effect of nigella sativa on isolated guinea pig trachea

Background- Previous studies have demonstrated the relaxant, anticholinergic (functional antagonism) and antihistaminic effects of Nigella sativa on guinea pig tracheal chains. Mechanisms responsible for the relaxant effect of this plant on tracheal chains were examined in this study.Methods- The calcium-antagonistic effects of three increment concentrations of the aqueous extracts of Nigella sativa and the calcium channel blocker diltiazem in comparison with saline were tested by measuring the cumulative concentration response curves of CaCl2-induced contractions of isolated guinea pig tracheal chains in the presence of calcium-free Krebs-Henseleit solution and 60 mM of KCl under each experimental condition (n = 7). Results-A rightward shift in the CaCl2 response curves was obtained in the presence of two different concentrations of diltiazem (1 and 5 μM) and the aqueous extract compared to the saline control curves. The effective concentration of CaCl2 causing 50% of maximum response (EC50) in the presence of two concentrations of aqueous extract and diltiazem was significantly higher than that of saline (p < 0.05 to p < 0.02). However, the maximum response to CaCl2 obtained in the presence of the final concentrations of aqueous extract and diltiazem was lower than of saline (p < 0.05 and p < 0.005 for aqueous extract and diltiazem, respectively).Conclusion-The results suggest a calcium antagonistic effect of N. sativa in isolated tracheal chains of guinea pigs.