Mechanisms and time course of menthol-induced cutaneous vasodilation

Menthol is a vasoactive compound that is widely used in topical analgesic agents. Menthol induces cutaneous vasodilation, however the underlying mechanisms are unknown. Determining the rates of appearance and clearance of menthol in the skin is important for optimizing topical treatment formulation and dosing. The purpose of this study was to determine the mechanisms contributing to menthol-mediated cutaneous vasodilation and to establish a time course for menthol appearance/clearance in the skin. Ten young (23 +/- 1 years, 5 males 5 females) subjects participated in two protocols. In study 1, four intradermal microdialysis fibers were perfused with increasing doses of menthol (0.1-500 mM) and inhibitors for nitric oxide (NO), endothelium derived hyper polarizing factors (EDHFs), and sensory nerves. Skin blood flow was measured with laser Doppler flowmetry and normalized to %CVCmax. In study 2, two intradermal microdialysis fibers were perfused with lactated Ringer's solution. 0.017 mL.cm(-2) of a 4% menthol gel was placed over each fiber. 5 mu L samples of dialysate from the micro dialysis fibers were collected every 30 min and analyzed for the presence of menthol with high performance gas chromatography/mass spectrometry. Skin blood flow (laser speckle contrast imaging) and subjective ratings of menthol sensation were simultaneously obtained with dialysate samples. In study 1, menthol induced cutaneous vasodilation at all doses >= 100 mM (all p < 0.05). However, inhibition of either NO, EDHFs, or sensory nerves fully inhibited menthol-mediated vasodilation (all p>0.05). In study 2, significant menthol was detected in dialysate 30 min post menthol application (0.89 ng, p = 0.0002). Relative to baseline, cutaneous vasodilation was elevated from minutes 15-45 and ratings of menthol sensation were elevated from minute 5-60 post menthol application (all p < 0.05). Menthol induces cutaneous vasodilation in the skin through multiple vasodilator pathways, including NO, EDHF, and sensory nerves. Topical menthol is detectable in the skin within 30 min and is cleared by 60 min. Skin blood flow and perceptual measures follow a similar time course as menthol appearance/clearance. (C) 2016 Elsevier Inc. All rights reserved.