Diuretic and anti-diuretic activities of the ethanol and aqueous extracts of Alismatis rhizoma

Alismatis rhizoma or Alisma orientale (Zexie in Chinese), the dried rhizome of Alisma orientale Juzepzuk (Alismataceae), is a well-known traditional Chinese medicine and is used as an agent for diuresis and for excreting dampness in Asia and Europe. In this paper, we report the diuretic activities of the ethanol extract (EE) and the aqueous extract (AE) of A. rhizoma (AR). The EE and AE were orally administered to rats. The urinary excretion rate and pH, and electrolyte excretion were measured in the urine of saline-loaded rats. The results showed that EE could increase the urine output at 2.5, 5 and 10 mg/kg doses but decrease the urine output at 20, 40 and 80 mg/kg doses compared with the control group. The 5 and 10 mg/kg doses of EE increased the urine electrolyte excretion, but the effects on Na+/K+ values were too weak to reach statistical significance. The Na+ excretion and Cl− excretion were markedly decreased with the 20, 40 and 80 mg/kg doses of EE, but the effect on K+ excretion was notably slight. All of the tested doses of AE produced an increase in urinary excretion, but the increase did not reach statistical significance. This study identified that EE but not AE presents a notable diuretic effect, and EE had diuretic and anti-diuretic effects, which appears to be related to the sodium–chloride co-transporter in the renal distal convoluting tubule. This study demonstrated for the first time that the EE of AR has a dual effect on renal function, including promotion of diuretic activity at lower doses and inhibiting diuretic activity at higher doses, and the AR dose should be given more attention in clinical applications. This study will play a critical and guiding role in the dosing of AR as a diuretic drug in clinical applications.