Elevated plasma levels of neuropeptide Y upon electrical stimulation of the sympathetic chain in humans

Neuropeptide Y (NPY) a potent vasoconstrictor peptide, is co-stored with the classic neurotransmitter noradrenaline (NA) in certain peripheral sympathetic neurons and has been suggested to be a co-transmitter in vascular control. Surgical interruption of the sympathetic nerve supply of the upper extremity was performed to treat palmar hyperhidrosis in five patients. Intraoperative electrical stimulation (10 Hz; 0.5 ms; 0.5-3.0 mA) of the right and left sympathetic chains for 1 min was employed to determine the correct level for surgical excision. Blood pressure and heart rate were recorded continuously. Blood was sampled from the antecubital vein on the side subjected to stimulation for the determination of NPY-like immunoreactivity (LI) and plasma catecholamines. Blood samples were collected before and during stimulation, as well as 30 s and 2, 5, and 10 min after stimulation. A maximal blood pressure response was observed during the stimulation, but the magnitude varied markedly and was independent of the side on which the sympathetic chain was stimulated. During 3 of the 10 stimulations, the mean arterial blood pressure (MABP) increased 5-10 mm Hg, while in the other 7 an increase of 30-75 mm Hg was seen. No significant changes in heart rate or plasma adrenaline were found. The peak increase in NPY-LI plasma levels was noted 2 or 5 min after stimulation, while the corresponding peak for NA occurred during or 30 s after the stimulation. The maximal changes in plasma NPY-LI and NA were significantly correlated with the changes in blood pressure (NPY-LI, r = 0.80, p <0.01; NA, r = 0.84, p <0.01) as well as with each other (r = 0.95; p <0.001). It is concluded that, after electrical stimulation of the sympathetic chain in humans, plasma levels of both NPY-LI and NA rise, indicating release of these substances from sympathetic neurons. It is therefore possible that the vasoconstrictor peptide NPY is involved, together with NA, in the blood pressure response elicited by the stimulation.