Effects of sumatriptan on cerebral blood flow under normo- and hypercapnia in rats

To investigate further the pharmacological mechanism of an anti-migraine drug, sumatriptan, a 5-HT_1B/1D receptor agonist, we studied its effect on the cerebral circulation in seven anaesthetized rats, particularly during hypercapnia. After injection of 0.6 or 6.0 μg/kg sumatriptan succinate, no significant change in cerebral blood flow (CBF) was observed either in the striatum or in the parietal cortex. The increase in CBF both in the parietal cortex and the striatum during 5% CO₂ inhalation was significantly less when sumatriptan succinate 6.0 μg/kg was injected. Sumatriptan appeared to have a vasoconstrictor effect on the relaxed vessels by CO₂ inhalation. This mechanism might be attributable to vasoconstriction through activation of 5-HT_1B receptors located in the vascular smooth muscle rather than 5-HT_1B receptors in the vascular adventitia.