Topical Ilex Application Increases Skin Blood Flow

Open Access
Author:
Conlon, Christian Clarke
Area of Honors:
Biology
Degree:
Bachelor of Science
Document Type:
Thesis
Thesis Supervisors:
  • Lacy Marie Alexander, Thesis Supervisor
  • James Harold Marden, Honors Advisor
Keywords:
  • Biofreeze
  • ilex
  • menthol
  • skin blood flow
  • microvascular function
Abstract:
Biofreeze is a commercially available topical analgesic. It is primarily used for its ability to induce cooling sensations mediated by the active ingredient menthol. In addition to menthol, ilex is a putatively inactive ingredient that is purported to act as a skin conditioner and enhance permeability to menthol. Both menthol and ilex are plant extracts, with menthol activating TRPM8 receptors in blood vessel walls and ilex postulated to have dilatory influences on blood vessels. The aim of this study was to examine the separate and combined effects of menthol and ilex on cutaneous vasoreactivity. Cutaneous blood flow was assessed at four sites (1. Biofreeze, 2. Menthol, 3. Ilex, 4. Control) using reactive hyperemia (RH) (5 minute occlusion) and local heating to induce endothelium derived hyperpolarizing factor (EDHF)-mediated and nitric oxide (NO)-mediated vasodilation, respectively. Skin blood flow (SkBF) was measured using laser speckle contrast imaging (moorFLPI) on the forearm skin. For the reactive hyperemia protocol the total hyperemic response (THR = AUC - [(baseline SkBF as %maximal cutaneous vascular conductance CVCmax) x duration of hyperemic response in s]) was calculated through integration over the hyperemic response above occlusion blood flow and normalized to cutaneous vascular conductance (CVC=Flux/MAP) and expressed as a percentage of maximal CVC (%CVCmax). %CVCmax was calculated and analyzed for the local heating protocols. All protocols were repeated on the opposite arm after topical 5% lidocaine application (LMX 5 cream) to inhibit sensory nerves. Baseline skin blood flow was increased in the Biofreeze and ilex gel sites (P<0.01) with no significant changes at the menthol site. Similarly, Ilex application increased the local heating plateau (P=0.04). The THR increased with the application of ilex gel (P<0.01) and Biofreeze (P<0.01) (217% increase over placebo). Skin blood flow with Biofreeze and ilex gels after lidocaine application was partially attenuated (26% and 47% decrease respectively), yet continued to be elevated over menthol and placebo sites (P<0.01). These results suggest that menthol stimulates cold sensation yet has little effect upon cutaneous vasomotor tone, whereas the ilex increases skin blood flow likely through EDHF and NO-dependent mechanisms.