| Mentha pulegium | |
|---|---|
 | |
Scientific classification | |
| Kingdom: | Plantae |
| Clade: | Tracheophytes |
| Clade: | Angiosperms |
| Clade: | Eudicots |
| Clade: | Asterids |
| Order: | Lamiales |
| Family: | Lamiaceae |
| Genus: | Mentha |
| Species: | M. pulegium |
| Binomial name | |
| Mentha pulegium | |
Mentha pulegium, commonly(European) pennyroyal, orpennyrile, also calledmosquito plant[2] andpudding grass,[3] is aspecies offlowering plant in themintfamily,Lamiaceae, native toEurope,North Africa, and theMiddle East.[4] Crushed pennyroyal leaves emit a very strong fragrance similar tospearmint. Pennyroyal is a traditionalfolk remedy,emmenagogue,abortifacient, andculinary herb, but is toxic to the liver and has caused some deaths.[5] European pennyroyal is related to an American species,Hedeoma pulegioides. Though they differ ingenera, they share similar chemical properties.[6]
An annual to perennial plant with creeping or erect branched stems to about 40 cm in height. The stems are square in cross-section and can vary from hairless on some plants to densely hairy on others, with a green to sometimes red or purplish colour. The leaves, which grow inopposite pairs, are narrowly oval, 2–3 cm long x 1 cm wide, downy, sparsely toothed towards the tip, and taper into a shortstalk. All parts of the plant are strongly scented when crushed but it does not have noticeable glands on its surface. The small (6 mm) flowers are densely packed in whorls at the nodes, widely separated, above pairs of leaf-likebracts. Thecalyx is a ribbed tube about 3 mm long, with five triangular teeth, the lower two being narrower and slightly longer than the upper three; it is hairy both on the inside and the outside. Thecorolla has four mauve lobes or "petals" and is hairy only on the outside. The flowers arebisexual and have four longstamens, two (or all four) of which project well beyond the corolla lobes. There is one longstyle which is forked to produce twostigmas, which also project from the flower. The fruits consist of a cluster of four brown, 1-seedednutlets, each about 0.7 mm long.[7]
The flowering period starts in June and continues into mid-summer,[8] although in northern countries it flowers rather later, sometimes as late as September, when it can fail to set seed.[9]
Itschromosome number is 2n = 20.[10]
The native range of pennyroyal is thought to be around the easternMediterranean, where it grows in damp meadows, around pools and in stream margins.[8] It is, however, very widely established around the world, including North and South America, throughout Africa, Asia, Australia and New Zealand. In many places it is considered a troublesome weed of agriculture.[11][12] Towards the northern edge of its range, as in Britain, it is considered to be rare and declining,[13] except where introduced.[citation needed]
The habitat of pennyroyal is seasonally damp pasture, where standing water over the winter leaves bare ground in the summer, and where livestock preferentially graze other plants. An analogue of this habitat is found on roadsides, where trampling or disturbance of the ground produces similarly bare soil, particularly where there is waterlogging in winter. It is also found along watercourses, in wet woodland and in abandoned fields.[11]
In California, where it is considered an invasive species, it occupies a similar niche, in seeps, streamsides, vernal pools and swales, marshes, and ditches. There is some speculation that it may displace native species in these areas.[14]
Few animals eat pennyroyal. In Britain, the only insect known to feed on it is the bugHeterogaster artemisiae Schilling, which is a seed bug that normally feeds onwild thyme.[15]
It is considered anaxiophyte in many British counties, because low-intensity pasture is a rare habitat, although it has been spreading in recent decades.[16] ItsEllenberg values in Britain are L = 8, F = 7, R = 5, N = 7, and S = 0.[17]
Documented use of pennyroyal dates back to ancientGreek,Roman, andMedieval cultures. Its name – although of uncertain etymology – is associated with Latinpulex (flea), alluding to the manner it was used to drive away fleas when smeared on the body.[18] Pennyroyal was commonly incorporated as a cookingherb by theGreeks andRomans. A large number of the recipes in the Roman cookbook ofApicius called for the use of pennyroyal, often along with such herbs aslovage,oregano andcoriander. Although it was commonly used for cooking also in theMiddle Ages, it gradually fell out of use as a culinary herb and is seldom used as such today.[19]
