Long-term ergotamine abuse: effect on adrenergically induced mydriasis.

The mydriatic action of sympathomimetic eyedrops after a therapeutic dose of ergotamine was measured in migraine patients with and without histories of long-term ergotamine abuse. Mydriasis induced by the postsynaptic alpha 1-agonist phenylephrine was similar in both groups of patients tested, whereas pupillary dilation caused by the release of noradrenaline tyramine was markedly greater in patients with histories of ergotamine abuse. The enhanced response to tyramine disappeared after drug withdrawal. These findings indicate that continuous ergotamine medication causes a reversible alterations in iris sympathetic transmission. This manifestation may reflect a central inhibition of pupillary sympathetic activity.