Adrenaline/PAF acether synergism on human platelets: involvement of Hydergine.

Adrenaline stimulates platelet aggregation via the alpha 2-adrenergic receptor; the resultant aggregation is blocked by aspirin. In conjunction with low concentrations of PAF-acether, adrenaline induces aggregation which is not susceptible to blockade by aspirin. Hydergine and other alpha 2-adrenergic antagonists block the specific aggregant action of adrenaline as well as the synergic effect in the presence of PAF-acether.