Effects of sumatriptan on the cerebral intraparenchymal microcirculation in the cat

1 Sumatriptan, a 5‐hydroxytryptamine (5‐HT)1‐like receptor agonist, is effective against the headache of migraine. The effects of sumatriptan injected via the carotid artery on the cerebral microcirculation were studied in 10 anaesthetized cats. 2 The local cerebral blood volume (CBV), mean transit time of blood (MTT) and cerebral blood flow (CBF) in the parieto‐temporal cortex were measured by a photoelectric method. CBV represents the cumulative dimensions of the cerebral microvessels. 3 Sumatriptan at 5 and 50 μg kg−1 had no significant effects on the CBV, MTT, CBF, and mean arterial blood pressure (MABP); 500 μg kg−1 of sumatriptan reduced the CBV, prolonged the MTT, and decreased the CBF (approximately −20%) without affecting the MABP. Sumatriptan, 5 mg kg−1, elicited transient reductions in CBV and CBF, which were attributable to the rapid and marked falls of MABP seen with this dose. 4 Thus, while a high dose of sumatriptan (500 μg kg−1) exhibits direct vasoconstrictor actions on the cerebral vessels, low doses of sumatriptan, within the therapeutic range, elicit no vasoconstriction. The data do not support a vasoconstrictor action of sumatriptan playing a primary role in reversing the headache of migraine.