Abstract
Objective: To characterize phenylephrine evoked piloerection physiology. Background Sudomotor and vasomotor axon-reflex responses may be used to assess small fiber function. We have previously reported that piloerection is evoked by phenylephrine iontophoresis beneath the application (direct) site and in the surrounding (indirect) region most likely via an axon-reflex. The mechanism of the indirect response is not fully elucidated. Design/Methods: In this study, twenty subjects participated in 5 studies. Piloerection was stimulated by iontophoresis of 1% phenylephrine and quantified by silicon impressions. In studies 1 and 2, piloerection was measured after application of lidocaine gel and subcutaneous injection of 1% lidocaine-hydrochloride to block the axon reflex. In study 3, to isolate the contribution of ionophoretic current, piloerection was measured after saline iontophoresis. In study 4, the time-course of the piloerection was measured by digital photographing. In study 5, to examine the role played by blood flow, subjects were tested with and without iontophoretic nitroprusside pretreatment. Results: In lidocaine pretreated regions, there were reduced impressions in the indirect area (66.6±19.2 control vs. 7.2±4.3 lidocaine; P Conclusions: These data demonstrate that: The indirect pilomotor response is attenuated by lidocaine consistent with an axon-reflex response; 2)Iontophoresis alone does not induce piloerection; 3)Axon-reflex mediated piloerection is not secondary to vasoconstriction; and 4)Direct and indirect pilomotor responses to phenylephrine have different latencies suggesting different physiological mechanisms. These data are consistent with an axon-reflex mechanism for the pilomotor response and support QPART as a measure of small fiber function. Supported by: NIH; Langer Family Foundation; German Research Foundation. Disclosure: Dr. Siepmann has nothing to disclose. Dr. Illigens has nothing to disclose. Dr. Gibbons has nothing to disclose. Dr. Freeman has received personal compensation for activities with Pfizer Inc, Eli Lilly & Company, GlaxoSmithKline, Inc., Solvay S.A., and Chelsea Pharmaceuticals. Dr. Freeman has received personal compensation in an editorial capacity for Clinical Journal of Pain.
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