Amplifying effect of sumatriptan on noradrenaline venoconstriction in migraine patients

The venoconstrictive activity of sumatriptan and its interaction with noradrenaline (NA)- and 5-hydroxytryptamine (5HT) venoconstriction was studied in vivo in the hand vein of migraineurs. Sumatriptan, injected at increasing doses into the vein, caused local venoconstriction after a 500 microgram dose, comparable to that induced by 0.5-1 micrograms of 5HT. This venoconstriction was completely inhibited by low doses of ketanserin (5 micrograms). Subcutaneous sumatriptan (6 mg) provoked a minor increase in vein tone, lasting less than 30 min. Non-venoconstrictive doses of sumatriptan (10-100 micrograms), injected in the hand vein, produced an amplification of NA-venoconstriction but not of 5HT-induced venoconstriction. A similar increased effect was displayed by subcutaneous sumatriptan (6 mg) for at least 1 h. Sumatriptan appears to cause peripheral venoconstriction only at high doses locally applied (in the hand vein), by acting on 5HT2 receptors. Clinical subcutaneous doses (6 mg) do not show significant venoconstrictive effects. The amplifying effect on NA venoconstriction, also caused by 5HT, ergotamine and dihydroergotamine in human cranial arteries, may be important in explaining the therapeutic action of sumatriptan in migraine attacks.