Effect of Desmodium adscendens fraction F1 (DAF1) on tone and agonist‐induced contractions of guinea pig airway smooth muscle

Cumulative concentration‐response curves (CCRC) of histamine, carbachol and leukotriene D, (LTD 4 ), and relaxation curves were used to evaluate the nature of the modulation of allergic airway smooth muscle contraction of Desmodium adrcendens fraction F1 (DAF1). DAM significantly increased the maximal contractions ( E max ) of tracheal spirals for all three agonists, and significantly increased the pD, values for histamine and carbachol, but decreased that for LTD 4 . On lung parenchymal strips DAM had no significant effect on the shape of the CCRC, the pD, value or E max for histamine and carbachol. A significant decrease in the pD, value for LTD 4 , was observed at DAM concentrations of 0.3 and 0.9mg/mL. At the higher concentration, the decrease was accompanied by an equally significant decrease in the E max . DAF1 per se , caused relaxation of tracheal spirals. The results indicate that DAF1's effect includes a reduction in sensitivity and responsiveness to LTD 4 ‐induced contractions.