The vasorelaxant effect of Viscum album leaf extract is mediated by calcium-dependent mechanism.

Viscum album leaf extract has a folk reputation as an antihypertensive agent in Nigeria. Evidence suggests that it has a relaxant effect on smooth muscle. The present study was designed to investigate the role of calcium in the vasorelaxant effect of this extract. Concentration response studies to noradrenaline, KCl and CaCl2 were carried out in rat aortic rings with and without the extract in physiological salt solution (n=6 each). Also the role of intracellular calcium mobilisation was studied by measuring the phasic response to noradrenaline in Ca(2+)-free EGTA physiological salt solution (n=6). The contractile responses to noradrenaline or KCl were attenuated (P < 0.05) and shifted to the right in the presence of the extract. Also the contractile response to CaCl(2) in the presence of noradrenaline or KCl was attenuated (P < 0.05) and shifted to the right, while the phasic response to noradrenaline was significantly (P < 0.05) diminished These results suggest that the vasorelaxant effect of Viscum album extract may be mediated by a non-specific non-competitive inhibition of Ca(2+) influx as well as inhibition of Ca(2+) mobilization from intracellular stores. This implies that it may contain vasorelaxant agents that may have calcium antagonistic potential.