A Study of the Variable Response of Human Platelets to Collagen: Relation to Aspirin-induced Inhibition of Aggregation

Soluble collagen was extracted from human skin. The solutions of this collagen were storage-stable, and, in some samples of platelet-rich plasma, induced aggregation when diluted up to 1,000-fold. An examination of platelet aggregation in 20 normal subjects revealed a broad range of platelet responsiveness to collagen, as defined by the least collagen concentration needed to initiate platelet aggregation. The inhibitory effects of acetylsalicylic acid (ASA) were evaluated both in vitro and in vivo. There was a direct correlation between the collagen concentration needed to demonstrate ASA inhibition of platelet aggregation and initial platelet sensitivity to collagen. ASA inhibition was obscured if too-large collagen concentrations were used to study the aggregation of collagen-sensitive platelets. The quantitative relationships between collagen, ASA, and platelets have an important bearing on the estimation of ASA as a platelet antiaggregating agent.