Dual effect of dihydroergotamine and dihydroergotoxin in isolated human femoral veins and arteries.

In human femoral vein strips, dihydroergotamine and dihydroergotoxin caused a slowly proceeding, long-lasting increase in tone. Dihydroergotamine had markedly higher affinity than noradrenaline, it possessed nearly the same intrinsic activity as noradrenaline. Dihydroergotoxin was less effective than dihydroergotamine. In isolated femoral artery strips, dihydroergotamine showed lower affinity and lower intrinsic activity in terms of noradrenaline. Dihydroergotoxin had negligible vasoconstrictor effects in arteries. In veins, dihydroergotoxin had a stronger alpha-adrenolytic effect than in arteries. In isolated arteries, dihydroergotoxin was equieffective to dihydroergotamine whose alpha-adrenoceptor blocking effect did not significantly differ in veins and arteries. Our results show that dihydroergotamine at very low concentrations exerted predominantly venoconstrictor effects and, therefore, it is more suited to increase the venous tone than dihydroergotoxin which at low concentrations showed alpha-adrenoceptor blocking activity.