Release of acetylcholine during whole‐body heating in aged skin

Abstract

Sweat rate (SR) to a whole‐body heat stress is attenuated in aged skin. Possible mechanisms of this attenuation are 1) reduced neural signaling, 2) attenuated release of neurotransmitter, and/or 3) decreased sweat gland responsiveness to acetylcholine (ACh). We tested the hypothesis that attenuated release of ACh in aged skin may contribute to decreases in sweating during a heat stress. Intradermal microdialysis probes were placed in dorsal forearm and lower leg skin in 8 young (22±1 yrs) and 7 old (70±1 yrs) healthy subjects. Local SR was measured over the microdialysis membranes by the ventilated capsule method. Ringerˈs solution containing 10mM of the acetylcholinesterase inhibitor neostigmine was perfused through each membrane (perfusion rate: 2 μl/min) and the effluent was collected at 8 min increments. ACh in the effluent was measured by high‐pressure liquid chromatography combined with electrochemical detector. Whole‐body heating increased tympanic temperature ~ 1.2°C. Throughout the heat stress SR was lower in the aged group, whereas the release of ACh was similar between groups at both forearm and leg sites. Therefore the SR/ACh ratio in the 20 μl sample was significantly lower in the aged group (Forearm: 0.10±0.07 vs 0.21±0.11 mg/cm2/min/fmol, Leg: 0.10±0.06 vs 0.25±0.13 mg/cm2/min/fmol, both P<0.05). These results suggest that the age‐related reduction in SR is not due attenuated release of ACh.