Blood flow in the basilar and internal carotid arteries and diameters of middle meningeal, carotid, and cerebral arteries were measured using 3Tesla magnetic resonance angiography, at baseline, during infusion of nitroglycerin or placebo, and during a provoked attack, at 6 hrs after infusion, in 32 migraineurs, aged 18-55 years, in a study at Leiden University Medical Centre, the Netherlands. Migraine headache was provoked in 20/27 (74%) migraineurs who received nitroglycerin, but in none of 5 patients who received placebo. Nitroglycerin caused a transient vasodilatation of all blood vessels. Blood vessel diameters were no different during a provoked migraine attack compared to baseline, nor between headache and non-headache sides. Blood flow in the basilar and internal carotid arteries was unchanged during nitroglycerin infusion and migraine headache. 
COMMENT. Contrary to current theory of migraine mechanisms, vasodilatation of cerebral or meningeal blood vessels is not of primary importance in the pathophysiology of the migraine headache.