Relaxation effects of Eriobotrya japonica toward tracheal smooth muscle via action mechanism on histamine-1 receptor and phosphodiesterase-5 enzyme

The Eriobotrya japonica leaves have the activity to relax the smooth muscle in the respiratory tract. However, the mechanism of action due to that activity has never been carried out. This study aims to determine the relaxation effects of E. japonica leaves extract in the isolated trachea of the guinea pigs through the inhibition of the histamine-1 (H-1) receptor and the phosphodiesterase-5 (PDE-5) enzyme. The determination of the relaxation effects was carried out by using histamine to contract smooth muscle within the tracheal tract, followed by adding cumulative concentrations of extract. Michaelis–Menten kinetics equation was used to determine the antagonist type of extract toward H-1 receptor. The understanding of mechanism of action of the extract toward PDE-5 enzyme was performed by incubating the smooth muscle using sildenafil. The percentage value of responses, originated from the relaxation effect of the extract toward the trachea was analyzed by using the t-independent test. The result showed that the extract was able to relax the smooth muscle, which was contracted by histamine, and there was a positive correlation between concentration and relaxation effect (P < 0.05; r = 0.973). The extract also antagonized the histamine as a noncompetitive antagonist. The incubation within the trachea with sildenafil demonstrated equal relaxation effect, produced by the extract. It can be concluded that E. japonica extract had relaxation effect within the isolated trachea as antagonist noncompetitive toward H-1 receptor and inhibitor of the PDE-5 enzyme.