Greater Plantain (Plantago major) and Cough: evidence and sources

Plantago major L. leaves have been used as a wound healing remedy for centuries in almost all parts of the world and in the treatment of a number of diseases apart from wound healing. These include diseases related to the skin, respiratory organs, digestive organs, reproduction, the circulation, against cancer, for pain relief and against infections. P. major contains biologically active compounds such as polysaccharides, lipids, caffeic acid derivatives, flavonoids, iridoid glycosides and terpenoids. Alkaloids and some organic acids have also been detected. A range of biological activities has been found from plant extracts including wound healing activity, anti-inflammatory, analgesic, antioxidant, weak antibiotic, immuno modulating and antiulcerogenic activity. Some of these effects may attribute to the use of this plant in folk medicine.

Plantago major has been used widely since ancient times, to manage a wide range of diseases including constipation, coughs and wounds. The aim of this study is to review the traditional application, botanical characterization, pharmacological activities, phytochemistry effects and toxicity of Plantago major. In this review study, medicinal properties of Plantago major are collected from credible pharmacopeias, textbooks of traditional Persian medicine (TPM) belonging to the 10-18th century AD, such as "The Canon of Medicine", "Makhzan-Al- Advia" and so on. Moreover, electronic databases including Scopus, Medline and Web of science were explored for this purpose. Plantago major has been prescribed in various forms such as roasted seeds, decoction, syrup, liniment, gargle, rectal enema, vaginal suppository, eye and nasal drop for each illness by TPM scholars. Some of its traditional properties including wound healing, antipyretic, antitussive, anti-infective, anti-hemorrhagic, anti-inflammatory, diuretic, laxative, astringent and hemostatic have been confirmed in recent researches. Phytochemical investigations showed that Plantago major contains volatile compounds, triterpenoids, phenolic acids and flavonoids. Modern pharmacological studies have proven some of the traditional applications of Plantago major. Nevertheless, more investigations are required on this plant, because it has the potential to be used to produce various natural medications.

This study was conducted to evaluate the possible mechanisms of the relaxant effects of hydroalcoholic extract of Plantago major (P. major) on tracheal smooth muscle (TSM) in rats. The effects of cumulative concentrations of P. major (5, 10, 20 and 40 mg/mL) and theophylline (0.2, 0.4, 0.6 and 0.8 mM) were evaluated on pre-contracted TSM with 10 μΜ methacholine or 60 mM KCl. To determine the possible mechanisms, the relaxant effect of the plant was also examined on incubated TSM with atropine, indomethacin, chlorpheniramine, glibenclamide, diltiazem, papaverine, and propranolol. The results indicated concentration-dependent relaxant effects for P. major in non-incubated TSM contracted by methacholine or KCl. There was no statistically significant difference in the relaxant effects of P. major between non-incubated and incubated tissues with indomethacin, papaverine, and propranolol. However, the relaxant effects of P. major in incubated tissues with atropine (p<0.01 to p<0.001), chlorpheniramine (p<0.05 to p<0.001), glibenclamide (p<0.05), or diltiazem (p<0.01) were significantly lower than non-incubated TSM. P. major indicated relatively potent relaxant effects which were lower than those of theophylline. Muscarinic and histamine (H1) receptors inhibition, as well as calcium channel blocking and potassium channel opening effects are suggested to contribute to the TSM relaxant effect of the plant.