Heat Acclimation Alters the Relation Between Hyperthermia and Biomarkers of Kidney Function During Exercise Heat Stress

Strenuous physical work in hot environments can impair kidney function and potentially cause acute kidney injury (AKI). Heat acclimation is recommended to reduce thermal strain but its efficacy in mitigating decrements in kidney function remains unclear. The present study tested the hypothesis that 10 days of heat acclimation attenuates increases in serum creatinine (ΔCr) during exercise heat stress. Twenty healthy adults (14 females) completed 10 days of fixed-intensity treadmill walking for 120 min in a climatic chamber (40°C) to induce heat acclimation. Kidney function was assessed as ΔCr from pre-to-post exercise on days 1 (D1) and 10 (D10). Plasma neutrophil gelatinase-associated lipocalin (ΔNGAL) was measured to estimate the magnitude of renal ischemia. The increase in core temperature (Tc) from pre- to post-exercise was attenuated on D10 (Post: 38.3±0.4°C) compared to D1 (Post: 38.8±0.5°C, p<0.001). Heat acclimation did not alter the increase in ΔCr and ΔNGAL to exercise heat stress ( p≥0.325). There was a strong correlation between ΔTc and ΔCr on D10 (r=0.61) but no correlation on D1 ( p=0.908). There was no correlation between ΔTc and ΔNGAL on either day ( p≥0.480). There was a strong correlation between ΔNGAL and ΔCr on D1 (r=0.694) but no correlation on D10 ( p=0.118). These findings indicate that heat acclimation does not alter the magnitude of increase in circulating biomarkers of kidney function following exercise heat stress. However, that ΔCr was correlated with ΔTc on D10 but not D1 suggests that the kidneys may exhibit increased sensitivity to hyperthermia in heat acclimated individuals.