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1 Institute for Exercise and Environmental Medicine, Presbyterian Hospital of Dallas, Dallas 75231; and 2 Department of Internal Medicine, University of Texas Southwestern Medical Center, Dallas, Texas 75235
ACh is the neurotransmitter responsible for increasing
sweat rate (SR) in humans. Because ACh is rapidly hydrolyzed by
acetylcholinesterase (AChE), it is possible that AChE contributes to
the modulation of SR. Thus the primary purpose of this project was to
identify whether AChE around human sweat glands is capable of
modulating SR during local application of various concentrations of ACh
in vivo, as well as during a heat stress. In seven subjects, two microdialysis probes were placed in the intradermal space of the forearm. One probe was perfused with the AChE inhibitor neostigmine (10 µM); the adjacent membrane was perfused with the vehicle (Ringer solution). SR over both membranes was monitored via capacitance hygrometry during microdialysis administration of various
concentrations of ACh (1 × 10
7-2 M) and during
whole body heating. SR was significantly greater at the
neostigmine-treated site than at the control site during administration
of lower concentrations of ACh (1 × 10
7-1 × 10
3 M, P < 0.05), but not during
administration of higher concentrations of ACh (1 × 10
2-2 M, P > 0.05). Moreover, the
core temperature threshold for the onset of sweating at the
neostigmine-treated site was significantly reduced relative to that at
the control site. However, no differences in SR were observed between
sites after 35 min of whole body heating. These results suggest that
AChE is capable of modulating SR when ACh concentrations are low to
moderate (i.e., when sudomotor activity is low) but is less effective
in governing SR after SR has increased substantially.
hyperthermia; temperature regulation; microdialysis; neostigmine; acetylcholine
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