Prejunctional receptors in human digital arteries

A human digital artery preparation obtained postmortem has been used to study factors influencing 3H-norepinephrine release evoked by periarterial nerve stimulation. Tetrodotoxin nearly abolished the stimulation-induced tritium outflow and the associated vasoconstrictor response. Increasing the frequency of stimulation from 1 to 6 Hz (constant number of 480 pulses) markedly enhanced the stimulation-induced tritium outflow per pulse. Cocaine only modestly increased the outflow. Phentolamine considerably increased, and clonidine significantly decreased, the stimulation-induced tritium outflow, thus indicating the presence of presynaptic alpha-adrenoceptors. Angiotensin also considerably enhanced the stimulation-induced tritium outflow. The results suggest that both frequency of stimulation and presynaptic receptors are of major importance in determining neurotransmitter release in the peripheral vasculature in man.