Dipyridamole dilates large cerebral arteries concomitant to headache induction in healthy subjects

Dipyridamole is used for secondary prophylaxis in ischemic stroke and as a vasodilator agent in myocardial scintigraphy. An important side effect to a dministering dipyridamole is headache. The aim of the current study was to investigate the effects of dipyridamole on cerebral blood flow, large arter y diameter, and headache induction. Twelve healthy subjects were included i n this single-blind placebo-controlled study in which placebo (0.9% NaCl) a nd dipyridamole 0.142 mg/kg.min were administered intravenously over 4 minu tes 1 hour apart. Blood flow velocity in the middle cerebral artery (V-mca) was recorded by transcranial Doppler and regional cerebral blood flow in t he middle cerebral artery (rCBF(mcu)) was measured using single photon emis sion computed tomography and (133)Xenon-inhalation. Blood pressure, heart r ate, and pCO(2) were measured repeatedly. Headache response was scored ever y 10 minutes on a verbal scale from 0 to 10 (10 = worst). Dipyridamole caus ed a decrease in pCO(2) (P < 0.001). pCO(2) corrected rCBF(mca) was 11.7 +/ - 6.9 mL/100 g min after placebo versus 31.2 +/- 6.9 after dipyridamole (P greater than or equal to 0.05). pCO(2) corrected V-mca decreased 8.4% +/- 1 1.7 (P < 0.001) after dipyridamole, indicating a mean 5.6% +/- 6.7 (P = 0.0 05) relative increase of the arterial diameter. After dipyridamole the medi an peak headache score was 2 (range 0 to 7) compared with 0 (range 0 to 3) after placebo (P = 0,02). Dilatation of the middle cerebral artery outlaste d the headache response. In conclusion, dipyridamole causes a modest pCO(2) independent dilatation of the MCA, which is time-linked to the onset, but not to the cessation, of headache.