Vascular effects of ergot alkaloids: a study on human basilar arteries

Postmortem examinations on human basilar arteries were performed in vitro by recording isometric tension from spiral strips in tissue baths at 37 degrees C. Antagonism of 5-HT by ergotamine, dihydroergotamine and methysergide was of the non-competitive type, that of noradrenaline was either absent (i.e. ergotamine) or considerably weaker. In addition each ergot alkaloid acted as a partial agonist in the following order of efficacy: ergotamine greater than dihydroergotamine greater than methysergide, producing pD2 values of 9.30, 9.60 and 7.10 respectively. Evidence is provided that the stimulant activity of ergotamine is mediated through 5-HT receptors. The present results are compared to those obtained on isolated human vein strips as well as to those on canine blood vessels.