Development of tolerance to effects of morphine on cardiac sympathetic response.
1. In isolated guinea-pig atria, morphine potentiated the response to sympathetic stimulation in a naloxone-insensitive, but calcium-sensitive way. The potentiating effect of morphine disappeared in the presence of desmethylimipramine; moreover morphine enhanced the dose-effect curve for exogenous noradrenaline. 2. Morphine was ineffective in guinea-pig atria obtained from animals implanted with morphine pellets for 4 days; on the other hand DADLE and dynorphin-(1-13) maintained their usual inhibitory effect on cardiac sympathetic response in the same kind of preparation. 3. In atria obtained from morphine-tolerant animals and maintained in vitro in the presence of morphine, removal of morphine from the bathing solution caused a new potentiating effect.
Mantelli
L
L
Department of Pharmacology, University of Florence, Italy.
Corti
V
V
Ledda
F
F
D000818:Animals; D004361:Drug Tolerance; D004558:Electric Stimulation; D006168:Guinea Pigs; D006321:Heart / Q000294:innervation* / Q000502:physiology; D066298:In Vitro Techniques; D009020:Morphine / Q000494:pharmacology*; D009200:Myocardial Contraction / Q000187:drug effects; D009294:Narcotics / Q000494:pharmacology; D009638:Norepinephrine / Q000494:pharmacology; D013375:Substance Withdrawal Syndrome / Q000503:physiopathology; D013564:Sympathetic Nervous System / Q000187:drug effects*
D009294:Narcotics; D009020:Morphine; D009638:Norepinephrine