Ingesting menthol in a beverage may alter the sweating response during passive heat stress, but only when the...

Consuming cold fluids during heat stress can alter sweating responses; however, it remains unclear why chemical activation of cold-sensitive transient receptor potential melastatin 8 (TRPM8) with menthol only induces a cold sensation. Animal models propose that complete cold transduction with TRPM8 chemical stimulation must be combined with physical cooling to impact thermoeffector responses. To address this, 12 participants (5 females and 7 males; 22 ± 5 yr; 79.5 ± 15.0 kg; 1.8 ± 0.1 m) conducted four passive heating protocols in random order where, within trial, they consumed 3.2 mL/kg body mass of either 1) 37°C water, 2) 1.5°C water, 3) 37°C menthol solution (0.05%), or 4) 1.5°C menthol solution (0.05%); 5 min before heating, and following a 0.5°C and 1.0°C increase in rectal temperature. Forearm sweating onset was attenuated with 1.5°C compared with 37°C (+0.16°C, P = 0.001) and delayed with menthol (+0.15°C, P = 0.03), but not at the forehead (main effect of temperature: +0.08°C, P = 0.17, menthol: +0.09°C, P = 0.17). Sudomotor thermosensitivity at the forearm and forehead was attenuated with 1.5°C compared with 37°C (-0.62 mg/cm²/min/°C, P = 0.02) but not affected by menthol (-0.11 mg/cm²/min/°C, P = 0.55). A small attenuation in forearm (-0.05 mg/cm²/min) and forehead (-0.08 mg/cm²/min) sweat rate was observed with 1.5°C combined with menthol, following a 0.5°C (P < 0.04), but not a 1.0°C (P > 0.09) rise in rectal temperature; 1.5°C water alone, nor 37°C water with or without menthol, altered sweating during passive heat stress (P ≥ 0.55). Collectively, chemical stimulation of TRPM8 within the gastrointestinal tract could alter thermoregulatory sweating, but only when paired with physical cooling, and the effect is small.NEW & NOTEWORTHY Chemical stimulation of TRPM8 channels during heat stress provides alterations in thermal perception without impacting sweating. However, evidence to date in humans has not considered the impact of fluid temperature, which may be needed to fully induce cold transduction. We provide evidence that coadministration of a TRPM8 agonist with physical cold stimulation is required to alter sudomotor output during heat stress; however, this effect is small.