Effect of Cutaneous Local Axon Reflexes, Perfusion Pressure, and Ischemia on Exogenous Cholinergic-Induced Eccrine Sweating in Humans

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Medicine and Health Sciences


Human skin blood flow (SkBF) and sweating increase similarly during increases in skin sympathetic nerve activity, implicating common control and regulation. Previous studies have blocked sweating without affecting SkBF, but few have altered SkBF without affecting sweating because standard methods such as introducing an α-adrenergic agonist decrease SkBF but also engage receptors on the eccrine sweat gland. Thus, this study was designed to utilize mechanical perturbations to decrease SkBF during intradermal perfusion of a cholinergic agonist. Three intradermal microdialysis fibers were placed in dorsal forearm skin of 1 woman and 3 men (age 24±1 years, BMI 23±3 kg/m2) to perfuse 2 doses of pilocarpine nitrate (0.01 and 1.66 mg/ml, corresponding to the ED50 and EMAX from previous dose-response modeling) or the vehicle (lactated Ringer’s). Forearm SkBF (laser-Doppler flowmetry) was decreased by engaging the venoarteriolar response (arm lowered ~30 cm from heart level; CVAR), venoarteriolar response plus a decrease in perfusion pressure (venous occlusion by proximal cuff inflation; CVAR with DPP), and ischemia (arterial occlusion by proximal cuff inflation) and sweat rate was measured by perfusing anhydrous medical air through a ventilated capsule (capacitance hygrometry). Decreased SkBF was observed with CVAR (58±10, 59±4, and 63±8%), CVAR with DPP (30±13, 22±14 and 37±3%), and ischemia (98±1, 100±2 and 91±3% for the pilocarpine ED50, pilocarpine EMAX, and vehicle control, respectively). Despite these significant decreases in SkBF, changes in eccrine sweat rate were minimal (CVAR = 5±5, 9±4, and 8±6%; CVAR with DPP = 6±8, 1±5, and 7±6%; and ischemia = 5±7, 5±4, and 6±5% for the pilocarpine ED50, pilocarpine EMAX, and vehicle control, respectively). These preliminary data suggest that acute decreases in SkBF do not proportionally decrease cholinergic-induced sweating in human forearm skin. One interpretation of this is independent control and regulation of cutaneous blood vessels and eccrine sweat glands in humans.


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