The effects of three antimigraine drugs--ergotamine, dihydroergotamine, and methysergide--on the distribution of flow throughout the cephalic circulation of the cat were studied, using microspheres of a suitable size to separate capillary flow from flow through the arteriovenous anastomoses. Ergotamine and dihydroergotamine significantly decreased the fraction of carotid blood flow shunted through the arteriovenous anastomoses, a mode of action that reemphasizes the need for further clinical studies on the involvement of arteriovenous anastomoses in the pathophysiology of migraine headaches.
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Spierings et al. (1980) studied this question.