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 administering dipyridamole is headache. The aim of the current study was to investigate the effects of dipyridamole on cerebral blood flow, large artery diameter, and headache induction. Twelve healthy subjects were included in this single-blind placebo-controlled study in which placebo (0.9% NaCl) and dipyridamole 0.142 mg/kg.min were administered intravenously over 4 minutes 1 hour apart. Blood flow velocity in the middle cerebral artery (V-mca) was recorded by transcranial Doppler and regional cerebral blood flow in the middle cerebral artery (rCBF(mcu)) was measured using single photon emission computed tomography and (133)Xenon-inhalation. Blood pressure, heart rate, and pCO(2) were measured repeatedly. Headache response was scored every 10 minutes on a verbal scale from 0 to 10 (10 = worst). Dipyridamole caused 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% +/- 11.7 (P < 0.001) after dipyridamole, indicating a mean 5.6% +/- 6.7 (P = 0.005) relative increase of the arterial diameter. After dipyridamole the median 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 outlasted 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.