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The Influence of Salt Loading on Glomerular Filtration Rate and Blood Pressure Variability in Healthy Young Adults
Author(s) -
Barnett Alex,
Babcock Matthew,
Watso Joseph,
Migdal Kamila,
Farqhuar William,
Robinson Austin
Publication year - 2021
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.2021.35.s1.03680
Subject(s) - renal function , medicine , creatinine , placebo , blood pressure , glomerular hyperfiltration , microalbuminuria , crossover study , urine , endocrinology , excretion , urology , kidney , pathology , diabetic nephropathy , alternative medicine
Purpose High dietary sodium (Na + ) is associated with glomerular hyperfiltration in patients with hypertension. Glomerular hyperfiltration is predictive of future cardiovascular and kidney disease. High dietary Na + is also associated with greater blood pressure variability (BPV), which is predictive of target organ damage. However, it is unclear if short‐term Na + loading influences glomerular filtration rate (GFR) and BPV in healthy young adults. Therefore, we tested the hypothesis that short‐term high Na + intake would induce glomerular hyperfiltration (GFR > 135 ml/min) and increase BPV in healthy young adults. Methods Twenty participants (12M/8F; age: 24±4 years; BMI: 23.1±0.6 kg/m 2 ; BP: 112 ±10/64±9 mmHg; mean ± SD) participated in a double‐blind, placebo‐controlled, randomized, crossover study. For 10‐days, we asked participants to consume a 2,300 mg/day Na + diet and supplement with salt (3,900 mg/day of Na + ) or placebo (dextrose) capsules. The conditions were separated by ≥ two weeks and we tested female participants during the placebo phase of oral contraception. Participants collected their urine for the final 24 hours of each supplementation period to assess Na + excretion to verify diet adherence. We measured serum creatinine (Jaffe reaction) to assess estimated GFR via the CKD‐EPI equation (along with sex, age and race), and serum/urine creatinine to measure creatinine clearance. We measured brachial (oscillometric) and beat‐to‐beat BP (photoplethysmography). We used the average real variability index and standard deviation (SD) to assess beat‐to‐beat systolic, diastolic and mean BPV. Our statistical analyses included paired t‐tests, Wilcoxon, and Chi‐squared tests. Results Compared to placebo, Na + supplementation increased urinary Na + excretion (placebo: 139.9±68.4 vs. Na + : 282±69.8 mmol/24 hours, p<0.001) without differences in mean arterial BP (placebo: 77±7 vs. Na + : 77±6 mmHg, p=0.64). Estimated GFR was not different between conditions (p=0.27). However, compared to placebo, creatinine clearance increased with Na + supplementation when unadjusted (placebo: 111±33 vs. Na + : 145±24 ml/min, p<0.001) and adjusted (placebo: 106±31 vs. Na + : 137±24 ml/min/1.73m 2 , p<0.001) for body surface area. There was a trend for an increased prevalence of glomerular hyperfiltration in the Na + condition compared to placebo when evaluating unadjusted (placebo: 6/20 [30%] vs. Na + : 12/20 [60%], p =0.057) but not adjusted creatinine clearance. There were no differences in measures of BPV except SD of systolic BP (placebo: 5.6±2.2 vs. Na + : 6.5±2.0 mmHg, p=0.035) was modestly increased with Na + supplementation. Conclusion Our preliminary data suggests that compared to CKD‐EPI, creatinine clearance is a more sensitive measure for detecting glomerular hyperfiltration with salt loading in healthy young adults. Moreover, salt loading doesn't increase BPV.