Thirst, Plasma Copeptin, And Glomerular Filtration After Mild Dehydration In Young And Older Female Adults

PURPOSE: Aging reduces thirst and urine concentrating ability despite a preserved vasopressin response after water deprivation (WD) in males, but data on females is limited. Therefore, we tested the hypothesis that aging reduces thirst and glomerular filtration rate after WD in females. METHODS: 17 young and 9 older females (Y: 24 ± 4 vs. O: 66 ± 6 years) without overt disease completed two trials in random crossover fashion ≥1 week apart. We assessed thirst (10 cm visual analog scale) and sampled blood in the laboratory after 3 days of euhydration (CON) and after 3 days of gradually reduced water intake concluded with a 16-h WD. Urine was collected during the last 24-h of each condition. We analyzed data using two-way mixed models (condition x age group) and report differences (∆; WD-CON) as mean ± SD or median[IQR]. RESULTS: WD raised thirst (Y: ∆4 ± 3 vs. O: ∆4 ± 2 cm; condition: p < 0.001) and 24-hour urine osmolality (Y: ∆220 ± 91 vs. O: ∆233 ± 108 mOsm/kg; condition: p < 0.001) with no effect of age or interaction (p ≥ 0.96). Irrespective of condition, older adults exhibited ~10 mOsm/kg higher plasma osmolality (age: p < 0.001), which increased after WD (Y: ∆3 ± 3 vs. O: ∆3 ± 4 mOsm/kg H₂O; condition: p = 0.001) with no interaction effect (p = 0.95). WD increased plasma copeptin - a more stable surrogate marker for vasopressin - (Y: ∆2.1[6.6] vs. O: ∆2.1[6.3] pmol/L; condition: p < 0.001), with no age or interaction effect (p ≥ 0.67). There was no age, condition, or interaction effect (p ≥ 0.07 for all) for estimated glomerular filtration (Y: ∆-10 ± 32 vs. O: 4 ± 17 ml/min/1.73m2), creatinine clearance rate (Y: 12[194] vs. O: ∆-34[73] mL/min/1.73m2), or serum Cystatin C (Y: ∆-97 ± 175 vs. O: ∆-72 ± 192 ng/mL). CONCLUSIONS: In contrast to past data among males, these results suggest that female aging may not affect thirst, urine/plasma osmolality, plasma copeptin, and glomerular filtration responses to water deprivation. More data are needed to examine potential reasons for these sex differences in the age-related decline in kidney function, such as differences in thirst threshold or vasopressin concentrations. Supported by: FSU Graduate School Legacy Fellowship (CD). NIH K01HL147998 (ATR), K01HL164978 (MCB), and K01HL160772 (JCW). AHA 23CDA1037938 (JCW). FSU ISL Planning Grant (KAS & JCW).