Electrically evoked neuropeptide release and neurogenic inflammation differ between rat and human skin

1. Protein extravasation and vasodilatation can be induced by neuropeptides released from nociceptive afferents (neurogenic inflammation). We measured electrically evoked neuropeptide release and concomitant protein extravasa tion in human and rat skin using intradermal microdialysis. 2. Plasmapheresis capillaries were inserted intradermally at a length of 1. 5 cm in the volar forearm of human subjects or abdominal skin of rats. Capi llaries were perfused with Ringer solution at a flow rate of 2.5 or 1.6 mul min(-1). After a baseline period of 60 min capillaries were stimulated ele ctrically (1 Hz, 80 mA, 0.5 ms or 4 Hz, 30 mA, 0.5 ms) for 30 min using a s urface electrode directly above the capillaries and a stainless-steel wire inserted in the capillaries. Total protein concentration was assessed photo metrically and calcitonin gene-related peptide (CGRP) and substance P (SP) concentrations were measured by enzyme-linked immunosorbent assay (ELISA). 3. In rat skin, electrical stimulation increased CGRP and total protein con centration in the dialysate. SP measurements showed a larger variance but o nly for the 1 Hz stimulation was the increased release significant. 4. In human skin, electrical stimulation provoked a large flare reaction an d at a frequency of 4 Hz both CGRP and XP concentrations increased signific antly. In spite of the large flare reactions no protein extravasation was i nduced, which suggests major species differences. 5. It will be of interest to investigate whether the lack of neurogenic pro tein extravasation is also valid under pathophysiological conditions.