| Keywords |
ACh ; Thermoregulation ; Iontophoresis ; Sudomotor axon reflex ; Sweating |
| Abstract |
Efferent sweat fibers originate in the centrally sweat regulated by preoptic area and anterior hypothalamic, as well as peripherally, and descend through the ipsilateral brainstem and medulla to synapse with the intermediolateral cell column neurons. To determine the centrally and peripheral sudomotor mechanisms involved in thermal sweating during at the before and after exposure of 21 times (43oC water immersion of leg/30 min/1 times/day), we evaluated the sweating responses to acetylcholine (ACh), a primary neurotransmitter involved in peripheral sudomotor sensitivity, in healthy male subjects (n=8). The quantitative sudomotor axon reflex test (QSART) measures sympathetic C fibre function when iontophoresed ACh evokes a measurable reliable sweat response. QSART, by 2 mA for 5 min with 10% ACh, was applied to determine the directly activated (DIR) and axon reflex-mediated (AXR) sweating response during ACh iontophoresis. The AXR sweat onset-time by the axon reflex was 1.53±0.42 min and 1.86±0.41 min at the before and after exposure, respectively (P<0.01). The sweat volume of AXR (1) by the axon reflex was 1.19±0.57 mg/cm2 and 0.71±0.23 mg/cm2 at the before and after exposure, respectively (P<0.001). The sweat volume of the AXR (2) sweat volume by the axon reflex was 1.95±0.46 mg/cm2 and 1.25±0.27 mg/cm2 at the before and after exposure, respectively (P<0.001). The sweat volume of DIR was 5.32±1.24 mg/cm2 and 4.08±1.19 mg/cm2 at the before and after exposure, respectively (P<0.01). These results indicate that the exposure to hot acclimatization resulted in a lower sweat output due to the combination of a lower sweat volume (AXR and DIR) and a delayed action of the onset time for the AXR. These findings suggest that lower peripheral sudomotor responses to ACh receptors are indicative of blunted sympathetic nerve responsiveness to ACh sensitivity with exposure to hot environmental conditions. |