title: Renal cortical and medullary blood flow during modest saline loading in humans.
abstract: OBJECTIVE
  Renal medullary blood flow (RMBF) is considered an important element of sodium homeostasis, but the experimental evidence is incongruent. Studies in anaesthetized animals generally support the concept in contrast to measurements in conscious animals. We hypothesized that saline-induced natriuresis is associated with changes in RMBF in humans.
  
  
  METHODS
  After 4 days of low-sodium diet, healthy men were subjected to slow intravenous saline loading (12 μmol kg(-1) min(-1)) for 4 h. Renal medullary and cortical blood flow was determined by positron emission tomography with H(2)(15)O before and after saline infusion using two independent imaging processing methods. One based on a previously published algorithm (voxel peeling) and a novel method based on contrast-enhanced computed tomography (CT). Blood pressure was measured oscillometrically every 10 min. Cardiac output, heart rate and total peripheral resistance were recorded continuously.
  
  
  RESULTS
  Saline loading increased the urinary sodium excretion by 3.6-fold (21-76 μmol min(-1) , P < 0.01). The RMBF was 2.6 ± 0.2 mL g(-1) tissue min(-1) before and 2.7 ± 0.1 mL g(-1) tissue min(-1) after saline (n.s.). Cortical blood flow was 3.6 ± 0.1 before and 3.4 ± 0.2 after saline (n.s.). Mean arterial blood pressure did not change measurably (90 vs. 90 mmHg). Bland-Altman analysis suggested agreement between results obtained with voxel peeling (2.6 ± 0.2 mL g(-1) tissue min(-1)) and contrast-enhanced CT (2.0 ± 0.1 mL g(-1) tissue min(-1)).
  
  
  CONCLUSIONS
  In normal humans, changes in RMBF are not necessarily involved in the natriuretic response to modest saline loading. This result is in line with data from conscious rodents.
authors.affiliation: Institute of Molecular Medicine, University of Southern Denmark, Odense, Denmark.
authors.forename: M
authors.initials: M
authors.lastname: Damkjær
authors.forename: M
authors.initials: M
authors.lastname: Vafaee
authors.forename: P E
authors.initials: PE
authors.lastname: Braad
authors.forename: H
authors.initials: H
authors.lastname: Petersen
authors.forename: P F
authors.initials: PF
authors.lastname: Høilund-Carlsen
authors.forename: P
authors.initials: P
authors.lastname: Bie
mesh_terms: D001794:Blood Pressure / Q000187:drug effects; D006439:Hemodynamics / Q000502:physiology; D006801:Humans; D007668:Kidney / Q000098:blood supply* / Q000502:physiology*; D008297:Male; D009638:Norepinephrine / Q000097:blood; D010104:Oxygen Radioisotopes; D049268:Positron-Emission Tomography; D012079:Renal Circulation / Q000502:physiology*; D012083:Renin / Q000097:blood; D012965:Sodium Chloride / Q000494:pharmacology*; D014867:Water / Q000737:chemistry / Q000502:physiology; D055815:Young Adult
chemical_list: D010104:Oxygen Radioisotopes; D014867:Water; D012965:Sodium Chloride; D012083:Renin; D009638:Norepinephrine