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Ergotamine stimulates spiral strips from dog saphenous veins in concentrations about 2,000 times lower than that of noradrenaline, but its maximal effect is only 20% compared to that of noradrenaline. Phentolamine antagonizes the ergotamine effects. The pA2 value for phentolamine against ergotamine is 6.94, and for phentolamine against noradrenaline it is 6.96. Cocaine potentiates noradrenaline effects but does not change ergotamine effects. The results suggest that the venoconstrictor activity of ergotamine is mediated mainly via stimulation of α-adrenoceptors.
Müller‐Schweinitzer et al. (Thu,) studied this question.