Serum, interstitial and sweat ATP in humans exposed to heat stress: Insights into roles of ATP in the heat loss responses

Abstract

Hyperthermia increases intravascular adenosine triphosphate (ATP) and is associated with greater hyperthermia‐induced cutaneous vasodilation. Hyperthermia may also increase skin interstitial fluid ATP thereby activating cutaneous vascular smooth muscle cells and sweat glands. We evaluated the hypothesis that whole‐body heating would increase skin interstitial fluid ATP, and this response would be associated with an increase in cutaneous vasodilation and sweating. Nineteen (8 females) young adults underwent whole‐body heating using a water‐perfusion suit to increase core temperature by ~1°C during which time cutaneous vascular conductance (CVC, ratio of laser‐Doppler blood flow to mean arterial pressure) and sweat rate (ventilated capsule technique) were measured at four forearm skin sites to minimize between‐site variations. Dialysate from the skin sites were collected via intradermal microdialysis. Heating increased serum ATP, CVC, and sweat rate (all p ≤ 0.031). However, heating did not modulate dialysate ATP (median, baseline vs. end‐heating: 2.38 vs. 2.70 nmol/ml) (p = 0.068), though the effect size was moderate (Cohen's d = 0.566). While the heating‐induced increase in CVC was not correlated with changes in serum ATP (r = 0.439, p = 0.060), we observed a negative correlation (rs = −0.555, p = 0.017) between dialysate ATP and CVC. We did not observe a significant correlation between the heating‐induced sweating and serum, dialysate, or sweat ATP (rs = 0.091 to −0.322, all p ≥ 0.222). Altogether, we showed that passive heating increases ATP in blood and possibly skin interstitial fluid, with the latter potentially blunting cutaneous vasodilation. However, ATP does not appear to modulate sweating.