Differential role of the opioid mu and delta receptors in the activation of prolactin (PRL) and growth hormone (GH) secretion by morphine in the male rat

Administration of naloxazone (50 mg/kg i.v.), an irreversible, selective and long acting antagonist of the mu 1 subclass of the opioid receptors, strongly reduced stimulation of PRL secretion by morphine (5.0 mg/kg i.v.) injected 24 hours later into conscious, unrestrained rats. In contrast, the eff...

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Bibliographic Details
Published inLife sciences (1973) Vol. 34; no. 19; p. 1829
Main Authors Koenig, J I, Mayfield, M A, McCann, S M, Krulich, L
Format Journal Article
LanguageEnglish
Published Netherlands 07.05.1984
Subjects
Animals
Drug Interactions
Enkephalin, Leucine - analogs & derivatives
Enkephalin, Leucine - pharmacology
Growth Hormone - metabolism
Injections, Intraventricular
Male
Morphine - pharmacology
Naloxone - analogs & derivatives
Naloxone - pharmacology
Naltrexone - analogs & derivatives
Naltrexone - pharmacology
Prolactin - metabolism
Rats
Rats, Inbred Strains
Receptors, Opioid - metabolism
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Summary:Administration of naloxazone (50 mg/kg i.v.), an irreversible, selective and long acting antagonist of the mu 1 subclass of the opioid receptors, strongly reduced stimulation of PRL secretion by morphine (5.0 mg/kg i.v.) injected 24 hours later into conscious, unrestrained rats. In contrast, the effect of morphine on PRL release was unimpaired in rats treated 24 hours beforehand with either the reversible opioid antagonist naloxone (50 mg/kg i.v.), or the vehicle for naloxazone. A complete suppression of the PRL response to morphine (3.0 mg/kg i.v.) was observed in animals given intraventricular (IVT) injection of beta- funaltrexamine (beta-FNA, 2.5 micrograms), another selective, irreversible and long acting antagonist of the mu receptors, 24 hours beforehand. Neither naloxazone nor beta-FNA had any effect on the activation of GH secretion by morphine, which, however, was conspicuously reduced by ICI 154, 129, a preferential delta receptor antagonist, injected IVT (50 micrograms) 5 minutes before morphine. ICI 154, 129 had no effect on the PRL response to morphine. It is concluded that the PRL stimulating effect of morphine is mediated by the mu receptors, whereas activation of GH probably involves the delta sites.
ISSN:0024-3205
DOI:10.1016/0024-3205(84)90676-3