SPECIFICITY OF OPIOIDS TOWARDS THE MU-OPIATE, DELTA-OPIATE AND EPSILON-OPIATE RECEPTORS

The potency of a number of opioid agonists has been determined on three different bioassays, the isolated guinea-pig ileum (GPI), the mouse vas deferens (MVD) and the rat vas deferens (RVD). With the exception of β-endorphin, compounds with opioid activity on the GPI and the MVD exhibited considerably less or no activity on the RVD; the opiate receptor in this latter tissue being thus characterized as β-endorphin selective ('ε{lunate}-receptor'). A system of classification of opioids according to their relative affinities for particular opiate receptor types is given. © 1979.