Relative efficacies of 6-opioid receptor agonists at the cloned human δ-opioid receptor

The present study was conducted to determine the relative efficacies of the selective δ-opioid receptor agonists SNC80((+)-4-[(αR)-α-((2S,5R)-4-allyl-2,5-dimethyl-1- piperazinyl)-3- S,5 R) -4-allyl-2,5-dimethyl-1-piherazinyl)-3-methoxybenzyl]-N,N- diethylbenzamide), pCl-DPDPE (cyclic[D-Pen²,4'-ClPhe⁴,D-Pen⁵]enkephalin) and (-)-TAN67 ((-)-2-methyl-4aα-(3-hydroxyphenyl)-1,2,3,4,4a,5,12,12aα-octahyhro-quinolino -[2,3,3-g]isoquinoline). Experiments compared the abilities of the three drugs to competitively inhibit [³H]naltrindole binding and also stimulate [³⁵S]GTPγS binding in membranes prepared from stably transfected Chinese hamster ovary (CHO) cells that express the cloned human δ-opioid receptor. Efficacy was determined according to the formula: efficacy = (E(max-A)/E(maxi))(A'/A+1)x 0.5. Results show that SNC80 and pCl-DPDPE had efficacy values that were about 6-7 times greater than that of(-)-TAN67.