title: Effects of yohimbine on morphine analgesia and physical dependence in the rat.
abstract: The effects of yohimbine on morphine analgesia and on the development of opiate physical dependence were studied to find out more about the involvement of alpha 2-adrenergic mechanisms in opioid actions. Male Sprague-Dawley rats (250-300 g) were used. The acute effect of morphine (5 mg/kg i.p.) in the tail-flick test was reduced significantly by pretreatment with a single dose of yohimbine (2 mg/kg i.p.). Alone yohimbine, produced a slight hyperalgesia. Animals treated with a sustained-release preparation of morphine (300 mg/kg s.c.) showed the same sensitivity to opiate analgesia 72 h later whether they were treated concomitantly with yohimbine or not, but they exhibited fewer withdrawal symptoms upon naloxone injection after yohimbine (2 or 4 mg/kg i.p. 24, 28, 48 and 52 h after the start of systemic morphine treatment). The results obtained confirm previous data on the effects of yohimbine on morphine analgesia and reveal the importance of alpha 2-adrenergic activation in the development of opioid physical dependence.
authors.affiliation: Department of Physiology and Pharmacology, University of Alcalá de Henares, Madrid, Spain.
authors.forename: V
authors.initials: V
authors.lastname: Iglesias
authors.forename: L F
authors.initials: LF
authors.lastname: Alguacil
authors.forename: C
authors.initials: C
authors.lastname: Alamo
authors.forename: E
authors.initials: E
authors.lastname: Cuenca
mesh_terms: D000698:Analgesia; D000818:Animals; D001522:Behavior, Animal / Q000187:drug effects; D003692:Delayed-Action Preparations; D008297:Male; D009020:Morphine / Q000008:administration & dosage / Q000494:pharmacology*; D009021:Morphine Dependence / Q000503:physiopathology*; D009270:Naloxone / Q000008:administration & dosage; D051381:Rats; D011919:Rats, Inbred Strains; D015016:Yohimbine / Q000008:administration & dosage / Q000494:pharmacology*
chemical_list: D003692:Delayed-Action Preparations; D015016:Yohimbine; D009270:Naloxone; D009020:Morphine