The exaggerated natriuresis of essential hypertension occurs independently of changes in renal medullary blood flow

Aims: In patients with essential hypertension, abnormal renal sodium handling includes exaggerated natriuresis in response to extracellular volume expansion. We tested the hypothesis that exaggerated natriuresis is associated with increases in medullary and/or cortical renal blood flow. Methods: Patients with mild essential hypertension, but no signs of end organ damage, and control subjects were studied after 4 days of dietary standardization (<60 mmol Na ⁺  day ⁻¹ ) preceded in patients by a 14-day drug washout period. On the study day, subjects received a 4-hour intravenous volume expansion with saline (2.1% of body mass). Renal medullary and cortical blood flows were measured by PET scanning using H ₂ ¹⁵ O as tracer; anatomical regions of interest were defined by contrast-enhanced CT scanning. Results: In patients, arterial blood pressure increased during volume expansion (107 ± 2-114 ± 3 mm Hg, P < 0.05) in contrast to the control group (92 ± 2-92 ± 2 mm Hg). Renal sodium excretion increased more in patients than in controls (+133 ± 31 µmol min ⁻¹ vs +61 ± 14 µmol min ⁻¹ , respectively, P < 0.05) confirming exaggerated natriuresis. During volume expansion, renal medullary blood flow did not change significantly in patients (2.8 ± 0.4-2.5 ± 0.5 mL (g tissue) ⁻¹  min ⁻¹ ) or in controls (3.2 ± 0.3-3.1 ± 0.2 mL (g tissue) ⁻¹ min ⁻¹ ). In control subjects, renal cortical blood flow fell during volume expansion (4.1 ± 0.3-3.7 ± 0.2 mL (g tissue) ⁻¹  min ⁻¹ , P < 0.05) in contrast to patients in which deviations remained insignificant. Conclusion: Exaggerated natriuresis, a hallmark of essential hypertension, is not mediated by increases in regional, renal blood flow.