Changes in tension were monitored isometrically on spiral strips of freshly obtained bovine basilar arteries. Ergotamine (E), dihydroergotamine (DHE), methysergide (M) and pizotifen (BC-105) displaced the concentration-response curve for 5-HT in a noncompetitive way and in similar concentration ranges as indicated by the pD' 2(60 min) values of the three ergot alkaloids (E: 9.2, M: 9.1, DHE: 8.8) and the pD' 2(30 min) value (8.9) of BC-105. The ergot alkaloids but not BC-105 also exhibited considerable stimulating activity. The calculated pD2 values were 8.8 for E, 8.6 for DHE and 6.6 for M. Relative to 5-HT (= 1) the intrinsic activities were 0.4, 0.2 and 0.1 for E, DHE and M, respectively. BC-105 was nearly equipotent in antagonizing responses to 5-HT, E and DHE suggesting that both ergot alkaloids act as noncompetitive dualists at the 5-HT receptor. The results suggest that the strong stimulant rather than the blocking activity at the 5-HT receptor of ergotamine may be an important property for its therapeutic efficacy in migrainous attacks.
The hypothesis that pro-inflammatory spasmogens may be generated locally in the vessels of the head by neurohumoral stimuli has been tested using an isolated extracranial vascular bed from the rabbit. No spasmogen release was detected after adenosine triphosphate, histamine, acetylcholine or noradrenaline and was seen rarely after tyramine and 5-hydroxytryptamine. Both sympathetic nerve stimulation and periods of vascular stasis released spasmogen, probably an E-type prostaglandin. The local generation of pro-inflammatory substances by excess sympathetic stimulation and/or vascular stasis might contribute to the development and maintenance of the acute migraine attack.