Platelet aggregation and inactivation and inhibition of adenosine diphosphate

¹ Department of Pharmacology, Medical Research Laboratories, Chas. Pfizer & Co., Inc., Groton, Connecticut

Adenosine diphosphate (ADP)-induced platelet aggregation in rabbit and rat platelet-rich plasma was used as an index of ADP activity, and as a means of detecting inhibitory activity to ADP. Inactivation of ADP occurred in rabbit and rat plasma, and ADP inhibitory activity appeared in the plasma of both species following incubation with the nucleotide. Platelets were not required for the inactivation of ADP, or for the formation of inhibitory activity, but both processes were enhanced in the presence of platelets. ADP inhibitory activity in rabbit and rat plasma did not resemble that of exogenous adenosine or AMP. The results do not support the assumption that known products of the degradation of ADP are solely responsible for the inhibitory activity. It is concluded that the inhibitory activity may be due to unknown products of the degradation of ADP, or to a factor elicited in response to the presence of ADP in plasma.

Key Words: adenosine diphosphate • inactivation and inhibition in plasma

Submitted on January 19, 1965