Sex differences in postsynaptic sweating and cutaneous vasodilation.

The current study aimed to determine whether a peripheral modulation of sweating contributes to the lower sudomotor thermosensitivity previously observed in females during exercise. We examined dose-response relationships in 12 males and 12 females to incremental doses of acetylcholine (ACh) and methylcholine (MCh) for sweating (ventilated capsule), as well as to ACh and sodium nitroprusside (SNP) for cutaneous vasodilation (laser-Doppler). All drugs were infused using intradermal microdialysis. On a separate day, potential sex differences in the onset threshold and/or thermosensitivity of heat loss responses were assessed during progressive increases in mean body temperature elicited by passive heating. Increases in sweating as a function of increasing concentration of ACh (P = 0.008) and MCh (P = 0.046) significantly differed between males and females. Although the concentration eliciting 50% of the maximal sweating response did not differ between sexes for either agonist (P > 0.1), maximum values were lower in females in response to ACh (0.34 ± 0.12 vs. 0.59 ± 0.19 mg·min(-1)·cm(-2), P = 0.04) and MCh (0.48 ± 0.12 vs. 0.78 ± 0.26 mg·min(-1)·cm(-2), P = 0.05). This observation was paralleled by a lower thermosensitivity of sudomotor activity in females during passive heating (1.29 ± 0.34 vs. 1.83 ± 0.33 mg·min(-1)·cm(-2)·°C(-1), P = 0.03), with no significant differences in the change in mean body temperature at which onset of sweating occurred (0.85 ± 0.19 vs. 0.67 ± 0.13°C, P = 0.10). No sex differences in cutaneous vasodilation were observed in response to ACh and SNP, as well as during passive heating (all P > 0.1). These findings provide direct evidence for a peripheral modulation of sudomotor activity in females. In contrast, sex does not modulate cutaneous vasodilation.