Effect of skin temperature on the cholinergic sensitivity of the human eccrine sweat gland

Although sweat gland activity is directly controlled by the central nervous system, which detects changes in core body temperature, sweat glands can also be influenced by local cutaneous thermal conditions. Objective: The present study sought to determine the effect of local skin temperature on pilocarpine-induced sweating within a range of typical skin temperatures. Methods: Thirteen subjects (30+/-6 years; 172+/-11 cm; 72.8+/-11.0 kg) had forearm sweat rates measured at rest following pilocarpine iontophoresis at each of three skin temperatures in randomized order: warm (T-warm=37.1+/-0.9degreesC), control (T-con=32.3+/-1.4degreesC), and cool (T-cool= 26.6+/-1.3degreesC). T-skin was raised and lowered with an electric heating pad and gel ice pack, respectively. Forearm T-skin was measured with a skin temperature probe. Pilocarpine iontophoresis was used on an approximately 7 cm(2) area of the anterior forearm to stimulate localized sweating. Following stimulation, sweat was collected from the area for 15 min with a Macroduct Sweat Collection System. Results: There was a higher sweat rate at T-warm (p=0.001) and T-con (p=0.006) compared to that at T-cool. However, there was no difference between the sweat rate at T-warm and that at T-con (p=0.127). Conclusion: These results indicated that skin temperatures below approximately 32degreesC affect local sweat production primarily by altering glandular sensitivity to the neurotransmitter, whereas skin temperatures above approximately 32degreesC predominantly affect neurotransmitter release. Furthermore, sweat glands display maximal or near maximal cholinergic sensitivity at resting skin temperature in a thermoneutral environment.