Influence of dihydrolysergic acid amide on serotonergic and alpha-adrenergic receptors in human blood platelets and femoral veins in vitro.

The effect of dihydrolysergic acid amide (DLSA) on responses of human blood platelets and isolated postmortem femoral veins to serotonin and catecholamines was studied in vitro in comparison to dihydroergotamine (DHE). DLSA inhibited the 5-HT-potentiated, ADP-induced platelet aggregation in approximately the same concentration range as DHE. It was three orders of magnitude less potent in inhibiting the adrenaline-induced aggregation and specific binding of 3H-yohimbine to intact platelets than DHE. In femoral vein strips, DLSA caused an increase in tone in the same concentration range (0.01-1.0 mumol/l) as DHE; however, its efficacy was somewhat lower. At concentrations of 0.1 to 1.0 mumol/l it antagonized the 5-HT-induced contractile response in a noncompetitive manner, the antagonist potency being one order of magnitude lower than that of DHE. DLSA (1 mumol/l) did not inhibit the noradrenaline-induced venoconstriction. The results show that DLSA possesses agonist activity in femoral veins and 5-HT-antagonist activity in platelets and veins.