_:b668240886 . _:b668240886 . _:b668240886 "Farlex:Farlex_Partner_Medical_Dictionary_2012"^^ . _:b668240886 "http://en.wikipedia.org/wiki/EC50"^^ . _:b668240886 . _:b668240886 . _:b668240886 "A calculated value for the concentration of a vasoconstrictor at which the energy produced by the active reduction in the diameter of a blood vessel in response to the application of the stimulus is halfway between the baseline value and the highest achievable value of such stimulus-induced contractile energy. A vasoconstrictor is any agent or condition that narrows blood vessels by constricting the smooth muscle in the vessel walls."^^ .