CHARACTERIZATION OF THE OPIOID RECEPTOR SUBTYPES MEDIATING THE NEGATIVE INOTROPIC EFFECTS OF DAMGO, DPDPE AND U-50,488H IN ISOLATED HUMAN RIGHT ATRIA STRIPS

The present investigation was aimed at elucidating if mu, delta- and k appa-opioid receptors are involved in the effects of DAMGO (selective mu-agonist), DPDPE (selective delta-agonist) and U-50,488H (selective kappa-agonist) in isolated electrically driven human right atria strip s. The negative inotropic effects induced by the opioid agonists used in this study were not antagonized in presence of naloxone (preferenti ally mu-antagonist), naltrindole (selective delta-antagonist) and nor- binaltorphimine (selective kappa-antagonist). These data suggest that the opioid receptors are not involved in the cardiac depressant effect s induced by mu-, delta- and kappa-opioid agonists.