The Vasodilatory Response of Skin Microcirculation to Local Heating is Subject to Desensitization

Background: In humans, local heating increases skin perfusion by mechanisms dependent on nitric oxide (NO). Because the vascular effects of NO may be subject to desensitization, we examined whether a first local thermal stimulus would attenuate the hyperemic response to a second one applied later. Methods: Twelve healthy young men were studied. Skin blood flow (SkBF) was measured on forearm skin with laser Doppler imaging. Local thermal stimuli (temperature step from 34 to 41°C maintained for 30 minutes) were applied with temperature-controlled chambers. We also tested the influence of prior local heating on the vasodilation induced by sodium nitroprusside (SNP), a donor of NO. Results: On reheating the same spot after two hours, the response of SkBF (i.e., plateau SkBF at 30 minutes minus SkBF at 34°C) was lower than during the first stimulation (mean±SD 404±212 perfusion units [PU] vs. 635±100 PU; P<0.001). There was no such difference when reheating after four hours (654±153 vs. 645±103 PU; P=NS). Two, but not four, hours after local heating, the response of SkBF to SNP was reduced. Conclusion: The NO-dependent hyperemic response induced by local heating in human skin is subject to desensitization. At least one part of the mechanism implicated consists of a desensitization to the effects of NO itself.