Repeated cycles of electrical stimulation decrease vasoconstriction and axon‐reflex vasodilation to noradrenaline in the human forearm

Open Access
Publisher Website
Google Scholar
Abstract
What is already known about this subject • Repeated cycles of electrical stimulation inhibit cutaneous vasoconstriction to noradrenaline, but the mechanism is unknown.• Investigating this is important because peripheral electrical stimulation is useful for pain modulation and appears to assist cutaneous wound healing. What this study adds • Intermittent, brief electrical stimulation of the forearm over a 10‐day period inhibited vasoconstriction and axon‐reflex vasodilation to noradrenaline, but did not affect vasoconstriction to vasopressin or axon‐reflex vasodilation to histamine.• Thus, electrical stimulation may evoke a specific reduction in responsiveness to noradrenaline.Aim: To investigate whether desensitization to the vasomotor effects of noradrenaline is a specific effect of electrical stimulation.Methods: Three sites on the forearm of 10 healthy volunteers were stimulated with 0.2 mA direct current for 2 min twice daily for 10 days. Noradrenaline and histamine were then displaced from ring‐shaped iontophoresis chambers into two of the pretreated sites and two untreated sites on the contralateral forearm. Axon‐reflex vasodilation was measured from the centre of the ring described by the iontophoresis chamber with a laser Doppler flowmeter. One or two days later, noradrenaline and vasopressin were introduced into pretreated and untreated sites by iontophoresis, and vasoconstriction at sites of administration was measured in the heated forearm.Results: The pretreatment blocked vasoconstriction to noradrenaline [median increase in flow 1%, interquartile range (IR) −41 to 52%; median decrease at the untreated site 53%, IR. −70 to −10%; P < 0.05], but did not block vasoconstriction to vasopressin (median decrease 42% at the untreated site and 45% at the pretreated site). Axon‐reflex vasodilation to noradrenaline was diminished at the pretreated site (median increase in flow 33%, IR 2–321%; untreated site 247%, IR 31–1087%; P < 0.05). However, axon‐reflex vasodilation to histamine did not differ significantly between the pretreated site (median increase 1085%) and the untreated site (median increase 1345%).Conclusions: The conditioning pretreatment appears to evoke a specific decrease in responsiveness to noradrenaline. Repeated cycles of electrical stimulation may downregulate neural and vascular responses to noradrenaline by repetitively activating cutaneous sympathetic nerve fibres.

This publication has 34 references indexed in Scilit: