Age and Hypertension Synergize With Dehydration to Cause Renal Frailty in Rats and Predispose Them to Intrinsic Acute Kidney Injury.

Acute kidney frailty (AKF) is a condition of increased susceptibility to acute kidney injury (AKI), an abrupt impairment of renal excretory function potentially leading to severe complications. Prevention of AKI relies on the recognition of risk factors contributing to AKF. At the population level, dehydration constitutes a predisposing factor for AKI. However, renal frailty may be context-specific, with variations among patients in the types of damage and the distinct pathological mechanisms. In this regard, we studied the combined effect of dehydration with other factors on renal homeostasis, such as increasing age and hypertension. AKF status was studied in rats bearing risk factors individually and in combination and was evaluated as the level of AKI induced by a triggering dose of cisplatin, which is known to be mildly nephrotoxic for young, healthy rats. AKI was assessed through parameters of renal function (including creatinine, urea, creatinine clearance, proteinuria, and fractional excretion of sodium) and histopathology of renal tissue specimens. The hydration status was measured by bioelectric impedance and other techniques. Water deprivation induces a dehydration state characterized by reductions in body weight and urinary flow and increases in hematocrit and plasma and urine osmolality. Bioelectric impedance showed a net loss of body water after water deprivation with no relevant changes in body mass distribution. Dehydration is not sufficient to predispose young control rats to intrinsic AKI. However, the combination of dehydration with advanced age or hypertension induces AKF evidenced by a magnified response of renal dysfunction (reduced filtration and tubular function) and tubular necrosis caused by low-dose cisplatin treatment. This study highlights the relevance of addressing AKF as a premorbid condition providing prophylactic opportunities and shows that dehydration differentially predisposes to prerenal and intrinsic AKI.