“…(e) Blockade of 5-hydroxytryptamine vasoconstriction. Dihydroergotamine, like ergotamine, is a potent antagonist of the blood pressure rise produced by 5-hydroxytryptamine in vivo (Hotovy & Roesch, 1958;Outschoorn & Jacob, 1960) vasoconstrictor responses of isolated rabbit ears (Gaddum & Hameed, 1954) hind limbs (Meier & others, 1957) aorta (Innes, 1962b) and auricular artery (Carroll & others, 1972;Fozard, 1973). Also like ergotamine, the antagonism is selective in that the stimulant effects of 5-hydroxytryptamine on extra-vascular smooth muscle are little affected even by high concentrations of dihydroergotamine (Gaddum & Hameed, 1954;Bhattacharya, 1955;Salzmann & Kalberer, 1973).…”