Investigations on the mode of action of ergotamine in the isolated femoral vein of the dog.

1 Experiments on spiral strips cut from the femoral vein of dogs suspended in Krebs-Henseleit solution were carried out.2 Ergotamine caused stimulation in concentrations about 350 times lower than noradrenaline (ED(50) of ergotamine = 2.2 x 10(-9) M; ED(50) of noradrenaline = 7.6 x 10(-7) M), but the maximal responses to ergotamine were only about one third those to noradrenaline.3 The pA(2) value of ergotamine against noradrenaline was 8.8.4 The effects of ergotamine can be blocked by prior administration of phentolamine. The pA(2) value for phentolamine against ergotamine was 6.8 and the pA(2) value for phentolamine against noradrenaline was 7.5.5 It is concluded that the stimulant action of ergotamine on smooth vascular muscle probably is mediated mainly via alpha-adrenoceptors.