enkephalin, Leucine / metabolism
  • Enkephalin, Leucine-2-Alanine
  • Ethylketocyclazocine
  • Etorphine / metabolism
  • Guinea Pigs
  • Radioligand Assay
  • Receptors, Opioid / metabolism*
  • Receptors, Opioid, kappa
  • Spinal Cord / metabolism*


  • Endorphins
  • Receptors, Opioid
  • Receptors, Opioid, kappa
  • Etorphine
  • Ethylketocyclazocine
  • Enkephalin, Leucine
  • Enkephalin, Leucine-2-Alanine
  • Dihydromorphine
  • Cyclazocine