Sera from ten migraineurs were examined in headache free periods and during spontaneous attacks for their capacity to contract the rat fundus and uterus in vitro. Sera from two controls were similarly tested.

A “pool” of vasoactive substances which contracted the rat uterus in vitro was always present in the pre attack stage, during the attack and immediately after the migrainous attack.

The contracting activity of sera from migraineurs was also confirmed on the rat fundus strip in vitro. These sera contained serotonin or a serotonin-like substance. The level of this contracting substance in the sera from migraineurs was lowest during migraine attacks.

Control sera also induced rat uterus contractions in vitro. However, this contracting activity was not always present, whereas sera from migraineurs always contracted rat uterus preparations during migraine headache.