To investigate the vasoconstrictor effect of 5-hydroxytryptamine (5-HT 1B/1D ) receptor agonists for
migraine treatment, changes in cerebral blood flow (CBF) and blood volume induced by rizatriptan
were assessed by positron emission tomography (PET). Eleven healthy volunteers underwent PET
studies before and after rizatriptan administration. Dynamic PET data were acquired after bolus
injection of H 2
15 O to analyze CBF and arterial-to-capillary blood volume (V 0 ) images using the three-
weighted integral method. After a baseline scan, three further acquisitions were performed at 40 to
50, 60 and 70 to 80 mins after drug administration. Global and regional differences in CBF and V 0
between conditions were compared using absolute values in the whole brain and cortical regions, as
well as statistical parametric mapping (SPM) analysis. The global and regional values for CBF and V 0
decreased significantly after rizatriptan administration compared with the baseline condition.
However, both values recovered to baseline within 80 mins after treatment. The maximal reduction in
global CBF and V 0 was approximately 13% of baseline value. The greatest decrease in CBF was
observed approximately 60 mins after drug administration, whereas the maximal reduction in V 0 was
observed approximately 5 mins earlier. Statistical parametric mapping did not highlight any regional
differences between conditions. Thus, in brain circulation, rizatriptan caused significant CBF and V 0
decreases, which are consistent with the vasoconstrictor effect of triptans on the large cerebral
arteries. The gradual recovery in the late phase from the maximal CBF and V 0 decrease suggests that
rizatriptan does not affect the cerebral autoregulatory response in small arteries induced by CBF
reduction.
