Seasonal Tanning-Induced Increases in Skin Pigmentation Do Not Affect Nitric Oxide-Mediated Vasodilation of the Cutaneous Microvasculature

Abstract

Acute ultraviolet radiation (UVR) exposure reduces nitric oxide (NO)-dependent cutaneous vasodilation. Additionally, increased constitutive skin melanin concentrations are associated with reduced NO-dependent cutaneous vasodilation. However, the impact of seasonal tanning-induced increases in skin melanin concentration on NO-dependent cutaneous vasodilation has not been investigated. PURPOSE: To investigate the effect of seasonal tanning-induced increases in skin melanin on the NO-dependent cutaneous vasodilation response to local heating. We hypothesized that NO-dependent cutaneous vasodilation would be reduced in tanned skin relative to untanned skin. METHODS: Three intradermal microdialysis fibers were placed in the ventral upper arm (least sun exposed), ventral forearm (moderately sun exposed), and dorsal forearm (most sun exposed) of seven adults (33 ± 14 yrs; 4M/3F) with light-to-moderate constitutive skin pigmentation. Differences in sun exposure among the sites was confirmed using the melanin-index (M-index; an index of skin pigmentation), measured via skin reflectance spectrophotometry. Lactated Ringer’s solution was perfused through the microdialysis fibers while local heating to 42°C induced cutaneous vasodilation. After attaining a stable plateau in cutaneous blood flow, 15mM NG-nitro-L-arginine methyl ester (L-NAME; NO synthase inhibitor) was perfused at all sites to quantify NO-mediated vasodilation. Red cell flux was measured using laser-Doppler flowmetry (LDF). Cutaneous vascular conductance (CVC=LDF/mean arterial pressure) was calculated for each phase of the local heating response (i.e., baseline, initial peak, local heating plateau, post L-NAME plateau) and expressed as percent maximum (%CVCmax; 28mM sodium nitroprusside + 43°C local heating). RESULTS: M-index was highest (i.e., skin pigmentation was darkest) in the dorsal forearm (50.5 ± 11.8 a.u.) compared to the ventral forearm (37.5 ± 7.4 a.u.; p ≤ 0.03) and upper arm (30.2 ± 5.1 a.u.; p ≤ 0.001). There were no baseline (p ≥ 0.37), initial peak (p ≥ 0.22), post L-NAME plateau (p ≥ 0.12), or maximal CVC (p ≥ 0.23) differences among the three sites. Likewise, the magnitude of the local heating plateau was not different among the three sites (dorsal: 88±17%; ventral: 81±20%; upper: 90±12%; p ≥ 0.16), nor was NO-mediated vasodilation (dorsal: 59±15%; ventral: 54±13%; upper: 55±11.0%; p ≥ 0.79). CONCLUSION: These data suggest that, in contrast to the effects of acute UVR exposure or a constitutively dark skin pigmentation, seasonal tanning-induced increases in skin pigmentation do not alter NO-dependent cutaneous vasodilation responses to local heating. This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.