Level of hydration and renal function in healthy humans

• Published in: Kidney international Vol. 60; no. 2; pp. 748 - 756
• Main Authors: Anastasio, Pietro, Cirillo, Massimo, Spitali, Lucia, Frangiosa, Annamaria, Pollastro, Rosa Maria, De Santo, Natale G.
• Format: Journal Article
• Language: English
• Published: New York, NY Elsevier Inc 01-08-2001; Nature Publishing; Elsevier Limited
• Subjects: Adult; Biological and medical sciences; Fasting - physiology; Female; fluid management; Fundamental and applied biological sciences. Psychology; glomerular filtration rate; Glomerular Filtration Rate - physiology; Humans; Kidney - physiology; Male; Natriuresis - physiology; osmolality; Potassium - urine; Renal Circulation - physiology; sodium; Sodium - urine; Urea - urine; urine flow; Vertebrates: urinary system; water hemodynamics; Water-Electrolyte Balance - physiology; sodium; fluid management; osmolality; urine flow; water hemodynamics; glomerular filtration rate; Human; Urine; Flow rate; Glomerular filtration; Renal function; Hydration; Osmolarity; Body weight; Natriuria; Blood plasma
• ISSN: 0085-2538; 1523-1755
• DOI: 10.1046/j.1523-1755.2001.060002748.x

Level of hydration and renal function in healthy humans.
High hydration is commonly used in renal studies to improve the completeness of urine collection. The renal effects of hydration are not well defined.
Renal function was studied under fasting conditions (baseline) and after a meat meal (2g of protein/kg body weight) in 12 healthy adults on a low and high hydration regimen of 0.5 and 4mL of oral water perkg body weight/30 min, respectively.
Urine flow, urinary and plasma Na, K, urea, and osmolality were stably different on low and high hydration regimens. At baseline, there were significant or borderline significant correlations of plasma and urine osmolality with glomerular filtration rate (GFR; inulin clearance) only in the low hydration regimen. GFR was higher in the low than the high hydration regimen at all time points. The difference was significant at baseline (19.2%) and at 90 to 180 minutes after the meal (14.4%). After the meal, GFR increased significantly over baseline values only in the high hydration regimen (30.0% at peak time). Urinary excretion of Na, urea, and osmoles was lower in the low than the high hydration regimen at all time points: The difference was significant for Na (at baseline) and osmoles (all time points). Urinary K excretion was not different in the two regimens. After the meal, there were significant increases in urinary excretion of Na (in the low hydration regimen) and urea (90 to 180min after the meal).
In fasting adults, high hydration lowered GFR and increased natriuresis. After a meat meal, GFR increased only in the high hydration regimen and natriuresis only in the low hydration regimen. Hydration affects GFR and natriuresis under fasting conditions and after a meat meal.