Dose–response effects of one subfraction of Desmodium adscendens aqueous extract on antigen‐ and arachidonic acid‐induced contractions of guinea‐pig airways

Desmodium adscendens is used in Ghana for the management of asthma. The first fraction (F1), isolated from an aqueous extract of the plant material by flash chromatography, was evaluated for its anti‐allergic properties using ovalbumin (OA)‐ and arachidonic acid (AA)‐induced contractions of tracheal spirals and lung parenchymal strips from guinea pigs. F1 inhibited OA‐ and AA‐induced contractions in both tissues dose‐dependently. In the AA‐induced contractions, F1 was more effective on the tracheal spirals than on the lung parenchymal strip. On the OA‐induced contractions of tracheal spirals, there was enhancement of the early phase of the contraction in the absence of indomethacin. This effect, which was biphasic, was not seen when the tissues were pretreated with indomethacin. Higher concentrations of F1 were required to effect the same inhibition in the absence of indomethacin than in its presence. F1 inhibited all phases of OA‐induced contractions of lung parenchymal strips by >80% at the highest concentration used (0.9 mg/mL). The results suggest that F1 inhibits both the cyclo‐oxygenase and the lipoxygenase pathways of AA metabolism. F1 also appears to inhibit the release of arachidonic acid.