DISCRIMINATION OF 3 OPIATE RECEPTOR-BINDING SITES WITH THE USE OF A COMPUTERIZED CURVE-FITTING TECHNIQUE

  • 1 January 1982
    • journal article
    • research article
    • Vol. 21  (2) , 266-271
Abstract
The presence of different types of opiate binding sites was investigated with the use of a computerized, weighted, nonlinear least-squares regression program. The experimental data were obtained from 4 groups. Each of 3 labeled opiate ligands was displaced using each of the same unlabeled ligands. The resulting 9 different ligand combinations of each group were evaluated by use of a curve-fitting program. The 4 groups consisted of the .kappa. ligand ethylketocyclazocine, the .sigma. ligand SKF 10047 [N-allylnormetazocine], and the oripavine derivatives etorphine and diprenorphine, each in conjunction with the .delta. opiate receptor ligand (D-Ala2,D-Leu5)-enkephalin and the .mu. opiate receptor ligand dihydromorphine. The binding model which best fitted each of the 4 groups suggested the existence of 3 different binding sites in the rat brain homogenate. Two of these sites conform to the previously described .mu. and .delta. sites. A 3rd site (R3) displayed high affinity for ethylketocyclazocine, SKK 10047 etorphine and diprenorphine but very low affinity for dihydromorphine and [D-Ala2,D-Leu5]enkephalin. Naloxone, cyclazocine and dynorphin-(1-13) had high affinity for R3. Behavioral data support the interpretation that the R3 site may represent a .kappa. site at which SKF 10047 acts antagonistically.

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