TAC1 and Headache: Graded doses of sodium nitroprusside (SNP, 0.2 to 0.8 μg.min-1.dL-1 forearm), substance P (0.2 to 0.8 pmol.min-1.dL-1 forearm) and NG-monomethyl-L-arginine (L-NMMA, 0.1 to 0.4 μmol.min-1.dL-1 forearm) were infused into the brachial artery of 16 migraine patients with or without aura during a headache-free interval and 16 age- and sex-matched subjects without a history of migraine.