Effects of thymoquinone, the major constituent of Nigella sativa seeds, on the contractile responses of rat vas deferens

We have evaluated the effects of thymoquinone on smooth muscle contraction in the isolated rat epididymal vas deferens using tension recording technique. The contractile responses to norepinephrine (NE), KCl, and electrical field stimulation were recorded using an isometric transducer. Thymoquinone inhibited the contractile responses to exogenous NE (100muM) and KCl (80 mM) in a concentration-dependent manner. Moreover, thymoquinone reduced the amplitude of electrically-evoked contraction of vas deferens in a concentration-dependent manner. Cumulative addition concentrations of CaCl2 (0.1-10 mM) to tissue bath failed to increase the amplitude of contractile responses to electrical field stimulation in the presence of thymoquinone (80 muM). These results indicate that thymoquinone induced nonselective and concentration-dependent inhibition of contractile responses to NE, KCl, and electrical field stimulation. This action may be due to the ability of this alkaloid to interfere with the mobilization of Ca2+ required for smooth muscle contraction.