Lobelia

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Chapter: Pharmacognosy and Phytochemistry : Drugs Containing Alkaloids

Lobelia consists of the dried aerial parts of Lobelia inflata Linn, belonging to family Lobeliaceae.


LOBELIA

 

 

Synonyms

 

Herba lobellae, Indian tobacco, Pukeweed, Asthma Weed.

 

 

Biological Source

 

Lobelia consists of the dried aerial parts of Lobelia inflata Linn, belonging to family Lobeliaceae.

 

Geographical Source

 

Indigenous to Eastern and Central United States, Canada and India.

 

Cultivation and Collection

 

It is an erect annual or biennial herb, 1–2 feet high; lower leaves and also flower are stalked, the latter being pale violet-blue in colour, tinted pale yellow within. Drug is obtained both from cultivated and wild plants. It is propagated using seeds. For cultivation seeds are sown in rich, moist, loamy soil usually in March to April. After sowing, seeds are covered with soil and pressure is applied on them by placing wooden board over them and walking on it. Collection is done in August to September when capsular fruits get inflated. Aerial parts are collected and dried in the shade to maintain green colour.

 

Characteristics

 

Stem is green with purple patches. Upper part of the stem is cylindrical, hairy and having two to three wings. In the lower part it is channeled and neatly glabrous. Leaves are sessile in the upper part and prolate below. Those on the upper part of the stem are small and about 2 cm long. They are ovate, oblong and irregularly toothed. Pedicel of the flower is 3–5 mm long. Flowers are 7 mm long, light blue, having inferior ovary. Calyx consists of five subulate sepals. Corolla is tubular and bilabiate. Stamens are five, epigynous and syngenesious. At the apex of the stamen is tuft of hairs. Fruit, is an inferior capsule, 7–8 mm long, and yellowish green in colour and inflated. Capsule is obovate, bilocular and contains about 500 extremely small seeds. Pericarp is thin, membranous and bears 10 ridges. Ridges are joined by horizontal veinlets. Seeds are 0.6–0.7 mm long and 0.25–0.30 mm broad, reddish brown in colour and covered on the outer surface with fine elongated, polygonal, lignified reticulations. It has an irritating odour and taste is unpleasant, acrid and burning.

 


                                       Lobelia inflata 


Microscopy

 

The epidermis consists of axially elongated cells. Trichomes which are 1,200 μ long are present on the epidermis and stomata are parallel to the axis. The cortex region has paren-chyma which is round in shape. It has a well developed endodermis composed of large cells. The phloem has a cylindrical net work of lacticiferous vessels. It has a large pith taking about one-third to one-half of the diameter of the stern. It has thin walled parenchyma with simple pits which are lignified. In the mesophyll region of the leaf it has the elongated palisade parenchyma cells under the upper epidermis giving it a dorsiventral leaf structure. The epidermis is nearly straight anticlinal walls with thick and striated cuticle. The lower epidermis has abundant stomata. In the midrib region phloem is present which has a well developed laticiferous tissues system. It usually has uni-cellular and occasionally uni-seriate and bicellular conical trichomes which are lignified.

 

Chemical Constituents

 

Lobelia contains about 0.4% crystalline alkaloids of which lobeline is the important active alkaloid. Other alkaloids are lobelidine, lobelanidine, lobelanine and isolobinine chemically related to lobeline. Also, gum, resin, chlorophyll, fixed oil, lignin, salts of lime and potassium with ferric oxide are present. Lobelacrine, formerly considered to be the acrid principle, is probably lobelate of lobeline. The seeds contain a much higher percentage of lobeline than the rest of the plant.



Uses

 

It is mainly used as expectorant, diaphoretic, antiasthmatic. It should not be employed as an emetic. Some authorities attach great value to it as an expectorant in bronchitis, others as a valuable counterirritant when combined with other ingredients in ointment form. It is sometimes given in convulsive and inflammatory disorders, such as epilepsy, tetanus, diphtheria and tonsillitis. Lobeline is a respiratory stimulant and is used in asphyxia of the newborn, in gas, alcohol and narcotic poisoning and in drowning in water, electric shock and collapse. It has relaxant and dilatory action and is used in asthma and dyspnoea. Lobelia is also used to discontinue smoking habit. Externally, an infusion has been found useful in ophthalmia, and the tincture can be used as a local application for sprains, bruises, or skin diseases, alone, or in powder combined with an equal part of slippery elm bark and weak lye water in a poultice. The oil of Lobelia is valuable in tetanus.

 

 

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