Evidence for a single opioid receptor type on the field stimulated rat vas deferens

Abstract A series of opioids have been used to study the heterogeneity of the opioid receptor system in rat vas deferentia. β-Endorphin, etorphune, etonitazine, D-Ala 2 -Nle 5 (des-COOH) enkephalin and, sufentanil behave as full agonists in this tissue preparation. Ketobemidone, α(+)-N-allyl normetazocine, morphine and oxymorphone show little or no biological activity. In fact, the latter four drugs were able to inhibit the biological effects of β-endorphin, etorphine and sufentanil in a concentration dependent fashion. These data suggest that there is only one opioid receptor type in the rat vas deferens. These observations are discussed in terms of the binding modes for a series of drugs to an homogeneous receptor system.