Xiao-Ping Yang and Shigetoshi Chiba (*)
Department of Pharmacology, Shinshu University School of Medicine, Matsumoto
390-8621, Japan
(*) To whom correspondence should be addressed.
Abstract: Using a cannula insertion method, periarterial nerve
electrical stimulations were performed at 1 and 10 Hz in the isolated, perfused
canine splenic artery. Electrical nerve stimulation readily caused double-peaked
vasoconstrictions. The 1st-peak response at 1 Hz was not influenced by treatment
with imipramine but the 2nd one was significantly enhanced by it. The 2nd-peak
response was markedly blocked by prazosin. An additional treatment with
alpha,beta-methylene ATP, a P2X-purinoceptor desensitizer, abolished electrical
stimulation-induced vascular responses that remained. At 10 Hz, the responses
to electrical stimulation were not significantly influenced by imipramine.
On the other hand, the imipramine treatment inhibited the tyramine-induced
vasoconstriction but potentiated the noradrenaline-induced one. ATP-induced
responses were not modified by imipramine. From these results, it is concluded
that 1) the 1st-peaked constriction is mainly due to a P2X-purinoceptor-dependent
mechanism, 2) the 2nd one is mainly due to an alpha1-adrenoceptor-dependent
mechanism, and 3) presynaptic uptake mechanisms may perform an important
role in the regulation of vascular reactivity, especially at a low frequency.
Keywords: Dog splenic artery, Cannula insertion method, Imipramine, Periarterial
nerve stimulation, alpha,beta-Methylene ATP