The vasoconstrictor activity of sumatriptan and ergotamine were compared by injecting these drugs in the hand vein of migraine subjects. We used the “venotest method”, which permits the evaluation of the venoconstrictor effect of small doses of drugs, acting locally in the hand vein.
Sumatriptan injected at increasing doses in the hand vein provoked contraction only at high doses (500 μg): venoconstriction lasted 5–15 minutes and was similar in intensity and duration to that induced by 0.5-1 μg of 5-hydroxytryptamine (5-HT). Likewise, ergotamine induced contraction only at a dose of 50 μg: this venoconstrictor effect was long lasting (at least I hour). Ergotamine-induced hand vein contraction, almost completely inhibited by ketanserin, seems mediated at least in part by 5-HT 2 receptors, like the one induced by 5-HT and sumatriptan, already observed in a previous study.
Clinical doses of ergotamine (0.25 mg intramuscular) and of sumatriptan (6 mg subcutaneous) do not provoke hand vein contraction for at least I hour: this could be due to a low activity of these drugs on the 5-HT 2 vein receptors or a technique that is unsuitable to detect the vasoconstrictor effect of drugs given by the systemic route.
The long lasting venoconstrictor effect of ergotamine may be due to a slow dissociation from receptor sites. The short vasoconstriction induced by sumatriptan could account for the recurrence of headache in many sumatriptan-treated migraine subjects.