Evaluation of the anti-asthmatic property of Asystasia gangetica leaf extracts
Introduction
Asthma is a chronic disease of the airways/respiratory system with a worldwide incidence of 155 million (Cokson, 1999), and it is a disease that does not respect the boundaries of race, age, and gender. The availability of effective medications notwithstanding, the prevalence of asthma is increasing (Rona et al., 1995, Cokson, 1999) with 5–10% rate reported for Nigeria (Chukwu et al., 2000). There are incresing demand for the use of traditional medicines in the management of asthma, and Asystasia gangetica (L) T. Adams (Family Acanthaceae) is one of such plants with acclaimed potency in asthma.
Asystasia gangetica is a straggling herb usually found among short grasses and along pathways. The leaves are green, oval-shaped with rounded base, very slightly saw-edged, and smooth (Saunders, 1958). The plant is recognized as a potential food source because the leaves have been shown to contain high amounts of proteins, amino acids, minerals, sugars, lipids, and fiber (Yeoh and Wong, 1993).
In the traditional medicine of East Africa (Kenya), Asystasia gangetica is used as an anthelmintic. The leaves are crushed, boiled in water, and the decoction drunk as a cure for intestinal worms (Kokwaro, 1976). In Nigeria, the leaves of Asystasia gangetica are claimed to be highly effective in the local treatment of asthma (personal communication, 2000). The fresh leaves are macerated in local gin for 24 h or expressed and the extract drunk.
Over 70% of Nigeria’s more than 100 million people live in rural areas where traditional medicine practice is well established and patronized. The success of the practice has continued to reveal the potential of plants as therapeutic agents. As part of our continued efforts to screen Nigerian herbal remedies for pharmacological activity (Akah et al., 1997, Okoli and Akah, 2000, Nwafor et al., 2002), and in consideration of the claimed efficacy of Asystasia gangetica in native therapy of asthma, we investigated the leaves for anti-asthmatic activity.
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Collection and preparation of plant material
Fresh leaves of Asystasia gangetica were collected in June 2000 at Orba, Enugu State, Nigeria. They were authenticated by Mr. A. Ozioko of the Department of Botany, University of Nigeria, Nsukka. A specimen of the plant (no. P02611) was deposited at the University’s Herbarium.
The collected leaves were sun-dried in open air for 7 days and reduced to coarse powder using a mortar and pestle.
Extraction of plant material
About 500 g of the dried powder was successively extracted with n-hexane, ethylacetate, and methanol using a
Guinea pig trachea
Guinea pigs of either sex (250–500 g), starved overnight but allowed free access to water, were used. The animals were killed by a blow on the head and exsanguinated. The trachea was dissected out and cut along its length on the dorsal surface. Incomplete transverse cuts were made along the segments of the cartilage to produce a zig-zag strip. The isolated trachea was mounted in a 30 ml organ bath containing Tyrode solution, maintained at 37±1 °C and gassed with air. The tissue was equilibrated
Results
Results of the toxicological studies established an i.p. LD50 of 2150 mg/kg for the methanol extract. Phytochemical analysis indicated the presence of several bioactive constituents as shown in Table 1. Solvent removal afforded percentage extractive yield of 1.14, 1.19, and 6.84% for hexane, ethylacetate, and methanol extracts, respectively.
Discussion
The extracts inhibited trachea contractions induced by histamine, serotonin, and acetylcholine. These agents are implicated in various ways in the pathogenesis of asthma. Histamine is the most implicated mediator in bronchconstriction that accompany asthma (Summers et al., 1981). Although the role of 5-HT in asthma is uncertain, it is a potent bronchoconstrictor (Barnes et al., 1998) and also increases acetylcholine release from airway nerves via 5-HT3 receptors (Takahashi et al., 1995).
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