Records from Greek and Roman physicians and scholars contain information pertaining to pennyroyal's medicinal properties, as well as recipes used to prepare it.Pliny the Elder, in his encyclopediaNaturalis Historia (Natural History), described the plant as anemmenagogue, and that it also expelled a deadfetus.[20]Galen only listed pennyroyal as an emmenagogue, as didOribasius. Roman and Greek writers QuintusSerenus Sammonicus andAspasia the Physician however both agreed that pennyroyal, when served in tepid water, was an effective abortive method.[20] A medical text ongynecology attributed toCleopatra (though it was actually written by a female Greek physicianMetrodora) recommends the use of pennyroyal with wine to induce abortions.[20]
In regard to its contraceptive properties, it was referred to in a joking manner inAristophanes' playPeace (421 BCE). The godHermes provides the male character Trygaios a female companion; when Trygaios asks if there would be a problem if she became pregnant, Hermes responds, "Not if you add a dose of pennyroyal."[18] In a similar manner, in Aristophanes' comedyLysistrata, after a pregnant female character on stage is told to withhold her body sexually from her husband, a slender female character, in comparison to the pregnant woman, is described as "a very lovely land Well croppy, and trimmed and spruced with pennyroyal."[18]
Early settlers incolonial Virginia used dried pennyroyal to eradicate pests. Pennyroyal was such a popular herb that theRoyal Society published an article on its use against rattlesnakes in the first volume of itsPhilosophical Transactions in 1665.[21] 17th-century apothecary and physicianNicholas Culpeper mentions pennyroyal in his medical textThe English Physitian, published in 1652.[22] In addition to its abortive properties, Culpeper recommends its use forgastrointestinal ailments, such asconstipation andhemorrhoids, as well asitching and blemishes to the skin, and eventoothaches.[22]
Pennyroyal is an essential ingredient in the North african dish, which is still eaten to this day, calledBatata fliou [fr].
Pennyroyal continued to be used up through the 20th and 21st centuries. Its oil is still commercially available today, though little is known about the appropriate dosages for humans. Scientists therefore likely consider it unsafe for use, as it is potentially toxic.[23]
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Pennyroyal is frequently used as aninsecticide and pest repellent.[24] As a pest repellent, it is used to keep fleas away from household animals as well as on humans to ward off gnats and mosquitos. Some flea collars for pets have pennyroyal oil or the herb can be crushed in the lining. Humans have also put crushed pennyroyal stems in their pockets or on their clothing to ward off unwanted insects.[25] However, when using the pennyroyal plant as a pest repellent, the use of the concentrated pennyroyal oil should be avoided. Pennyroyal oil can be extremely toxic to both humans and animals, even in small quantities. With the use of pennyroyal around animals and humans comes the risk of it being absorbed through the skin and causing negative health effects. The less concentrated leaves of the plant should be used instead as an insect repellent.
Pennyroyal has historically also been used as a mint flavoring in herbal teas and foods. Pennyroyal tea has been used for cold relief, fevers, coughs, indigestion, liver and kidney problems and headaches.[26] The fresh or dried leaves of pennyroyal have also been used when treating influenza, abdominal cramps, to induce sweating, as well as in the treatment of diseases such as smallpox and tuberculosis.[27] To make the tea, the leaves of the plant are boiled in hot water. The lower concentrations of toxic chemicals in these teas are less harmful than pennyroyal oil. It is recommended that people only drink pennyroyal tea periodically, as it is taxing on the body and should not be drunk on a regular basis. Consumption of pennyroyal tea can be fatal to infants and children.[28]
In Italy the fresh leaves of this plant, which in Rome and the surrounding area is calledmenta romana, are used inthe capital's cuisine to flavour lamb andtripe.[29] In culinary use it should not be confused withlesser calamint (Clinopodium nepeta), which in Rome is used to prepareartichokes.
