Pharmacological analysis of vasoconstrictor responses to periarterial purinergic nerve stimulation

1 Periarterial electrical nerve stimulation at a low frequency (1 Hz) readi ly induced a vasoconstrictor response of the canine splenic artery in a pul se number-related manner (1-30 pulses of trains). The vasoconstrictor respo nse to trains of up to 10 pulses at 1 Hz of stimulation appeared to be mono phasic, whereas it became clearly distinguished into two phases at a longer train of 30 pulses. 2 The monophasic vasoconstrictor responses to trains of 1, 3 or 10 pulses w ere not modified by an alpha(1)-adrenoceptor blocking agent, prazosin (0.1 mu M), but were completely inhibited by the P-2x receptor desensitization w ith alpha,beta-methylene adenosine 5'-triphosphate (alpha,beta-methlyene AT P; 1 mu M). The 1st phase of vasoconstriction induced by a train length of 30 pulses was not influenced by the treatment with prazosin, but was abolis hed by alpha,beta-methylene ATP. The 2nd phase response was markedly inhibi ted by prazosin, and the remaining response of this phase was blocked by al pha,beta-methylene ATP. 3 Rauwolscine (0.3 mu M), an alpha(2)-adrenoceptor antagonist, enhanced the vasoconstrictor responses to trains of 1, 3 or 10 pulses. Particularly at 10 pulses of electrical stimulation, the vasoconstrictor responses were sig nificantly potentiated. The blockade of neuronal uptake of noradrenaline wi th imipramine (1 mu M) did not affect the vasoconstrictor responses to trai ns of 1, 3 or 10 pulses. 4 It is concluded that short pulse trains of stimulation at a low frequency may selectively activate a purinergic component of sympathetic cotransmiss ion, and the prejunctional alpha(2)-adrenergic feedback mechanism may tonic ally participate into the modulation of ATP release. Imipramine-sensitive n euronal uptake mechanism map not play an important role in regulating vascu lar responses to periarterial purinergic nerve stimulation.