Bronchospasmolytic activity of the extract and fractions of Asystasia gangetica leaves

Abstract

Summary: The bronchospasmolytic constituent of leaves of Asystasia gangetica (L.) T. Anderson, sub-specie micrantha (Nees) Ensermu (Acanthaceae) was isolated by bio-activity-guided technique. The bronchospasmolytic effect of the fractions of the leaf extract as well as the isolate AG-1 was evaluated using histamine-induced contraction of the guinea pig trachea and pre-contracted trachea (pathological tissue). The results showed that the fractions and AG-1 inhibited contractions of the guinea pig trachea induced by histamine in a dose dependent manner. The isolated constituent, (AG-1) caused 82% inhibition of maximal contraction produced by histamine at a concentration of 400μg/ml. On histamine (8μg/ml) pre-contracted trachea, cumulative doses of the fractions evoked a dose dependent relaxation.  Phytochemical analysis showed that the isolated compound (AG-1) tested positive to terpenoids while the fractions contained typical constituents such as carbohydrates, alkaloids, saponins, steroids, flavonoids and glycosides. These findings suggest that the usefulness of leaves of A. gangetica in the treatment of asthma may derive from bronchospasmolytic effect of terpenoid compounds in the leaves.

Industrial relevance: Asthma is currently a worldwide problem, with increasing prevalence in both children and adults; a prevalence rate of 5 – 10% has been reported for Nigeria.  Drugs used in the management include bronchodilators which are short-term relievers and anti-inflammatory drugs which are long-term controllers. Despite the availability of oral and inhaled medications, the prevalence of asthma is on the rise (NHLBI/WHO 1995). The challenge of developing new effective, safe and long lasting antiasthmatic drugs from natural products appears inevitable. The leaves of Asystasia gangetica L. (T). (Acanthaceae), a traditional anti-asthma remedy, offer great potential for the development of a novel anti-asthmatic agent. The leaves have been shown to possess antihistaminic, bronchospasmolytic and anti-inflammatory properties. The aim of this research was to isolate and pharmacologically characterize the anti-asthmatic constituent of the leaves of this plant using bioactivity-guided fractionation of the leaf extract.