Patients with chronic kidney disease (CKD) have a defect in the tubular reabsorption of sodium, and therefore the ability to excrete a sodium load is diminished compared to healthy subjects.

Urinary biomarkers reflects the water- and sodium-channel activity in the kidney and may be measured after an infusion with hypertonic saline in CKD patients and healthy subjects.

The fractional sodium excretion is elevated as high as 10-20% In patients with chronic kidney disease (CKD) Changes in the sodium intake results in a slower expansion and/or reduction in extracellular fluid in CKD patients.

Urinary biomarkers reflects the kidneys transport of sodium and water in the nephron.

Changes in the sodium-and water channel activity is induced by intervention with hypertonic Saline (3.0%) The change in sodium-and water channel activity is followed by change in extracellular and intracellular fluid compartments and the plasma concentration of vasoactive hormones.

The purpose of this study is to investigate the changes in urinary biomarkers (u-NKCC2, u-ENaC-gamma and u-AQP2), the activity of the sodium-and water channels, the extra- and intracellular fluid compartments and the plasma concentration of Vasoactive hormones in patients with CKD and in healthy subjects.

Subjects and patients are examined during one examination day. Four days prior to the examination day the subjects consume a standardized diet based on the amount of sodium and calories. On the examination day the subjects receive an infusion with hypertonic saline.

Renal function is measured by renal clearance of 51Cr-EDTA. Urinary biomarkers (u-NKCC2, u-ENaC-gamma and u-AQP2) are measured to evaluate the activity of sodium channels in the nephron and changes in fluid compartments are measured by body composition monitor.

Inclusion Criteria:

1. healthy subjects

   • healthy males and females
   • age 18-70
   • BMI range 18,5-30,0 kg/m2

2. Patients with CKD

   • age 18-70
   • eGFR 15-60 ml/min
   • BMI range 18.5 - 30.0 kg/m2

Exclusion Criteria:

1. healthy subjects

   • hypertension (ie ambulatory BP >130 mmHg systolic or/and >80 mmHg diastolic)
   • history or clinical significant signs of heart, lung, liver, kidney, endocrine, brain or neoplastic disease.
   • alcohol abuse
   • drug abuse
   • smoking
   • pregnancy or nursing
   • blood donation within a month prior to examination
   • Medical treatment apart from oral contraception

2. Patients with chronic kidney disease

   • clinical significant signs of heart, lung, liver, endocrine, brain or neoplastic disease.
   • diabetes
   • immunosuppressive medications
   • smoking
   • alcohol abuse
   • drug abuse
   • pregnancy or nursing