Effect of a collagen derived octapeptide on different steps of the platelet/collagen interaction

The interaction of platelets with collagen involves short aminoacid sequences which recur along the fibres. Platelet aggregation by collagen and serotonin release is inhibited by a synthetic octapeptide LYS-PRO-GLY-GLU- PRO-GLY-PRO-LYS- derived from type III collagen. In contrast, this octapeptide inhibits only weakly the retention of platelets labelled with 111Indium to collagen, suggesting that it has a limited effect on platelet adhesion. Preincubation of the octapeptide with platelets inhibits the rise of cAMP level caused by activating adenylate cyclase by various concentrations of PGI2. The octapeptide at 5 mM reverses the inhibition by PGI2 of the adhesion of platelets to collagen. These results suggest that the octapeptide affects the intrinsic activity (manifested as platelet aggregation and secretion) more than the recognition of collagen by its receptor (manifested by adhesion).