['In previous studies, the bronchodilator and antitussive effects of Nigella sativa have been demonstrated on guinea pigs.', 'In the present study, the effect of the hydroethanolic extract of N. sativa on tracheal responsiveness in guinea pigs exposed to cigarette smoke was examined.', 'Three groups of guinea pig models of COPD were given drinking water alone (COPD group), drinking water containing vitamin C (COPD + VC group), and N. sativa (COPD + NS group). Tracheal responses to methacholine were measured as effective concentration causing 50% of maximum response (EC50 M) in control animals (group C) and three groups of guinea pigs with COPD (n = 7, for all groups). Tracheal responses to 0.1% ovalbumin in comparison to contraction obtained by 10 µM methacholine were also examined.', 'The tracheal responsiveness to both methacholine and ovalbumin in guinea pigs with COPD were significantly higher than those of controls (P < 0.001 for both cases). The tracheal responsiveness in the COPD + VC and the COPD + NS groups to both methacholine and ovalbumin were significantly decreased in comparison to the COPD group (P < 0.05 and P < 0.001, respectively).'] Does nigella sativa Pretreatment in Guinea Pigs Exposed to Cigarette Smoke modulate In Vitro Tracheal Responsiveness?