Acute Beetroot Juice Ingestion Does Not Alter Renal Hemodynamics during Normoxia and Mild Hypercapnia in Healthy Young Adults

Hypohydration attenuates increases in creatinine clearance to oral protein loading and the renal hemodynamic response to exercise pressor reflex

Insufficient hydration is prevalent among free living adults. This study investigated whether hypohydration alters 1) renal functional reserve, 2) the renal hemodynamic response to the exercise pressor reflex, and 3) urine-concentrating ability during oral protein loading. In a block-randomized crossover design, 22 healthy young adults (11 females and 11 males) underwent 24-h fluid deprivation (Hypohydrated) or 24-h normal fluid consumption (Euhydrated). Renal functional reserve was assessed by oral protein loading. Renal hemodynamics during the exercise pressor reflex were assessed via Doppler ultrasound. Urine-concentrating ability was assessed via free water clearance. Creatinine clearance did not differ at 150 min postprotein consumption between conditions [Hypohydrated: 246 mL/min, 95% confidence interval (CI): 212-280; Euhydrated: 231 mL/min, 95% CI: 196-265, P = 0.2691] despite an elevated baseline in Hypohydrated (261 mL/min, 95% CI: 218-303 vs. 143 mL/min, 95% CI: 118-168, P < 0.0001). Renal artery vascular resistance was not different at baseline (P = 0.9290), but increases were attenuated in Hypohydrated versus Euhydrated at the end of handgrip (0.5 mmHg/cm/s, 95% CI: 0.4-0.7 vs. 0.8 mmHg/cm/s 95% CI: 0.6-1.1, P = 0.0203) and end occlusion (0.2 mmHg/cm/s, 95% CI: 0.1-0.3 vs. 0.4 mmHg/cm/s 95% CI: 0.3-0.6, P = 0.0127). There were no differences between conditions in free water clearance at 150 min postprotein (P = 0.3489). These data indicate that hypohydration 1) engages renal functional reserve and attenuates the ability to further increase creatinine clearance, 2) attenuates increases in renal artery vascular resistance to the exercise pressor reflex, and 3) does not further enhance nor impair urine-concentrating ability during oral protein loading.NEW & NOTEWORTHY Insufficient hydration is prevalent among free living adults. This study found that hypohydration induced by 24-h fluid deprivation engaged renal functional reserve and that oral protein loading did not further increase creatinine clearance. Hypohydration also attenuated the ability to increase renal vascular resistance during the exercise pressor reflex. In addition, hypohydration neither enhanced nor impaired urine-concentrating ability during oral protein loading. These data support the importance of mitigating hypohydration in free living adults.

Acute kidney injury biomarkers and hydration assessments following prolonged mild hypohydration in healthy young adults

The high prevalence of inadequate hydration (e.g., hypohydration and underhydration) is concerning given that extreme heat increases excess hospitalizations for fluid/electrolyte disorders and acute kidney injury (AKI). Inadequate hydration may also be related to renal and cardiometabolic disease development. This study tested the hypothesis that prolonged mild hypohydration increases the urinary AKI biomarker product of insulin-like growth factor-binding protein 7 and tissue inhibitor of metalloproteinase-2 ([IGFBP7·TIMP-2]) compared with euhydration. In addition, we determined the diagnostic accuracy and optimal cutoffs of hydration assessments for discriminating positive AKI risk ([IGFBP·TIMP-2] >0.3 (ng/mL)2/1,000). In a block-randomized crossover design, 22 healthy young adults (11 females and 11 males) completed 24 h of fluid deprivation (hypohydrated group) or 24 h of normal fluid consumption (euhydrated group) separated by ≥72 h. Urinary [IGFBP7·TIMP-2] and other AKI biomarkers were measured following the 24-h protocols. Diagnostic accuracy was assessed via receiver operating characteristic curve analysis. Urinary [IGFBP7·TIMP-2] [1.9 (95% confidence interval: 1.0-2.8) vs. 0.2 (95% confidence interval: 0.1-0.3) (ng/mL)2/1,000, P = 0.0011] was markedly increased in hypohydrated versus euhydrated groups. Urine osmolality (area under the curve: 0.91, P < 0.0001) and urine specific gravity (area under the curve: 0.89, P < 0.0001) had the highest overall performance for discriminating positive AKI risk. Optimal cutoffs with a positive likelihood ratio of 11.8 for both urine osmolality and specific gravity were 952 mosmol/kgH2O and 1.025 arbitrary units. In conclusion, prolonged mild hypohydration increased urinary [IGFBP7·TIMP-2] in males and females. Urinary [IGFBP7·TIMP-2] corrected to urine concentration was elevated in males only. Urine osmolality and urine specific gravity may have clinical utility for discriminating positive AKI risk following prolonged mild hypohydration.NEW & NOTEWORTHY This study found that prolonged mild hypohydration in healthy young adults increased the Food and Drug Administration approved acute kidney injury (AKI) biomarker urinary insulin-like growth factor-binding protein 7 and tissue inhibitor of metalloproteinase-2 [IGFBP7·TIMP-2]. Urine osmolality and specific gravity demonstrated an excellent ability to discriminate positive AKI risk. These findings emphasize the importance of hydration in protecting renal health and lend early support for hydration assessment as an accessible tool to assess AKI risk.

Acute beetroot juice consumption does not alter cerebral autoregulation or cardiovagal baroreflex sensitivity during lower-body negative pressure in healthy adults

Introduction

Beetroot juice (BRJ) improves peripheral endothelial function and vascular compliance, likely due to increased nitric oxide bioavailability. It is unknown if BRJ alters cerebrovascular function and cardiovagal baroreflex control in healthy individuals.

Purpose

We tested the hypotheses that BRJ consumption improves cerebral autoregulation (CA) and cardiovagal baroreflex sensitivity (cBRS) during lower-body negative pressure (LBNP).

Methods

Thirteen healthy adults (age: 26 ± 4 years; 5 women) performed oscillatory (O-LBNP) and static LBNP (S-LBNP) before (PRE) and 3 h after consuming 500 mL of BRJ (POST). Participants inhaled 3% CO2 (21% O2, 76% N2) during a 5 min baseline and throughout LBNP to attenuate reductions in end-tidal CO2 tension (PETCO2). O-LBNP was conducted at ∼0.02 Hz for six cycles (-70 mmHg), followed by a 3-min recovery before S-LBNP (-40 mmHg) for 7 min. Beat-to-beat middle cerebral artery blood velocity (MCAv) (transcranial Doppler) and blood pressure were continuously recorded. CA was assessed using transfer function analysis to calculate coherence, gain, and phase in the very-low-frequency (VLF; 0.020-0.070 Hz) and low-frequency bands (LF; 0.07-0.20 Hz). cBRS was calculated using the sequence method. Comparisons between POST vs. PRE are reported as mean ± SD.

Results

During O-LBNP, coherence VLF was greater at POST (0.55 ± 0.06 vs. 0.46 ± 0.08; P < 0.01), but phase VLF (P = 0.17) and gain VLF (P = 0.69) were not different. Coherence LF and phase LF were not different, but gain LF was lower at POST (1.03 ± 0.20 vs. 1.12 ± 0.30 cm/s/mmHg; P = 0.05). During S-LBNP, CA was not different in the VLF or LF bands (all P > 0.10). Up-cBRS and Down-cBRS were not different during both LBNP protocols.

Conclusion

These preliminary data indicate that CA and cBRS during LBNP in healthy, young adults is largely unaffected by an acute bolus of BRJ.