(+)-Norfenfluramine-induced arterial contraction is not dependent on endogenous 5-hydroxytryptamine or 5-hydroxytryptamine transporter.
(+)-Norfenfluramine, the major metabolite of fenfluramine, causes vasoconstriction dependence on the 5-hydroxytryptamine (5-HT)(2A) receptor in rat. (+)-Norfenfluramine was reported as a 5-hydroxytryptamine transporter (5-HTT) substrate and 5-HT releaser. Because the arterial 5-HTT exists and is functional in the rat, we hypothesized that (+)-norfenfluramine causes vasoconstriction by releasing 5-HT from vascular smooth muscle via 5-HTT. The released 5-HT, in turn, activates the 5-HT(2A) receptor. Isometric contractility experiments showed that (+)-norfenfluramine-induced mouse aortic contraction was reduced by the 5-HTT inhibitor fluoxetine (1 micriM) but not by fluvoxamine (1 microM). Tryptophan hydroxylase (TPH)-deficient (Tph1-/-) mice lack peripheral 5-HT. (+)-Norfenfluramine (10 nM-100 microM)-contracted aorta from wild-type and Tph1-/- mice with equivalent potency (-log EC(50) [M], wild type = 5.73 +/- 0.02, Tph1-/- = 5.62 +/- 0.09), and these contractions were inhibited by the 5-HT(2A) receptor antagonist ketanserin (3 nM) by a similar magnitude in aorta from wild-type and Tph1-/- mice (wild type = 19.4, Tph1-/- = 15.4-fold rightward shift versus control), as did fluoxetine (1 microM) (wild type = 22.4, Tph1-/- = 28.8-fold rightward shift versus control). To further test the role of 5-HTT in (+)-norfenfluramine-induced aortic contraction, the 5-HTT-targeted mutation mouse was used. (+)-Norfenfluramine induced similar aortic contraction in wild-type and 5-HTT-targeted mutation mice, and these contractions were inhibited by fluoxetine (1 microM). Thus, (+)-norfenfluramine vasoconstriction is not dependent on 5-HTT-mediated release of endogenous 5-HT but by activating membrane 5-HT(2A) receptors directly. Understanding of the mechanism by which (+)-norfenfluramine induces vasoconstriction is important to characterize and understand the function of the serotonergic system in peripheral arterial vasculature.
Ni
Wei
W
Department of Pharmacology and Toxicology, Michigan State University, East Lansing, 48824-1317, USA. niwei@msu.edu
Wilhelm
Claudia S
CS
Bader
Michael
M
Murphy
Dennis L
DL
Lookingland
Keith
K
Watts
Stephanie W
SW
D000818:Animals; D001011:Aorta / Q000737:chemistry / Q000187:drug effects* / Q000502:physiology; D005473:Fluoxetine / Q000494:pharmacology; D016666:Fluvoxamine / Q000494:pharmacology; D007650:Ketanserin / Q000494:pharmacology; D008297:Male; D008562:Membrane Glycoproteins / Q000032:analysis / Q000502:physiology*; D026901:Membrane Transport Proteins / Q000032:analysis / Q000502:physiology*; D051379:Mice; D008810:Mice, Inbred C57BL; D009419:Nerve Tissue Proteins / Q000032:analysis / Q000502:physiology*; D009642:Norfenfluramine / Q000494:pharmacology*; D012701:Serotonin / Q000032:analysis / Q000502:physiology*; D050486:Serotonin Plasma Membrane Transport Proteins; D017367:Selective Serotonin Reuptake Inhibitors; D014365:Tryptophan Hydroxylase / Q000502:physiology; D014661:Vasoconstriction / Q000187:drug effects*
D005473:Fluoxetine; D016666:Fluvoxamine; D007650:Ketanserin; D008562:Membrane Glycoproteins; D026901:Membrane Transport Proteins; D009419:Nerve Tissue Proteins; D009642:Norfenfluramine; D012701:Serotonin; D050486:Serotonin Plasma Membrane Transport Proteins; D017367:Selective Serotonin Reuptake Inhibitors; D014365:Tryptophan Hydroxylase; C493231:Slc6a4 protein, mouse; C487801:Tph1 protein, mouse