Continuous Subcutaneous Administration of Miso Extracts Attenuates Salt-Induced Hypertension in Dahl Salt-Sensitive Rats

Abstract

Objective: Long-term intake of Miso attenuates hypertension in Dahl salt-sensitive (Dahl S) rats through an increased urinary sodium excretion. We examined whether a bolus injection into the peritoneal cavity (i.p.) or a continuous subcutaneous infusion of a Miso extract attenuates hypertension in Dahl S rats. Materials and Methods: We investigated the effects of a bolus, i.p. injection of 50 mg Miso extract in 0.5 mL on hypertension in Dahl S rats, and examined whether a long-term subcutaneous infusion of the Miso extract (50 mg Miso/day), using an osmotic mini-pump working for 14 days, attenuates hypertension in Dahl S rats. Results: A bolus, i.p. injection of 50 mg Miso extract decreased SBP in 2 hrs. The reduction was significant at 4 hrs, and SBP returned to the baseline at 24 hrs. The SBP reduction at 4 hrs after the injection was increasingly greater each day during the 4 days. The SBP reduction by the Miso extract was dose-dependent and the antihy-pertensive activity occurs in a <5 kDa fraction of the extract. The subcutaneous infusion of 50 mg Miso extract/day for 14 days significantly attenuated hypertension in Dahl S rats. The SBP reduction was associated with significant decreases in the heart and kidney weights. Urinary protein excretion significantly decreased in the Miso group. The SBP reduction was not associated with increases in either urinary sodium excretion or fractional excretion of sodium. Conclusions: SBP reduction by very low-dose of the Miso extract may be mediated partly by mechanisms other than renal sodium handling.