The cholinergic blockade of both thermally and non‐thermally induced human eccrine sweating

Abstract

Thermally induced eccrine sweating is cholinergically mediated, but other neurotransmitters have been postulated for psychological (emotional) sweating. However, we hypothesized that such sweating is not noradrenergically driven in passively heated, resting humans. To test this, nine supine subjects were exposed to non-thermal stimuli (palmar pain, mental arithmetic and static exercise) known to evoke sweating. Trials consisted of the following four sequential phases: thermoneutral rest; passive heating to elevate (by ∼1.0• C) and clamp mean body temperature and steady-state sweating (perfusion garment and footbath); an atropine sulphate infusion (0.04 mg kg −1 ) with thermal clamping sustained; and following clamp removal. Sudomotor responses from glabrous (hairless) and non-glabrous skin surfaces were measured simultaneously (precursor and discharged sweating). When thermoneutral, these non-thermal stimuli elicited significant sweating only from the palm (P < 0.05). Passive heating induced steady-state sweating ranging from 0.20 ± 0.04 (volar hand) to 1.40 ± 0.14 mg cm −2 min −1 (forehead), with each non-thermal stimulus provoking greater secretion (P < 0.05). Atropine suppressed thermal sweating, and it also eliminated the sudomotor responses to these nonthermal stimuli when body temperatures were prevented from rising (P > 0.05). However, when the thermal clamp was removed, core and skin temperatures became further elevated and sweating was restored (P < 0.05), indicating that the blockade had been overcome, presumably through elevated receptor competition. These observations establish the dependence of both thermal and non-thermal eccrine sweating from glabrous and non-glabrous surfaces on acetylcholine release, and challenge theories concerning the psychological modulation of sweating. Furthermore, no evidence existed for the significant participation of non-cholinergic neurotransmitters during any of these stimulations.

The effect of plasma osmolality and baroreceptor loading status on postexercise heat loss responses

“…However, although a subjective index of thermal sensation was not measured, participants in the present study anecdotally reported greater comfort during LBPP application. Considering that eccrine sweating can be modulated by the level of emotional and/or perceived stress (25,26), it is plausible that sweat rate was reduced during LBPP application as a result of an attenuated level of mental stress. Further, this observation in our study, as well as in the study by McGinn et al (27), is only reported in the final 30 min of recovery, wherein core temperature had recovered to ϳ37.5°C.…”

Regional variations in transepidermal water loss, eccrine sweat gland density, sweat secretion rates and electrolyte composition in resting and exercising humans

“…Indeed, his text also shows an awareness of the differences in sweat secretion from the glabrous (hairless) and non-glabrous (hairy) surfaces of these appendages, and the Dutch microbiologist Antonie van Leeuwenhoek (1632–1723) also wrote about sweating [18] and the sweat pores of the hands [19]. However, the precise control of sweat glands from these glabrous surfaces has, until recently, remained unresolved [15,20,21]. …”

Brain stem representation of thermal and psychogenic sweating in humans

“…The main nonthermal drive to sweating in resting individuals is mental stress or arousal, referred to here as psychogenic sweating (32). Despite earlier doubts (39,48), it now seems clear that cholinergic sympathetic nerves are the final motor pathways for both thermal and psychogenic sweating (31) and that both types of sweating occur over the whole body rather than being restricted to certain skin areas (32,33). It is probable (though not yet formally proven) that the same individual sympathetic neurons mediate these responses via common sudomotor units during both thermal and nonthermal sudomotor drives.…”