Anorectic activity of fluoxetine and norfluoxetine in rats: Relationship between brain concentrations and in-vitro potencies on monoaminergic mechanisms

S. Caccia, A. Bizzi, G. Coltro, C. Fracasso, E. Frittoli, T. Mennini, S. Garattini

Research output: Contribution to journalArticlepeer-review

Abstract

The present study was aimed at establishing the importance of brain monoamine uptake and release mechanisms in the anorectic activity of fluoxetine, relating them to the actual brain concentrations of the parent drug and its metabolite norfluoxetine after anorectic doses in rats. Both compounds showed anorectic activity when administered intraperitoneally norfluoxetine being slightly more active (ED50=22.9μmol kg-1) than fluoxetine (ED50=35.0μmol kg-1) despite the fact that the metabolite is about ten times less potent than the parent drug in inhibiting 5-hydroxytryptamine (5-HT) uptake. Comparing the brain concentrations of norfluoxetine in terms of maximum concentrations (C(max)) and area under the curve (AUC) after the ED50 of fluoxetine or synthetic norfluoxetine it also appeared that the metabolite plays a major role in the anorectic effect of the parent drug in rats. Brain C(max) of fluoxetine (48.7μM) and norfluoxetine (21.7 and 27.3μM after metabolite and drug respectively) were several times those blocking 5-HT uptake in-vitro (0.5μM), making it unlikely that fluoxetine (directly or through its metabolite) reduces food intake by specifically blocking 5-HT neuronal uptake. Brain C(max) of of fluoxetine but particularly norfluoxetine were more compatible with those capable in-vitro of affecting catecholaminergic mechanisms such as inhibition of dopamine and noradrenaline uptake and enhancement of dopamine release. These results together with recent in-vitro findings that the parent compound and its active metabolite induce tritium release from hippocampal synaptosomes previously loaded with [3H]5-HT suggest that mechanisms other than inhibition of 5-HT uptake are involved in the anorectic action of these compounds in rats.

Original languageEnglish
Pages (from-to)250-254
Number of pages5
JournalJournal of Pharmacy and Pharmacology
Volume44
Issue number3
Publication statusPublished - 1992

ASJC Scopus subject areas

  • Pharmaceutical Science
  • Pharmacology

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