Withanolides from Whitania aristata and their diuretic activity.

AIM OF THE STUDY: Withania aristata is an endemic plant used traditionally in Canary Islands as a diuretic. In this paper, we report on this pharmacological activity in several extracts of the dry vegetal material collected and the identification and diuretic activity of two withanolides, one of them previously not reported, isolated from the most active fraction. MATERIAL AND METHODS: Four Whitania aristata extracts at 100 mg/kg were orally administered to laboratory animals to evaluate their diuretic activity. From the most active fraction, two withanolides were isolated. Both and a mixture of them at 5 and 10 mg/kg were analyzed too as diuretics. Water excretion rate and content of Na(+) and K(+) electrolytes were measured in the urine of saline-loaded animals. RESULTS: Whitania aristata water fraction, the two withanolides and the mixture of these compounds displayed high diuretic activity, with a significant excretion of sodium and potassium ions in laboratory animals. CONCLUSIONS: This research supports the ethno-medicinal use of Whitania aristata as diuretic. This activity seems to be associated to the presence of a new type of natural diuretic agents, such as withaferin A and witharistatin.

Diuretic activity of some Withania aristata Ait. fractions.

We previously reported on the significant dose-dependent diuretic effects produced in laboratory rats by hot water infusions and methanol extracts of Withania aristata Ait., where notable increases were observed in the excretion of water and sodium, with an interesting potassium-saving effect. The present study gives the results of the diuretic effects in rats of the hexane, dichloromethane, ethyl acetate, butanol and methanol-water fractions of the previously studied methanol extract. Water excretion rate, pH, density, conductivity and content of Na(+), K(+) and Cl(-) were measured in the urine of the rats when subjected to hypersaline conditions. Of the above fractions, the methanol:water extract (100mg/kg) showed the most interesting diuretic activity (25%; p<0.01), which suggested that increase in the polarity of the extracting solvent led to an increase in the concentration of the polar compounds responsible for the diuretic effect. These data, together with previous results on the aqueous and methanol extracts, reaffirm assertions made regarding the effectiveness of the extracts of this plant against urinary pathologies in the Canary Islands folk medicine.

Unambiguous 13C NMR assignment of acnistins and absolute configuration of acnistin A.

Carbon and proton atoms were fully assigned in this new type of withanolide by HMQC and HMBC experiments. The absolute configuration of acnistin A was determined by X-ray diffraction. Proton and 13C NMR measurements are particularly useful in identifying members of this group of natural products.