Journal
JOURNAL OF APPLIED PHYSIOLOGY
Volume 96, Issue 4, Pages 1380-1384Publisher
AMER PHYSIOLOGICAL SOC
DOI: 10.1152/japplphysiol.00990.2003
Keywords
sympathetic nervous system; axon reflex; laser-Doppler imaging
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In healthy volunteers, flare responses induced by norepinephrine ( NE) iontophoresis have been observed. However, as NE iontophoresis is a combined electrical and chemical stimulus axon, reflexes cannot be directly linked to pharmocological activity of NE. Different concentrations of NE, clonidine (CL), and phenylephrine (PE) ( NE: 10(-10)-10(-3) M; CL and PE: 10(-8)-10(-3) M) were applied via intradermal microdialysis fibers into the skin of healthy volunteers. Simultaneously, skin blood flow was visualized by laser-Doppler imaging scans and quantified in a vasoconstriction skin area directly above the membranes to control drug effects and in expected axon reflex vasodilation areas that were 0.75 cm apart. NE, PE, and CL caused dose-dependent vasoconstriction. However, neither in the presumed axon reflex areas ( quantitative analysis) nor on laser-Doppler imaging pictures ( qualitative analysis) were any vasodilation observed. Even at concentrations causing maximum vasoconstriction ( 10(-3) M for any drug), no vasodilation was induced. Our results indicate that, in healthy human skin, exogenously supplied alpha-adrenoreceptor agonists alone do not activate nociceptors sufficiently to induce axon reflex flare.
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