Inhibition via opioid mu- and delta-receptors of vagal transmission in rabbit isolated heart.
The nervi vagi of isolated perfused rabbit hearts were stimulated by 10 s trains of electrical pulses at 1, 2 or 5 Hz. Morphine, Met-enkephalin and D-Ala2,D-Leu5-enkephalin reduced the ensuing bradycardia with IC50 values of 148, 25 and 3.2 nM, respectively. Naloxone antagonized the effects of morphine and Met-enkephalin; KB values (dissociation constants of antagonist-receptor complex) were 1.1 and 33 nM, respectively. The delta-receptor-selective antagonist ICI 174864 antagonized Met-enkephalin, KB 28 nM, but at 0.2 microM did not antagonize morphine. It is concluded that vagal transmission to the rabbit heart can be inhibited by activation of both opioid mu- und delta-receptors.
D000109:Acetylcholine / Q000494:pharmacology; D000818:Animals; D004558:Electric Stimulation; D004743:Enkephalin, Leucine / Q000031:analogs & derivatives / Q000494:pharmacology; D016308:Enkephalin, Leucine-2-Alanine; D004744:Enkephalin, Methionine / Q000494:pharmacology; D006321:Heart / Q000294:innervation*; D066298:In Vitro Techniques; D008297:Male; D009020:Morphine / Q000494:pharmacology; D009270:Naloxone / Q000494:pharmacology; D010275:Parasympathetic Nervous System / Q000187:drug effects; D011817:Rabbits; D011957:Receptors, Opioid / Q000378:metabolism*; D017465:Receptors, Opioid, delta; D017450:Receptors, Opioid, mu; D009435:Synaptic Transmission / Q000187:drug effects*; D014630:Vagus Nerve / Q000502:physiology*
D011957:Receptors, Opioid; D017465:Receptors, Opioid, delta; D017450:Receptors, Opioid, mu; D009270:Naloxone; D004744:Enkephalin, Methionine; D004743:Enkephalin, Leucine; D016308:Enkephalin, Leucine-2-Alanine; D009020:Morphine; C040643:N,N-diallyl-tyrosyl-alpha-aminoisobutyric acid-phenylalanyl-leucine; D000109:Acetylcholine