Hydration as a modulator of renal vascular control during physical work in the heat
Authors: Tourula Erica , Hess Hayden , Hite M. Jo , Hostler David , Johnson Blair , Schlader Zachary 
Published: May 2023

Occupational heat stress increases the risk of developing kidney injury (KI), which is due to the development of hyperthermia and/or hypohydration. It is speculated that this KI is caused by a relative mismatch in oxygen supply (i.e., reductions in renal perfusion) and demand (due to increased sodium reabsorption) in the renal tubules. That said, the modulatory role of hydration on renal vascular control during physical work in the heat is largely unknown. Recent observations indicate that ad lib drinking largely prevents hypohydration during simulated occupational heat stress. Thus, we tested the hypothesis that, compared to ad libitum drinking, fluid restriction induces a pro-vasoconstrictor state in the renal vasculature during physical work in the heat.On two occasions, six healthy adults (1 woman) completed 2 h of exercise in a wet bulb globe temperature of 30±0°C, conditions that are commonly experienced by U.S. outdoor workers. Exercise consisted of completing eight circuits involving treadmill walking (10 min) and rowing (5 min) at a workload eliciting an oxygen uptake of 1.2 L/min, the work intensity observed during agriculture work. In the drinking trial (Drink), subjects were provided 237 mL of sport drink every 15 min and drank ad libitum, which is compliant with workplace hydration recommendations. In the fluid restriction trial (NoDrink), no fluid was provided. Rectal temperature and body mass loss were recorded in each trial. Blood pressure and right renal segmental blood velocity (BV, Doppler ultrasound) was measured before, and following 60 and 120 min of exercise. Before and following exercise, a cold pressor test (CPT) was used to assess the renal vasoconstrictor response to sympathetic activation by immersing the subject’s foot in an agitated ice slurry for 2 min. Blood pressure and segmental BV were measured during each minute of the CPT. Segmental artery vascular resistance (VR) was calculated as mean arterial pressure divided by segmental BV. Data presented as mean ± SD.Average rectal temperature was not different between Drink (37.8±0.4°C) and NoDrink (37.9±0.4°C, p=0.517). Body mass loss was greater in NoDrink (3.1±0.7%) vs. Drink (1.8±0.8%, p=0.014). Segmental BV did not change differently between trials (interaction: p=0.651). Segmental VR did not differ between trials before (Drink: 2.7±0.6, NoDrink: 2.5±0.6 mmHg/cm/s) or after 60 (Drink: 2.8±0.7, NoDrink: 2.6±0.6 mmHg/cm/s) and 90 (Drink: 2.5±0.3, NoDrink: 2.3±0.8 mmHg/cm/s) min of exercise (interaction: p=0.988). Peak increases in segmental VR during the CPT did not differ between trials before (Drink: 0.5 ± 0.7, NoDrink: 0.9 ± 0.6 mmHg/cm/s) or after (Drink: 0.4 ± 0.7, NoDrink: 0.4 ± 0.6 mmHg/cm/s) exercise (interaction: p=0.405).These findings preliminarily indicate that fluid replacement does not modify renal vascular control during physical work in the heat. NCT: NCT05458843. Supported by: R01OH011528 This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.