Baroreceptors and thermal state modulate metaboreceptor reductions in local heat loss responses

Abstract

Studies show that activation of muscle metaboreceptors following isometric hand grip exercise (IHG) attenuates local sweating (LSR) and cutaneous vascular conductance (CVC). It is unclear however if: 1) concomitant changes in baroreceptor loading status and/or, 2) the level of thermal stress modulates this response. Twelve males performed 1-min of IHG at 60% of maximal voluntary contraction followed by 2-min of ischemia under simultaneous application of either lower body positive (LBPP, +40 mmHg), negative (LBNP, −20 mmHg) or no pressure (CON). On separate days, trials were repeated under no heat stress (NHS) and heat stress conditions of 0.6°C (MHS) and 1.2°C (HHS) increase in esophageal temperature (Tes). For all heat stress conditions, mean arterial pressure (MAP) remained greater during LBPP (p<0.001), and lower during LBNP (p<0.001) relative to CON during ischemia. Despite differences in baroreceptor loading status, no difference in LSR or CVC were observed under NS and MHS. However, during HHS, LBNP significantly reduced CVC by 16% (p=0.028) and LSR by 7% (p=0.036) relative to CON. In contrast, LBPP significantly elevated CVC by 23% relative to CON (p=0.013), albeit no differences in LSR were observed (p=0.909). These data suggest that baroreceptor loading status can modulate metaboreceptor-mediated changes in local heat loss responses but only under elevated levels of thermal stress (Tes ≥ 1.2°C). Support: Natural Sciences and Engineering Research Council (Dr. G. Kenny)