The cholinergic blockade of both thermally and non-thermally induced human eccrine sweating
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 (0.04mg kg−1)with thermal clamping sustained;andfollowingclamp 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). 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.