Effect of ergotamine on cranial arteriovenous shunting in experiments with constant flow perfusion

The effect of the antimigraine drug, ergotamine, was studied on the distribution of flow throughout the cranial microcirculation of the cat, using microspheres suitable in size to separate capillary flow from flow through the arteriovenous anastomoses. A constant flow perfusion experiment was used in order to eliminate the secondary effect of ergotamine on the microcirculation through a reduction in carotid blood flow per se. Under the experimental conditions, ergotamine decreased in a dose-dependent way the fraction of perfusion flow shunted through the arteriovenous anastomoses. This mode of action of ergotamine sheds new light on the so-called migraine shunt theory.