Protein-enriched diet increases water absorption via the aquaporin-2 water channels in healthy humans

Background. According to animal experiments, a protein-enriched diet increased renal absorption of sodium and water. We wanted to test the hypothesis that a protein-enriched diet would increase the expression of the aquaporin-2 water channels and the epithelial sodium channels in the distal part of...

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Published in:Nephrology, dialysis, transplantation dialysis, transplantation, 2010-08, Vol.25 (8), p.2502-2510
Main Authors: Lauridsen, Thomas Guldager, Vase, Henrik, Starklint, Jørn, Bech, Jesper N., Pedersen, Erling B.
Format: Article
Language:English
Subjects:
Absorption - drug effects
Adolescent
Adult
Aged
aldosterone
Aldosterone - blood
angiotensin II
Angiotensin II - blood
Aquaporin 2 - metabolism
Atrial Natriuretic Factor - blood
Blood Pressure - drug effects
Cross-Over Studies
Cyclic AMP - urine
Dietary Proteins - pharmacology
Dinoprostone - urine
epithelial sodium channels
Epithelial Sodium Channels - metabolism
Female
free water clearance
Heart Rate - drug effects
Humans
Male
Middle Aged
Natriuretic Peptide, Brain - blood
Nephrons - drug effects
Nephrons - metabolism
Renin - blood
Sodium - urine
vasopressin
Vasopressins - blood
Water - metabolism
Young Adult
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Summary:Background. According to animal experiments, a protein-enriched diet increased renal absorption of sodium and water. We wanted to test the hypothesis that a protein-enriched diet would increase the expression of the aquaporin-2 water channels and the epithelial sodium channels in the distal part of the nephron using biomarkers for the activity of the two channels. Methods. We performed a randomized, placebo controlled crossover study in 13 healthy humans to examine the effect of a protein-enriched diet on renal handling of water and sodium during baseline condition and during hypertonic saline infusion. We measured the effect of the protein-enriched diet on urinary excretions of aquaporin-2 (u-AQP2), the β-fraction of the epithelial sodium channels (u-ENaCβ), free water clearance (CH2O), fractional excretion of sodium and vasoactive hormones. Results. During baseline conditions, u-AQP2 increased, and CH2O decreased during the protein-enriched diet, whereas u-ENaCβ was unchanged, although the urinary sodium excretion increased. During hypertonic saline infusion, the response in the effect variables did not deviate between protein-enriched and normal diet. Plasma concentrations of angiotensin II and aldosterone increased as well as pulse rate. Vasopressin in plasma was unchanged, and prostaglandin E2 fell during the protein-enriched diet. Conclusions. The protein-enriched diet increased water absorption via an increased transport via the aquaporin-2 water channels. The increased u-AQP2 might be due to a reduced prostaglandin level. The increase in renal sodium excretion seems to be mediated in another part of the nephron than the epithelial sodium channels.
ISSN:0931-0509
1460-2385
DOI:10.1093/ndt/gfq111