The influence of protease‐activated receptor 2 stimulation on cutaneous vascular and sweating responses during exercise in the heat in older males.

Stimulation of protease‐activated receptor 2 (PAR‐2), which is present on cutaneous epithelial cells and eccrine sweat glands, induces cutaneous vasodilation but not sweating in young adults during passive rest in a thermoneutral environment (~23°C). While recent data from our laboratory suggest that PAR‐2 activation does not influence these heat loss responses in young males during rest or exercise in a hot environment, it is unknown how stimulation of this receptor modulates cutaneous vasodilation and sweating in older males. Ten healthy older males (age: 61 ± 4 yrs) rested in a thermal chamber regulated to 25°C (baseline) while four microdialysis fibres were continuously perfused with 1) lactated Ringer's (Control) or the PAR‐2 receptor agonist SLIGKV‐NH 2 at concentrations of 2) 0.05 mM, 3) 0.5 mM and 4) 5 mM. Chamber temperature was then increased to 40°C and, following ~60 min of passive heat exposure, participants performed 50‐min of moderate intensity cycling (200 W·m −2 of metabolic heat production). Local forearm cutaneous vascular conductance (CVC) and sweat rate were measured continuously at each treatment site. At baseline, CVC was elevated at the 5 mM SLIGKV‐NH 2 skin site (40 ± 15%CVC max ) relative to Control (11 ± 4%CVC max ; P<0.01). By contrast, no differences were observed between treatment sites during passive exposure to 40°C (all P≥0.08) or at end‐exercise (all P≥0.22). Sweat rate was similar between treatment sites during both the baseline (all P≥0.53) and passive heat exposure (P≥0.28) periods. However, end‐exercise sweat rate was attenuated compared to Control (1.62 ± 0.30 mg·min −1 ·cm −2 ) with 0.05 mM (1.20 ± 0.29 mg·min −1 ·cm −2 ; P<0.01), 0.5 mM (1.12 ± 0.24 mg·min −1 ·cm −2 ; P<0.01) and 5 mM (1.15 ± 0.26 mg·min −1 ·cm −2 ; P=0.01) doses of SLIGKV‐NH 2 . These findings indicate that while PAR‐2 activation can cause cutaneous vasodilation during rest in thermoneutral conditions, its influence is diminished during both passive exposure and exercise in a hot environment. Further, in contrast to previous observations made in young adults, PAR‐2 activation diminished the sweating response in older males during exercise in the heat. Support or Funding Information Natural Sciences and Engineering Research Council of Canada. This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal .

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