Exercise in the Heat: Implications on Kidney Function and Acute Kidney Injury

The overall purpose of this dissertation project was to explore the mechanisms underlying the risk of acute kidney injury (AKI) following exercise in the heat. The first two experiments of this dissertation revealed that Doppler ultrasound measures of renal and segmental artery hemodynamics have excellent agreement using the standard approach (i.e., measurements of three cardiac cycles) and that increases in renal vascular resistance to non-exercise sympathetic activation were abolished with passive heating and restored following cooling recovery. After exploring the utility of using the Doppler ultrasound technique in this context, a series of studies were performed to investigate the AKI biomarker response to assess the risk of AKI in humans following exercise in the heat. The findings from the third experiment of this dissertation revealed that soft drink consumption exacerbated increases in AKI biomarkers which occurred with increases in serum copeptin and serum uric acid. Next, the fourth dissertation study demonstrated that the greatest magnitudes of hyperthermia and dehydration (i.e., during the nonintervention control trial) elicited the greatest increases in the AKI biomarkers and were interpreted as the risk of AKI being attenuated when attenuating hyperthermia, dehydration, and/or both during the exercise protocol. The final study revealed that high-fructose corn syrup-sweetened soft drink (HFCS) consumption increases vascular resistance in the kidney at rest and augments increases in segmental artery vascular resistance during the cold pressor test. Notably, these findings only occurred in the HFCS trial and were not observed when consuming an equal volume of a taste and caffeine-matched sucrose-sweetened and artificially-sweetened soft drink. Thus, these data provide evidence in humans that the fructose content of the beverage has direct physiological effects on the kidney. In summary, this dissertation produced many novel findings in human subjects that further our understanding of the risk of AKI following exercise in the heat