SPATIAL EXTENSION OF SUDOMOTOR AXON REFLEX SWEATING IN HUMAN SKIN

Acetylcholine (ACh) applied to human skin is known to elicit a sweat r esponse, which consists of a direct muscarinergic (M3) activation of s weat glands and a nicotinic axon reflex response ron; sudomotor termin als. To visualize the extent of axon reflex sweating after ACh-iontoph oresis, iodine starch staining was used. Iontophoresis was performed u nder occlusion at the peroneal aspects of the lower leg and the center of the foot dorsum of healthy volunteers (n = 10). Ten minutes after stimulation, the area of dark blue staining was recorded by a video ca mera. Control experiments were performed with saline, histamine, piloc arpine and nicotine iontophoresis. The stained area was measured and t he maximum and minimum distance of its boundary from the edge of the i ontophoresis probe was determined (maximum/minimum radius). Sizes of s tained areas and maximum radii were significantly greater on the lower leg compared to the foot (P < 0.01). The median sizes of the stained areas on the leg were 14.6 cm(2) and on the foot dorsum 8.0 cm(2). The respective median maximum radii were 3.1 cm on the leg and 2.3 cm on the foot dorsum (median minimum, leg 1.1 cm, foot 0.8 cm). These resul ts match microneurographic findings of innervation territories of symp athetic efferent units. Area sizes of stained skin showed a close corr elation between both stimulation sites (R = 0.96, P < 0.01), i.e, the sizes of sweat responses on leg and foot show a constant relation (foo t/leg = 0.57) in spite of their great interindividual variability. :Th is novel technique of establishing sweat responses provides informatio n on the size of sudomotor innervation territories and may be useful f or clinical studies in patients with suspected impairment of sympathet ic functions. (C) 1998 Elsevier Science B.V. All rights reserved.