Impact of passive heat acclimation on markers of kidney function during heat stress.

Ravanelli, Nicholas; Barry, Hadiatou; Schlader, Zachary J; Gagnon, Daniel

NEW FINDINGS What is the central question of this study? Does passive heat acclimation alter glomerular filtration rate and urine concentrating ability in response to passive heat stress? What is the main finding and its importance? Glomerular filtration rate remained unchanged following passive heat stress, and heat acclimation did not alter this response. However, heat acclimation mitigated the reduction in urine concentrating ability and reduced the incidence of albuminuria in young healthy adults following passive heat stress. Collectively, these results suggest that passive heat acclimation may improve structural integrity and reduce glomerular permeability during passive heat stress. ABSTRACT Little is known about the effect of heat acclimation on kidney function during heat stress. The purpose of this study was to determine the impact of passive heat stress and subsequent passive heat acclimation on markers of kidney function. Twelve healthy adults (7 males/5 females; 26 ± 5 y; 72.7 ± 8.6 kg; 172.4 ± 7.5 cm) underwent passive heat stress before and after a 7-day controlled hyperthermia heat acclimation protocol. The impact of passive heat exposure on urine and serum markers of kidney function was evaluated before and after heat acclimation. Glomerular filtration rate, determined from creatinine clearance, was unchanged with passive heat stress before (pre: 133 ± 41 mL/min; post: 127 ± 51 mL/min, P = 0.99) and after (pre: 129 ± 46 mL/min; post: 130 ± 36 mL/min, P = 0.99) heat acclimation. The urine-to-serum osmolality ratio was reduced following passive heating (P < 0.01), but heat acclimation did not alter this response. In comparison to baseline, free water clearance was greater following passive heating before (pre: -0.86 ± 0.67 mL/min, post: 0.40 ± 1.01 mL/min, P < 0.01) but not after (pre: -0.16 ± 0.57 mL/min, post: 0.76 ± 1.2 mL/min, P = 0.11) heat acclimation. Further, passive heating increased the fractional excretion rate of potassium (P < 0.03) but not sodium (P = 0.13) or chloride (P = 0.20). Lastly, heat acclimation reduced the fractional incidence of albuminuria following passive heating (before: 58 ± 51%, after: 8 ± 29%, P = 0.03). Collectively, these results demonstrate that passive heat stress does not alter glomerular filtration rate. However, heat acclimation may improve urine concentrating ability and filtration within the glomerulus. This article is protected by copyright. All rights reserved.