Evidence for the presence of a new plasma factor which acts synergistically to ADP induced platelet aggregation.

The existence of a new factor (AF) in mice acting synergistically with known proaggregatory stimuli has been suggested by the present study in the plasma of mice challenged with intravenous collagen and adrenaline. Indomethacin, nordihydroguaretic acid (NDGA), BW 755C, phentolamine, cimetidine and ketanserin could not block the response of AF. Activity of the factor remained unaltered after treatment with pancreatic phospholipase A2, collagenase, CP/CPK, trypsin and heparin. Fractionation of the plasma indicated the presence of AF in acetone precipitate. Activity was destroyed by pronase and it was lost after dialysis and charcoal treatment. Existence of such a factor which is heat resistant, is of low molecular weight and is proaggregatory in nature in the thrombotic mice plasma and which requires calcium ions for the expression of its activity, has not been reported earlier.