Failure to influence the VIP level in the cerebrospinal fluid by transcutaneous nerve stimulation in humans

Low-frequency transcutaneous nerve stimulation (TNS) is known to produce a prolonged and widespread cutaneous vasodilatation. This is associated with a moderate but significant increase of 30-35% in the concentration of the vasoactive intestinal polypeptide (VIP) in the cubital vein plasma. A possible source of this increased plasma VIP following TNS is the central nervous system. This possibility is tested in the present experiment. The concentration of VIP in the cerebrospinal fluid (CSF) was determined by radioimmunoassay in 9 patients with no organic disease of the central nervous system, before and at various intervals (15, 30 and 45 min) after the onset of TNS. No significant change in the VIP level of the cerebrospinal fluid was encountered, although the stimulation evoked rises in finger temperature indicating effectiveness of the stimulation. It is concluded that the stimulation-induced increase in plasma VIP is due to release of VIP outside the brain.