Evidence for metaboreceptor stimulation of sweating in normothermic and heat-stressed humans

Abstract

1. Isometric handgrip (IHG) exercise increases sweat rate and arterial blood pressure, and both remain elevated during post-exercise ischaemia. The purpose of this study was to identify whether the elevation in arterial blood pressure during post-exercise ischaemia contributes to the increase in sweating. 2. In normothermia and during whole-body heating, 2 min IHG exercise at 40% maximal voluntary contraction, followed by 2 min post-exercise ischaemia, was performed with and without bolus intravenous administration of sodium nitroprusside during the ischaemic period. Sodium nitroprusside was administered to reduce blood pressure during post-exercise ischaemia to pre-exercise levels. Sweat rate was monitored over two microdialysis membranes placed in the dermal space of forearm skin. One membrane was perfused with the acetylcholinesterase inhibitor neostigmine, while the other was perfused with the vehicle. 3. In normothermia, IHG exercise increased sweat rate at the neostigmine-treated site but not at the control site. Sweat rate remained elevated during post-exercise ischaemia even after mean arterial blood pressure returned to the pre-IHG exercise baseline. Subsequent removal of the ischaemia stimulus returned sweat rate to pre-IHG exercise levels. Sweat rate during post-exercise ischaemia without sodium nitroprusside administration followed a similar pattern. 4. During whole-body heating, IHG exercise increased sweat rate at both neostigmine-treated and untreated sites. Similarly, regardless of whether mean arterial blood pressure remained elevated or was reduced during post-exercise ischaemia, sweat rate remained elevated during the ischaemic period. 5. These results suggest that sweating in non-glabrous skin during post-IHG exercise ischaemia is activated by metaboreflex stimulation and not via baroreceptor loading.

Figure 2. Influence of isometric exercise on sweating rate during whole-body heating

During whole-body heating, isometric exercise increased sweating rate (SR) at both neostigmine-treated and untreated sites. Sweat rate remained elevated during post-exercise ischaemia (PEI) at both sites regardless of whether mean arterial blood pressure (MAP) was returned to baseline during PEI. * Significantly different from baseline (P < 0.05).

Figure 1. Influence of isometric exercise on sweating rate in normothermia

In normothermia, isometric exercise increased sweating rate (SR) at the neostigmine-treated site but not at the control site. Sweat rate remained elevated during post-exercise ischaemia (PEI) at the neostigmine-treated site regardless of whether mean arterial blood pressure (MAP) remained elevated during PEI (left panel) or was reduced via bolus infusion of sodium nitroprusside (right panel; see arrow). * Significantly different from baseline (P < 0.05).