ISSN:
1440-1681
Source:
Blackwell Publishing Journal Backfiles 1879-2005
Topics:
Medicine
Notes:
1. The vasoconstrictor responses of canine gastroepiploic artery to periarterial electrical nerve stimulation (PNS; 30 s trains of pulses at a frequency of 2, 4 or 8 Hz) were observed in a frequency dependent manner. The PNS-induced vasoconstrictions were abolished by tetrodotoxin (1 µmol/L) and mostly depressed but not completely by guanethidine (10 µmol/L).2. Vasoconstrictor responses to administered noradrenaline were antagonized significantly by prazosin (0.1 µmol/L), an α1-adrenoceptor antagonist, but were not significantly affected by suramin (100 µmol/L), a P2 purinoceptor antagonist, or α,β-methylene ATP (1 µmol/L), a P2X receptor desensitizing agent. Exogenous ATP-induced responses were clearly depressed by suramin or α,β-methylene ATP, but were not significantly affected by prazosin.3. The vasoconstrictor responses to PNS at a low frequency (2 and 4 Hz) of stimulation were markedly inhibited by suramin (100 µmol/L) and by α,β-methylene ATP (1 µmol/L). The remaining responses after suramin or α,β-methylene ATP were abolished by subsequent application of prazosin (0.1 µmol/L). At a high frequency (8 Hz) of stimulation, the vascular response was not significantly inhibited by suramin or α,β-methylene ATP, but it was abolished by prazosin.4. Injection of xylazine (0.3–30 nmol/L), an α2-adrenoceptor agonist, did not induce any clear vasoconstriction. The exposure of tissues to rauwolscine (0.1–0.3 µmol/L), an α2-adrenoceptor antagonist, dose-dependently increased PNS-induced vasoconstrictions at all frequencies tested.5. The present results indicate that ATP acts as a cotransmitter with noradrenaline and is responsible for post-junctional vasoconstrictor responses at low frequencies of sitmulation, whereas the effect of noradrenaline is dominant at high-frequency stimulation in canine gastroepiploic artery. Prejunctional α2-adrenoceptor autoinhibition may modulate the release of either noradrenaline or ATP from sympathetic nerve terminals.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1046/j.1440-1681.2003.03897.x
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