Abstract
Intradermal microdialysis and laser Doppler velocimetry were combined to evaluate neurogenic control of vasomotor activity of human skin blood vessels during non-painful intradermal electrical stimulation (E-stim). The laser Doppler flow probe was mounted directly over the microdialysis probe and the stimulating electrodes penetrated the skin 2 mm with the electrode tips separated by ≈ 4 mm. E-stim consisted of a constant current (1.8 ± 0.2 mA) pulses delivered at increasing frequency (0.2, 1, 2, 4, 8, and 32 Hz) in one minute steps. Stimulus- response curves of frequency versus skin blood flow (SkBF) were constructed and the area under the SkBF-time response curve was calculated. During saline perfusion increasing stimulus frequencies cause progressively greater reductions in SkBF with significant declines from baseline observed at frequencies of ≥2 Hz (p<0.05). The peak reduction in SkBF at 32 Hz was represented by an AUC of −2566 ± 854 SkBF·sec. In contrast, following adrenergic blockade (phentolamine (0.05 mg/ml), propranolol (1 mM), and BIBP-3226 (10 μM) SkBF failed to decline below baseline and the AUC at 32 Hz averaged only −342 ± 540 SkBF·sec (p<0.05). These data support the hypothesis that non-painful E-stim protocol provided a significant activation of the local sympathetic vasoconstrictor nerves and may provide a novel approach to investigating active cutaneous vasodilation.
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