The Effect Of Sodium Bicarbonate Ingestion On Acute Kidney Injury After Exercise In The Heat

In response to metabolic acidosis, compensatory mechanisms are deployed by the kidney to maintain acid-base homeostasis. However, during work in the heat kidney perfusion is reduced and the metabolic cost of acid-base balance can make the kidneys more prone to acute kidney injury (AKI) risk. Sodium bicarbonate ingestion (NaHCO3) may reduce metabolic acidosis and the risk of developing AKI. PURPOSE: To determine the effects of NaHCO3 ingestion before a prolonged bout of exercise in the heat on AKI markers and kidney function. METHOD: A randomized, cross-over, double-blinded design was conducted with 8 participants (3 females) who consumed NaHCO3 (0.2 g/kg body weight) or placebo (PLA) before 120 minutes of moderate intensity exercise (walking at ~65% of maximal heart rate) in the heat (40 °C/~20% relative humidity). Blood and urine samples were collected pre-, post-, and 1 hr post-exercise. Core temperature (Tc) was measured every three minutes. Urine osmolality (Uosm), urinary creatinine (uCr), plasma osmolality (Posm), and urine flow rate (UFR) were determined pre, post, and 1 hr post-exercise. Insulin-like growth factor binding protein 7 (IGFBP7), tissue inhibitor of metalloproteinase 2 (TIMP-2), and neutrophil gelatinase-associated lipocalin (NGAL) were measured in the urine pre and 1 hr post-exercise. RESULTS: Peak Tc was not significantly different between conditions (p = 0.112, PLA = 38.26 ± 0.22 and NaHCO3 = 38.55 ± 0.50 °C). Uosm was higher post-exercise in PLA compared to NaHCO3 (p = 0.01, 472 ± 257 vs. 362 ± 229 mOsm/kg). The decline in UFR 1 hr post-exercise was greater in PLA compared to NaHCO3 (p = 0.04, Δ 523 vs. 356 ml/hr, respectively). Urine TIMP-2 corrected for UFR was higher in PLA compared to NaHCO3 at 1 hr post (p = 0.04, 0.0287 vs. 0.0075 ng/hr, respectively). Urine IGFBP-7 was not different between conditions (p = 0.766, PLA = 26 ± 21 vs. NaHCO3 = 23.2 ± 17.3 ng/mL). IGFBP-7 × TIMP-2 corrected for UFR was lower in NaHCO3, albeit not-significantly different, compared to PLA at 1-hour post-exercise (p = 0.06, 0.221 ± 0.174 vs. 0.646 ± 0.498 ng/hr). Log NGAL was not different between conditions (p > 0.05, PLA = 1.54 ± 0.17 vs. NaHCO3 = 1.41 ± 0.11 ng/mL). CONCLUSION: NaHCO3 ingestion pre-exercise in the heat reduced some markers of AKI and prevented a decrease in UFR suggesting less stress to the kidneys.