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.
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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