Objectives: We investigated the antihypertensive mechanism of long-term Miso soup consumption in Dahl salt-sensitive (Dahl S) rats with salt-induced hypertension.
Material and methods: Female Dahl S rats fed a low-salt (0.3% NaCl) diet were divided into three groups: (1) six rats given water, (2) six rats given 0.65% (w/v) saline solution or (3) eight rats given 5% (w/v) Miso soup containing 0.65% (w/v) saline solution. They were followed for 12 weeks. Variables in the plasma or 24-h urine were determined. Systolic blood pressure (SBP) was measured by the tail-cuff method.
Results: The SBP increased in an age-dependent manner in Dahl S rats drinking saline solutions. The elevation of SBP was significantly attenuated in Dahl S rats given Miso soup although the ultimate cumulative salt loading was much greater in the Miso group than those given the saline solutions. This SBP reduction in the Miso group was associated with an increase in fractional excretion of Na (FENa) and free water clearance in the kidney. Urinary dopamine excretions were increased in the Miso group compared with that in the saline group. The increase in urinary dopamine excretions was associated with a decrease in brain oxidative stress. Urinary dopamine excretions were an independent predictor of SBP in the Miso group.
Conclusions: Long-term consumption of Miso soup attenuated blood pressure elevation in Dahl salt-sensitive rats with salt-induced hypertension. The blood pressure reduction was due to, at least in part, constituent(s) of the Miso that increase natriuresis and diuresis and enhance dopaminergic nervous activity in the kidney.
Keywords: Dahl rats; diuresis; dopamine; miso; natriuresis; oxidative stress; salt-induced hypertension.