Effects of opioid drugs on capsaicin-sensitive neurones in guinea-pig atria.
Transmural nerve stimulation of isolated guinea-pig atria in the presence of atropine induced a biphasic positive inotropic effect but only a slow increase in contractility (NANC response) in atria obtained from 6-hydroxy-dopamine-pretreated animals. The latter effect disappeared after exposure of the preparations to capsaicin. The effects of some opioid peptides were investigated on NANC responses. [D-Ala2,D-Leu5]enkephalin (DADLE) and [D-Ala2,N-Me-Phe4,Gly5-ol]enkephalin (DAGO, 0.1-10 microM) inhibited the cardiac response to transmural nerve stimulation in a dose-dependent and naloxone-sensitive manner. Dynorphin-(1-13) and morphine, at 10-fold higher concentrations (1-10 microM), reduced the response in a naloxone-sensitive manner. Naloxone alone however did not affect the response. Opioid peptides were not able to reduce the positive inotropic effect induced by calcitonin gene-related peptide (CGRP), or the increase in cardiac contractility produced by capsaicin. These results suggest that opioid receptors exert a modulatory role on peripheral terminals of capsaicin-sensitive sensory nerves.
Mantelli
L
L
Department of Pharmacology, University of Florence, Italy.
Amerini
S
S
Ledda
F
F
D000818:Animals; D002211:Capsaicin / Q000494:pharmacology*; D004558:Electric Stimulation; D020875:Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; D004743:Enkephalin, Leucine / Q000031:analogs & derivatives / Q000494:pharmacology; D016308:Enkephalin, Leucine-2-Alanine; D004745:Enkephalins / Q000494:pharmacology; D006168:Guinea Pigs; D006321:Heart / Q000294:innervation* / Q000502:physiology; D066298:In Vitro Techniques; D008297:Male; D009200:Myocardial Contraction / Q000187:drug effects; D009294:Narcotics / Q000494:pharmacology*; D009475:Neurons, Afferent / Q000187:drug effects*; D013563:Sympathectomy, Chemical
D004745:Enkephalins; D009294:Narcotics; D020875:Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; D004743:Enkephalin, Leucine; D016308:Enkephalin, Leucine-2-Alanine; D002211:Capsaicin