(A) Effect of Viola odorata crude extract (Vo.Cr) and (B) verapamil on baseline tension and on high K+ and phenlyephrine (PE)-induced contractions in the absence and presence of L-NAME in endothelium (E)- intact and E-denuded isolated rat aortic preparations. The responses on baseline are expressed as a percentage of PE-induced contraction. (C) The concentration-response curves of Ca++ in the absence and presence of increasing concentrations of Vo.Cr and (D) verapamil in isolated rat aortic preparations. Values shown are mean ± SEM; n = 4-7. In (A) and (B), *P < 0.05, ** P < 0.01 and *** P < 0.001 represent comparison of responses on E- intact preparations in the absence vs. presence of L-NAME (Student's t-test). In (C) and (D), *** P < 0.001 shows a comparison with control maximum (Two way ANOVA followed by Bonferroni's post-test correction).