The effects of 5-hydroxytryptamine (5-HT), 5-carboxamidotryptamine, and sumatriptan on rat caudal arteries were examined, with the goal of finding experimental conditions useful in enhancing the ‘silent’ 5-HT1B receptor subtype. It was shown that both reserpine treatment and K+ depolarizationincreased the vasoconstriction by 5-HT receptor agonists. The role of the 5-HT2A receptor in vasoconstriction was examined using ritanserin (50 nmol/l), a selective 5-HT2A antagonist, whereas that of the ‘silent’ 5-HT1B receptor was examined using SB-224289 (0.2 µmol/l), a selective 5-HT1B receptor antagonist. The influence of age on the ‘silent’ 5-HT1B receptor subtype was also investigated; for this, the effect of sumatriptan, a selective 5-HT1B/1D agonist, was tested on arterial tissues of both young and old rats which had been either K+ depolarized or reserpine treated or both. It was found that aging strongly shifted the concentration-vasoconstriction curve generated by sumatriptan to the left, also increasing the maximum contractile response, mainly in reserpine-treated tissues. RT-PCR was used to study the expression of 5-HT1B and 5-HT2A receptors in both young and old tissues. The results support the idea that reserpine-treated and K+-depolarized caudal arteries from old rats can be a pharmacological model which is useful in highlighting the ‘silent’ 5-HT1B receptor subtype.

Keywords:
‘Silent’ 5-HT1B receptor, 5-HT2A receptor, Aging, rat resistance vessels, Sumatriptan, Caudal artery
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© 2008 S. Karger AG, Basel
2007
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