EDN1 and Stroke: In another study, the authors used a model of endothelin-1 injection (a potent vasoconstrictor) [42] and found that the signals of hyperpolarized [1-13C]pyruvate and [1-13C]lactate were increased in the ischemic penumbra region 18 h following the induced stroke, while the [1-13C]lactate/[1-13C]pyruvate signal ratio remained unchanged.