The existence of a local 5-hydroxytryptaminergic system in peripheral arteries.
OBJECTIVE
5-HT is a vasoconstrictor exhibiting enhanced effects in systemic arteries from subjects with cardiovascular disease. The effect of endogenous 5-HT on arteries is controversial, because the concentration of free circulating 5-HT is low and a 5-hydroxytryptaminergic system has not been identified in peripheral arteries. We hypothesized that a local 5-hydroxytryptaminergic system (including 5-HT synthesis, metabolism, uptake and release) with physiological function exists in peripheral arteries.


METHODS
The presence of key components of a 5-hydroxytryptaminergic system in rat aorta and superior mesenteric artery was examined using western blot analyses, immunohistochemistry and immunocytochemistry. The function of the rate-limiting enzyme in 5-HT biosynthesis, tryptophan hydroxylase (TPH), and 5-HT transporter was tested by measuring enzyme activity and 5-HT uptake, respectively. Isometric contraction of arterial strips was used to demonstrate the function of released endogenous 5-HT in arterial tissues.


RESULTS
mRNA for TPH-1 was present in arteries, with low levels of TPH protein and TPH activity. Expression and function of MAO A (5-HT metabolizing enzyme) was supported by immunohistochemistry, western analyses and the elevation of concentrations of 5-hydroxyindoleacetic acid (5-HT metabolite) after exposure to exogenous 5-HT. The 5-HT transporter was localized to the plasma membrane of freshly isolated aortic smooth muscle cells. Peripheral arteries actively took up 5-HT in a time-dependent and 5-HT transporter-dependent manner. The 5-HT transporter substrate, (+)-fenfluramine, released endogenous 5-HT from peripheral arteries, which potentiated noradrenaline-induced arterial contraction.


CONCLUSIONS
This study revealed the existence of a local 5-hydroxytryptaminergic system in peripheral arteries.
Ni
W
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Department of Pharmacology and Toxicology, Michigan State University, East Lansing, MI 48824-1317, USA.
Geddes
T J
TJ
Priestley
J R C
JR
Szasz
T
T
Kuhn
D M
DM
Watts
S W
SW
D000818:Animals; D001013:Aorta, Thoracic / Q000378:metabolism*; D015153:Blotting, Western; D015870:Gene Expression; D007150:Immunohistochemistry; D007537:Isometric Contraction; D008297:Male; D017538:Mesenteric Artery, Superior / Q000378:metabolism*; D008995:Monoamine Oxidase / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D012701:Serotonin / Q000378:metabolism*; D050486:Serotonin Plasma Membrane Transport Proteins / Q000378:metabolism; D013997:Time Factors; D014365:Tryptophan Hydroxylase / Q000378:metabolism
D012333:RNA, Messenger; D050486:Serotonin Plasma Membrane Transport Proteins; D012701:Serotonin; D014365:Tryptophan Hydroxylase; C504570:tph1 protein, rat; D008995:Monoamine Oxidase