title: Possible presynaptic inhibitory effect of etorphine on sympathetic nerve terminals of guinea-pig heart.
abstract: Etorphine (1-4 microM) dose dependently reduced the sympathetic response induced by trains of field pulses in guinea-pig isolated atria stimulated at 4 Hz; this effect was antagonized by 10 microM naloxone. Since etorphine did not modify the dose-inotropic effect curve of exogenous noradrenaline in the same preparation, it is suggested that the depressant effect of the opioid agonist was due to stimulation of presynaptic inhibitory opiate receptors on adrenergic nerve terminals of the heart.
mesh_terms: D000818:Animals; D004305:Dose-Response Relationship, Drug; D005048:Etorphine / Q000494:pharmacology*; D006168:Guinea Pigs; D006321:Heart / Q000294:innervation*; D066298:In Vitro Techniques; D009019:Morphinans / Q000494:pharmacology*; D009020:Morphine / Q000494:pharmacology; D009200:Myocardial Contraction / Q000187:drug effects; D011957:Receptors, Opioid / Q000187:drug effects; D013564:Sympathetic Nervous System / Q000187:drug effects*
chemical_list: D009019:Morphinans; D011957:Receptors, Opioid; D005048:Etorphine; D009020:Morphine