Vasorelaxant effect of essential oil isolated from Nigella sativa L. seeds in rat aorta: Proposed mechanism

The effect of the essential oil extracted from Nigella sativa (L.) seeds (Nigella oil) was investigated for its vasorelaxant activity on isolated rat aorta. Nigella oil at concentrations of 10-100µg/mL elicited a dose-dependent relaxation of the aorta, which was pre-contracted with noradrenaline (NA, 10-6 M) or KCl (100mM). In the presence of Nigella oil (75µg/mL, the dose response curves to increasing concentrations of NA (10-9 M to 10-4M) or KCl (10mM-100mM) were displaced downwards, indicating inhibition of the vasoconstrictive effect. This relaxation effect was independent of the presence of endothelium. In addition, the vasodilatory activity of the Nigella oil was not affected by pre-treatment of the rings with NG-nitro-L-Arginine (an inhibitor of endothelial nitric oxide synthase; 0.1mM), suggesting that the vasorelaxant effect is not mediated by nitric oxide. Furthermore, pre-treatment of the rings with Nigella oil (75µg/mL suppressed the tension increment produced by increasing external calcium concentration (0.25mM to 1.5mM). Tin conclusion, the essential oil extracted from Nigella sativa seeds produces smooth muscle relaxation, which is independent of endothelium and is not mediated by nitric oxide. The results also suggest that the vasorelaxing effect of the oil results from the blockade of both voltage-sensitive and receptor-operated calcium channels, and this may have therapeutic significance, in that Nigella oil may be useful as an antihypertensive agent in humans.