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 (Twarm = 37.1 ± 0.9°C), control (Tcon = 32.3 ± 1.4°C), and cool (Tcool = 26.6 ± 1.3°C). Tskin was raised and lowered with an electric heating pad and gel ice pack, respectively. Forearm Tskin was measured with a skin temperature probe. Pilocarpine iontophoresis was used on an approximately 7 cm2 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 Twarm (p = 0.001) and Tcon (p = 0.006) compared to that at Tcool. However, there was no difference between the sweat rate at Twarm and that at Tcon (p = 0.127). Conclusion: These results indicated that skin temperatures below approximately 32°C affect local sweat production primarily by altering glandular sensitivity to the neurotransmitter, whereas skin temperatures above approximately 32°C predominantly affect neurotransmitter release. Furthermore, sweat glands display maximal or near maximal cholinergic sensitivity at resting skin temperature in a thermoneutral environment.