The Effect of Prostaglandin E₁ on Platelet Function in Vitro and in Vivo

S ummary Low concentrations of prostaglandin E 1 (PGE 1 ) inhibit ADP‐induced aggregation in pig and rabbit citrated platelet‐rich plasma and in suspensions of washed platelets. Higher concentrations also inhibit the initial change in shape induced by ADP and the release of platelet ATP, ADP and serotonin caused by stimuli such as collagen, thrombin, antigen‐antibody complexes and gamma‐globulin‐coated polystyrene particles. PGE 1 is not taken up by platelets and its effects can be removed by resuspending platelets in fresh medium. Immediately following an intra‐arterial injection, ADP‐induced platelet aggregation is suppressed, but after 5 min the response returns to normal. PGE 1 inhibits haemostasis in rabbits when given as a continuous infusion. It is concluded that the effect of PGE 1 on haemostasis involves inhibition of the release of ADP from platelets exposed to collagen and thrombin, and inhibition of ADP‐induced aggregation.