Renal cortical and medullary blood flow during modest saline loading in humans

Aim 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 H215O 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