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Horehound Herb

Scientific name : Marrubium vulgare

Common name : Horehound, hoarhound, white horehound

Botany

Horehound is native to Europe and Asia and een naturalized to other areas, including the United 5,1 It is a perennial aromatic herb of the mint family. plant grows to a height of about three feet and has leaves covered with white, woolly hairs. Horehound s small, white flowers in dense whorls which bloom June to August.

History

The leaves and flower tops of the horehound long been used in home remedies as a bitter tonic common cold. They are now used primarily as gs in liqueurs, candies and cough drops. In addi­dant had been used for the treatment /parasites and as a diaphoretic and diuretic. A different genus, the black horehound (Ballota nigra), is a fetid.odored perennial native to the Mediterranean area that is sometimes used as an adulterant of white hore­hound,

Chemistry

The bitter principle of horehound is the Jlatile oil marrubiin, a diterpene lactone. Some research­'s believe, however, that marrubiin is an artifact, gener­ed from premarrubiin during isolation. In addition to arrubiin, horehound contains a sterol in an esterified rm that is related to compounds found in other plants of e Labiatae family, and a sesquiterpene that has two mconjugated double bonds and can be isolated from e nonsaponifiable fraction of extracts.

least six flavonoids have been isolated from the herb: )igerin, luteolin, apigerin 7-glycoside, luteolin 7-glyco­je, quercetin 3-glycoside and quercetin 3-rhamnogly­side, Two crystalline precipitates from horehound have en found to contain four additional unidentified fla­noids.3 Horehound contains normal alkanes and four les of branched alkanes: 2-methylalkanes, 3-methy­(anes, 2-(omega-1 )-dimethylalkanes and 3-(omega-9)­lethylalkanes. These molecules are in the C27-C33 ies, with odd-numbered chains predominant. Two- and methylalkanes are present in approximately equal Dortions in short-chain compounds.

related species, Marrubium alysson, five known os ides: verbascoside, leucoseptoside A, martyno­
side, forsythoside B, leucosceptoside B and a new phe­nylpropanoid glycoside, alyssonoside, were isolated.

Further constituents of horehound are essential oil made up of 0.06% mono and sesquiterpenes, 2.6% to 2.9% tannic acid, resinous substances (eg, ursolic acid), sterols (eg, beta-sitosterol), mucilaginous materials, bitter glyco­sides and pure marrubina (1 ,2,5-trimethylnaftalene).

Pharmacology

Horehound has been used tradi­tionally as an expectorant and continues to find a place in cough lozenges and cold preparations. The volatile oil has been reported to have expectorant and vasodilatory effects. Similarly, marrubiin stimulates secretion by the bronchial mucosa?

A study in rats tested the hypothesis that marrubiin stimulates bile secretion. There was no evidence of this, but marrubiin acid, prduced by saponification of mar'ru­biin, and the sodium salt of marrubiin acid did stimulate bile secretion. This effect was temporary.8 Aqueous ex­tracts of horehound are said to be serotonin-antagonists in vitro.

In a recent study using rabbits, Marribium vulgare was found to have hypoglycemic effects.lO This may be im­portant for possible use as an antidiabetic agent.

Toxicology

Marrubiin has an LD50 of 370 mg/kg when administered orally to rats.8 While marrubiin has been reported to have antiarrhythmic properties, it may also induce cardiac irregularities in larger doses.

Summary

Horehound is an aromatic herb that has been widely used in folk remedies. It is most often classified as an expectorant. The active principle of the plant is marrubiin, metabolites of which may also influ­ence bile secretion. Recently, a hypoglycemic effect has been reported. Although widely known, horehound has not been the subject of a large body of literature in the West.