Inhibitory Effect of Nigella sativa on Histamine (H1) Receptors of Isolated Guinea Pig Tracheal Chains

Abstract

In a previous study, the relaxant and anticholinergic (functional antagonism) effects of Nigella sativa have been demonstrated on guinea pig tracheal chains. To elucidate the other mechanisms responsible for this relaxant effect, the inhibitory effect of this plant on histamine H 1 receptors was examined in this study. The antihistaminic effects of aqueous and macerated extracts, 5nM chlorpheniramine, and saline were tested by performing the cumulative log concentrationresponse curves of histamine induced contraction of isolated guinea pig tracheal chains incubated with three different conditions including: 1) 1.4µM indomethacin, 2) indomethacin, 1µM propranolol, and 10 nM atropine, and 3) indomethacin and propranolol (for each group n = 8). The results showed clear parallel rightward shifts in histamine-response curves obtained in the presence of macerated extract in group 1 and aqueous extract in group 2 experiments compared with the curves obtained in the presence of saline. The EC 50 (effective concentration of histamine causing 50% of maximum response) obtained in the presence of extracts, and chlorpheniramine in all three sets of experiments were significantly higher than that of saline (P < 0.05 to p = 0.002), but maximum response to histamine obtained in the presence of extracts were lower (P < 0.01 to P < 0.001). However, the maximum response obtained in the presence of aqueous extract in group 2 experiments compared to the other two sets of experiments was improved. These results indicated a competitive antagonistic effect of Nigella sativa at histamine H 1 receptors.