Table 1. Affinities of Leu-Enkephalin and Compounds 1–8 on DOPr^a.

^aThe binding affinity (K_i) of each compound was determined by its ability to inhibit the binding of [³H]-deltorphin II (competitive binding), a selective DOPr agonist, to GH3/DOPr cell membrane extracts. K_i values are the means ± SEM of three separate experiments each performed in triplicate.