Abstract
3H‐ethanol and 125I‐antipyrine, freely diffusable substances that distribute in brain in proportion to blood flow, were used to indicate regional flow differences in cats with metaraminol‐induced acute hypertension. Areas with blood‐brain barrier dysfunction as indicated with Evans blue or sodium fluorescein extravasation had higher flow than non‐damaged areas suggesting a local failure of autoregulation. The results contradict the theory of vasospasm and ischaemia as the cause of permeability changes in acute hypertension but are consistent with the hypothesis that the vessels are mechanically damaged by the high intraluminal pressure.