Relaxant effects of different fractions from Nigella sativa L. on guinea pig tracheal chains and its possible mechanism(s).

The relaxant effects of four cumulative concentrations of n-hexane, dichloromethane, methanol and aqueous fractions of N. sativa (0.8, 1.2, 1.6 and 2.0 g%) in comparison with saline as negative control and four cumulative concentrations of theophylline (0.2, 0.4, 0.6 and 0.8 mM) were examined by their relaxant effects on precontracted tracheal chains of guinea pig by 60 mM KCl (group 1) and 10 microM methacholine (group 2). In group 1, all concentrations of only theophylline showed significant relaxant effects. However, in group 2, all concentrations of theophylline and methanol fraction, 1.2, 1.6 and 2.0 g% concentrations of dichloromethane and 1.2 and 2.0 g% concentrations of n-hexane fractions showed significant relaxant effects compared to that of saline. In addition, in group 1, the relaxant effect of most concentrations of all fractions except the low concentration (0.8 g%) of dichloromethane and methanol fraction were significantly less than those of theophylline. The relaxant effect of different concentrations of methanol and dichloromethane fraction and 1.2, 1.6 and 2.0 g% concentrations of n-hexane fraction were significantly greater in group 2 compared to group 1 experiments. There were significant positive correlations between the relaxant effects and concentrations for all fractions (except aqucous fraction) in group 2 and for theophylline in both groups but a negative correlation for n-hexane, dichloromethane and methanol fractions in group 1. The results showed relaxant effect of most fractions from N. sativa on tracheal chains of guinea pigs which was more potent for methanol and dichloromethane fractions.