Hypohydration Attenuates Increases in Creatinine Clearance to Oral Protein Loading and the Renal Hemodynamic Response to Exercise Pressor Reflex.

Insufficient hydration is prevalent amongst 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 post-protein consumption between conditions (Hypohydrated: 246 ml/min, 95% 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 vs. 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 post-protein (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.