Some substances with proposed digitalis-like effects evaluated on platelet functions sensitive for cardiac glycosides.

1. The effects of progesterone, corticosterone 21-acetate, chlormadinone acetate, dehydroepiandrosterone 3-sulfate and lysophosphatidylcholine were tested on 86Rb-uptake, 3H-5-HT-uptake, ADP-induced aggregation and 5-HT-induced shape change in human platelets. Ouabain and digoxin were used for reference. 2. Ouabain and digoxin 10(-5) M inhibited 86Rb-uptake by more than 85%, and chlormadinone acetate 10(-5) M by 20%. The other substances had no effects. 3. Ouabain and digoxin were potent inhibitors on 3H-5-HT-uptake, whereas chlormadinone acetate had no effect. 4. Ouabain and digoxin increased ADP-induced aggregation but chlormadinone acetate decreased it. 5-HT-induced shape change was decreased by ouabain and digoxin, and to a lesser extent by chlormadinone acetate and its vehicle (ethanol 1.0%).