Hyperglycaemia: a morphine-like effect produced by naloxone.
1. Naloxone, which is often regarded as a pure opioid antagonist, produces effects similar to those produced by morphine. 2. In conscious rabbits implanted with an intracerebroventricular (i.c.v.) cannula, naloxone, whether given intravenously (1 mg/kg) or i.c.v. (1-100 microg), produced a significant rise in blood glucose levels. 3. Hyperglycaemia in response to naloxone (1 mg/kg, i.v., or 100 microg, i.c.v.) was not influenced by the selective alpha1-adrenoceptor antagonist WB-4101 given either i.v. (50 microg) or i.c.v. (5 microg). 4. Hyperglycaemia in response to naloxone (1 mg/kg, i.v., or 100 microg, i.c.v.) was completely blocked by pretreatment with the alpha2-adrenoceptor antagonist yohimbine (1 mg/kg, i.v., or 100 microg, i.c.v.). However, hyperglycaemia to i.c.v. naloxone (100 microg) was not influenced by i.v. yohimbine (1 mg/kg). 5. Because naloxone behaves like morphine and produces hyperglycaemia in conscious rabbits, the drug may have an appreciable agonist activity and the hyperglycaemic response to naloxone is principally mediated via alpha2- but not alpha1-adrenoceptors.
Abouazra
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Department of Pharmacology, Faculty of Medicine, Al-Arab Medical University, Benghazi, Libya. ABOUAZRA@yahoo.com
Sharif
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D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology; D000818:Animals; D001786:Blood Glucose / Q000187:drug effects* / Q000378:metabolism; D004146:Dioxanes / Q000494:pharmacology*; D006943:Hyperglycemia / Q000097:blood / Q000139:chemically induced*; D008297:Male; D009020:Morphine / Q000494:pharmacology*; D009270:Naloxone / Q000494:pharmacology*; D009292:Narcotic Antagonists / Q000494:pharmacology*; D009294:Narcotics / Q000494:pharmacology*; D011817:Rabbits; D018341:Receptors, Adrenergic, alpha-2 / Q000187:drug effects / Q000502:physiology; D015016:Yohimbine / Q000494:pharmacology
D000317:Adrenergic alpha-Antagonists; D001786:Blood Glucose; D004146:Dioxanes; D009292:Narcotic Antagonists; D009294:Narcotics; D018341:Receptors, Adrenergic, alpha-2; D015016:Yohimbine; D009270:Naloxone; D009020:Morphine; C010654:(2-(2',6'-dimethoxy)phenoxyethylamino)methylbenzo-1,4-dioxane