Diuretic activity and toxicity of some Verbascum nigrum extracts and fractions

Verbascum nigrum L. (Scrophulariaceae) is a perennial plant used in folk medicine for the treatment of kidney diseases due to its presumable diuretic properties.

We investigated the diuretic activity and toxicity of extracts from different parts of V. nigrum and identified a group of compounds responsible for the biological effect.

Five ethanol extracts from herb, roots, flowers, leaves and stems as well as five fractions of polar compounds isolated from herb of V. nigrum were orally administrated as a single dose of 50 mg/kg to rats. Urinary excretion and electrolyte content were measured at 3 and 6 h after the treatment. The acute toxicity of the V. nigrum extracts and fractions was evaluated in mice.

All extracts, except the one prepared from the roots, showed a significant increase of the urine output within first 3 h after their administration. The extract from stems was the most active, inducing urine output of 14.6 ± 0.8 ml/kg BW versus 5.2 ± 1.4 ml/kg BW of the control. It also demonstrated saluretic activity with a natriuretic index 4.1 and a kaliuretic index 3.8. The diuretic activity was correlated with the flavonoid content in the plant organs. Flavonoid fractions demonstrated significant activity; the higher content of flavonoids (expressed as hesperidin) translated into more pronounced diuretic (35.9 ± 2.1 ml/kg BW) and saluretic effects (natriuretic index 4.5 and kaliuretic index 5.4).

The diuretic activity of traditionally used V. nigrum was validated experimentally. The pharmacological effect was attributed to flavonoids, which accumulated in aerial parts of the plant, mainly in stems.