PT  - JOURNAL ARTICLE
AU  - Richard B. Rothman
AU  - Robert D. Clark
AU  - John S. Partilla
AU  - Michael H. Baumann
TI  - (+)-Fenfluramine and Its Major Metabolite, (+)-Norfenfluramine, Are Potent Substrates for Norepinephrine Transporters
AID  - 10.1124/jpet.103.049684
DP  - 2003 Jun 01
TA  - Journal of Pharmacology and Experimental Therapeutics
PG  - 1191--1199
VI  - 305
IP  - 3
4099  - http://jpet.aspetjournals.org/content/305/3/1191.short
4100  - http://jpet.aspetjournals.org/content/305/3/1191.full
SO  - J Pharmacol Exp Ther2003 Jun 01; 305
AB  - (±)-Fenfluramine is an amphetamine analog that was once widely prescribed as an appetite suppressant. Although (±)-fenfluramine is no longer clinically available, the mechanisms underlying its anorectic properties are still of interest. Upon peripheral administration, stereoisomers of (±)-fenfluramine are N-deethylated to form the metabolites, (+)- and (-)-norfenfluramine. It is well accepted that isomers of (±)-fenfluramine and (±)-norfenfluramine interact with 5-hydroxytryptamine (serotonin, 5-HT) transporters to release 5-HT from neurons. However, the effects of these drugs on other monoamine transporters are not well characterized. In this study, we examined the interaction of stereoisomers of (±)-fenfluramine and (±)-norfenfluramine with transporters for 5-HT, norepinephrine (NE), and dopamine (DA). Results from in vitro assays confirmed these drugs are potent substrates for 5-HT transporters: (+)-fenfluramine, (-)-fenfluramine, (+)-norfenfluramine, and (-)-norfenfluramine released [3H]5-HT from synaptosomes with EC50 values of 52, 147, 59, and 287 nM, respectively. Importantly, (+)-fenfluramine and (+)-norfenfluramine released [3H]NE with EC50 values of 302 and 73 nM. Results from in vivo microdialysis experiments showed that intravenous injection of (+)-norfenfluramine elevates extracellular levels of 5-HT, NE, and DA in rat frontal cortex. The effects of (+)-norfenfluramine on NE and DA were antagonized by pretreatment with the NE uptake blocker nisoxetine. In summary, administration of fenfluramines can increase synaptic levels of 5-HT, NE, and DA in the cortex, and (+)-norfenfluramine likely contributes to these effects. Release of NE and DA evoked by (+)-norfenfluramine is at least partly mediated via NE transporters. Our results emphasize the potential involvement of noradrenergic mechanisms in the actions of fenfluramines. The American Society for Pharmacology and Experimental Therapeutics