Enhancement of opiate-induced depressions in serum luteinizing hormone levels by the prior administration of maloxone in the male rat

Theodore J. Cicero, Dennis P. Owens, Peter F. Schmoeker, Edward R. Meyer

Research output: Contribution to journalArticle

6 Scopus citations

Abstract

The effects of naloxone pretreatment on opiate agonist-induced depressions in serum luteinizing hormone (LH) levels were examined in male rats. Our results demonstrated a pronounced enhancement of morphine's actions 6 hours after the administration of naloxone (0.5 mg/kg). This effect was characterized by a 10 fold reduction in the ED50 (1.26 mg/kg versus 0.13 mg/kg in saline- and naloxone-pretreated rats, respectively) and much greater depressions in serum LH levels at each dose of morphine. The actions of naloxone were not confined to morphine, since similar increased potencies were found for opioid agonists with selectivity for a variety of opioid receptor subtypes. Because naloxone did not alter the uptake of subsequently administered morphine into brain, our results cannot be explained on the basis of an increased availability of the agonist. Rather, it appears that naloxone pretreatment induces a change in the sensitivity of those receptors involved in the effects of opioid agonists on LH.

Original languageEnglish
Pages (from-to)1321-1328
Number of pages8
JournalLife Sciences
Volume35
Issue number12
DOIs
StatePublished - Sep 17 1984

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