The pennyroyal plant has also been used as anemmenagogue and anabortifacient.[30] Chemicals in the pennyroyal plant cause the uterine lining to contract, causing a woman's uterine lining to shed. Women who struggle with regulating their menstrual cycle or suffer from a cystic ovary syndrome may choose to drink pennyroyal tea. Pennyroyal tea is subtle enough to induce menstrual flow with minimal risk of negative health effects. More concentrated versions of the plant, such as the oil, are much more toxic and will likely force a miscarriage if ingested by a pregnant woman.[31] Since the U.S. Congress passed the Dietary Supplement Health and Education Act in October 1994, all manufactured forms of pennyroyal in the United States have carried a warning label against its use by pregnant women, but pennyroyal is not regulated by the U.S. Food and Drug Administration.[32]
Rennie's 1833 supplement to the pharmacopeias admitted its use as an "expectorant, diuretic, and emmenagogue" in doses of 10grains to 1scruple (0.6–1.3g) of the powdered dried herb, but dismissed the use of the Pennyroyal Water (Aqua Pulegii) as "popularly but erroneously supposed" to be an abortifacient [no mention is made of toxicity].[33]
At least one study has shown pennyroyal oil to have potentacaricidal activity againsthouse dust mites.[34]
Pennyroyal is toxic to humans and has differing effects dependent on the volume and concentration ingested. The most concentrated and toxic form of the pennyroyal plant is pennyroyal oil. The oil contains 80% to 92% of cyclohexanone pulegone.Pulegone, the molecule in highest concentration in the pennyroyal plant, causes a variety of ailments in those who ingest it and is what causes the plant to have its peppermint flavor.[35]
Symptoms that may persist after ingesting a small dose (<10 mL) of pennyroyal oil are nausea, vomiting, abdominal pain and dizziness. Larger volumes may result in multiorgan failure that could lead to death. There are no current toxicokinetics studies performed on humans for the effects of pulegone, but there are some studies performed on other mammals. When pulegone is ingested, it is broken down by the liver and reacts to form multiple toxic metabolites that can wreak havoc in the body. Some identified metabolites arementhofuran, piperitenone,piperitone, andmenthone.[36]
The active chemical in pennyroyal is pulegone. Pulegone is aketone and on the cellular level, ketones can act asenzyme inhibitors. The carbonyl center of the pulegone structure acts as a strong electrophile, causing active sites on enzymes to bind with pulegone instead of the target protein.
The exocyclicdouble bond found in pulegone is vital to the activation and binding mechanism of the molecule and causes it to be an effectivehepatotoxin. When ingested, pulegone targets the liver and kidney, among other organs. Studies conducted on rats show that one of the main effects is the inhibition of contractile activity in themyometrium and death bykidney failure. The studies also found that long-term exposure to pennyroyal increased incidences of urinary bladder tumors.[36]
The exactmechanism of action by which pennyroyal inducesmenses andabortions in humans is still unknown. Studies using animal models speculate the source of liver toxicity is due to one of the many constituents the plant contains: pulegone, a monoterpene. Pulegone is metabolized bycytochrome P450 (CYP 1A2 and 2E1) and converted to several toxins.[37] Bothin vitro andin vivo studies have found the pulegone metabolitementhofuran to be an inhibitor ofCYP2A6, accounting for a significant degree of pennyroyal'shepatotoxicity.[38][39][40]
The exact pathway pulegone undergoes to be converted to menthofuran is unknown, but one study strongly suggested it included allylic oxidation of a methyl group (from CYP450), intramolecular cyclization to form a hemiketal, and subsequent dehydration to form the furan.[39] Additionally, pulegone and menthofuran may deplete glutathione levels, leaving hepatocytes vulnerable to free radical damage.[39]
There is no known antidote for pennyroyal toxicity.[30] Case studies involving pennyroyal poisonings have reported the use ofgastric lavages and administration ofemetics orvomiting inducing agents, or absorbents likeactivated charcoal.[6] Asglutathione depletion has been shown to regulate liver toxification, administration ofN-acetylcysteine in similar doses as given foracetaminophen toxicity have been given to patients.[41]
A study testing pulegone toxicity found inhibitors of cytochrome P450, such ascobaltous chloride orpiperonyl butoxide, blocked toxicity.[39] Such testing has not been expanded to humans, however, as the pennyroyal mechanism of toxicity is still not entirely understood.
{{cite book}}: CS1 maint: location missing publisher (link)
Chisholm, Hugh, ed. (1911)."Pennyroyal" .Encyclopædia Britannica (11th ed.). Cambridge University Press.