Modulation of muscle metaboreceptor activation upon sweating and cutaneous vascular responses to rising core temperature in humans

Abstract

The present study investigated the role of muscle metaboreceptor activation on human thermoregulation by measuring core temperature thresholds and slopes for sweating and cutaneous vascular responses during passive heating associated with central and peripheral mechanisms. Six male and eight female subjects inserted their lower legs into hot water (43°C) while wearing a water perfusion suit on the upper body (34°C). One minute after immersion, an isometric handgrip exercise--40% of maximum voluntary contraction-was conducted for 1.5 min in both control and experimental conditions, while postexercise occlusion was performed in the experimental condition only for 9 min. The postexercise forearm occlusion during passive heating consistently stimulated muscle metaboreceptors, as implicated by significantly elevated mean arterial blood pressure throughout the experimental period (P <0.05). Stimulation of the forearm muscle metaboreceptors increased sweating and cutaneous vascular responses during passive heating, and was associated with significant reductions in esophageal temperature threshold of sweating and cutaneous vasodilation (Δ threshold, sweating: 0.33 ± 0.05 and 0.16 ± 0.04°C, cutaneous vascular conductance: 0.38 ± 0.08 and 0.16 ± 0.05°C for control and experimental groups, respectively, P < 0.05). The slopes of these responses were not different between the conditions. These results suggest that muscle metaboreceptor activation in the forearm accelerates sweating and cutaneous vasodilation during passive heating associated with a reduction in core temperature thresholds and may be related to central mechanisms controlling heat loss responses.

The mechanisms underlying the muscle metaboreflex modulation of sweating and cutaneous blood flow in passively heated humans

“…However, this response differed from their previous observations during passive heating (Amano et al. ). In the context of our findings, our study informs the possible mechanisms mediating this response during exercise.…”

“…Importantly, a recent report by Amano et al (2016) studied the contribution of the metaboreflex on the heat loss responses during dynamic exercise and demonstrated that the activation of metaboreceptors augments sweating but does not affect cutaneous vascular responses. However, this response differed from their previous observations during passive heating (Amano et al 2015). In the context of our findings, our study informs the possible mechanisms mediating this response during exercise.…”

“…Additionally, further studies are required to assess these mechanism(s) for a longer duration of metaboreceptors activity (Amano et al. , ) and or intensity/duration of IHG exercise paradigms (Crandall et al. , ; Kondo et al.…”

“…As such, future studies are necessary to extend upon this work. Additionally, further studies are required to assess these mechanism(s) for a longer duration of metaboreceptors activity (Amano et al 2015(Amano et al , 2016 and or intensity/ duration of IHG exercise paradigms Kondo et al 2000Kondo et al , 2003Shibasaki et al 2001). All of the aforementioned factors may influence the level of metaboreflex activation and therefore the relative contribution of these different mediators.…”

“…In humans, the heat loss responses of cutaneous blood flow and sweating are important in the regulation of core temperature during heat stress. It is well documented that these responses can also be modulated by nonthermal muscle metaboreceptors Kondo et al 1999;McGinn et al 2014c;Amano et al 2015Amano et al , 2016Paull et al 2015). Specifically, metaboreflex activation, achieved by isometric handgrip (IHG) exercise followed by forearm ischemia to trap the produced metabolites, stimulates reductions in cutaneous vascular conductance (CVC) during hyperthermia, which is associated with a withdrawal of cholinergic vasodilator nerve activity Shibasaki et al 2009).…”