Effects of chronic morphine treatment on catecholamines content and mechanical response in the rat hearts.
Our investigation was aimed at elucidating if the chronic administration and withdrawal of a preferential mu-agonist, morphine, induce changes on the heart catecholaminergic neuronal activity. With this purpose the effects of morphine or naloxone (preferentially mu-antagonist) on noradrenaline, adrenaline or dopamine (DA) content and the mechanical response of the left atria were studied in chronically placebo- or morphine-treated rats (implanted s.c. with pellets for 7 days). In morphine-treated rats, a challenge dose of morphine (30 mg/kg i.p.) increased the auricular noradrenaline, adrenaline and DA content and decreased dihydroxy phenyl acetic acid/DA ratio; these changes were accompanied by a decrease in the force of contraction in the isolated left atria. No changes were observed in placebo-treated rats. The administration of naloxone (1 mg/kg s.c.) to morphine-treated animals induced a decrease on the auricular content of noradrenaline, adrenaline and DA and an increase in dihydroxy phenyl acetic acid/DA ratio. The study of the mechanical response to naloxone in the isolated left atria showed an enhancement in the force of contraction in preparations from morphine-treated rats, whereas in the placebo-pelleted rats naloxone induced a decrease in this parameter. These findings demonstrate that the heart of rats that had received chronic morphine-treatment exhibit excitatory reactions to naloxone-precipitated withdrawal and suggest that the changes observed in the heart by the chronic administration of morphine and after naloxone precipitated withdrawal are mostly mediated by the catecholaminergic system.
Rabadán
J V
JV
Department of Physiology and Pharmacology, University School of Medicine, Murcia, Spain.
Milanés
M V
MV
Laorden
M L
ML
D000701:Analgesics, Opioid / Q000494:pharmacology*; D000818:Animals; D002395:Catecholamines / Q000032:analysis*; D006321:Heart / Q000187:drug effects*; D008297:Male; D009020:Morphine / Q000494:pharmacology*; D009206:Myocardium / Q000737:chemistry; D009270:Naloxone / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley
D000701:Analgesics, Opioid; D002395:Catecholamines; D009270:Naloxone; D009020:Morphine