The vasorelaxant effect of viscum album leaf extract is nediated by calcium-dependent mechanisms

Abstract

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 Ca2+-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 CaCl2 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 Ca2+ influx as well as inhibition of Ca2+ mobilization from intracellular stores. This implies that it may contain vasorelaxant agents that may have calcium antagonistic potential.