[ATP as a periarterial sympathetic transmitter in isolated vessel]

Double-peaked vasoconstrictor responses to periarterial nerve electrical stimulation (PNS) were readily induced in the condition of 30-s trains of pulses in isolated, perfused canine splenic artery, using the cannula insertion technique. P2X Prinoceptors have been shown to be involved mainly in the 1st peak response and alpha 1-adrenoceptors mostly in the 2nd one. A small dose of TTX did not affect the 1st peak, but strongly inhibited the 2nd one, although larger doses of TTX diminished either the 1st or 2nd response. A small dose of guanethidine also inhibited only the 2nd one. The 1st one was inhibited by prolonged cold storage of the vessel. On the other hand, omega CT produced parallel inhibitory effects on the 1st and 2nd peaked responses. A low pulse number of ES only caused the release of purinergic transmitters from sympathetic nerve terminals. The possible role as a transmitter of ATP is discussed in periarterial sympathetic transmission.