Interactions of human blood platelets with three circulating plasma fibrinogens of different molecular weights

The ability of three naturally occurring human fibrinogen species, HMW, LMW and LMW', to support ADP-induced platelet aggregation was investigated and compared to their ability to bind to gel-filtered platelets. Whereas HMW had intact subunit chains, LMW and LMW' had defined lesions in the C-terminal part of one (LMW) or both (LMW') of the A alpha-chains. The ADP-induced aggregation of gel-filtered platelets in the presence of LMW was about 75 per cent of that obtained with HMW (0.2 mumol/l of fibrinogen and 10 mumol/l of ADP). A mixture of equal amounts of LMW and LMW' showed around 50% decrease in aggregation. Compared to these difference in aggregation co-factor function, direct binding to gel-filtered platelets was less affected by the A alpha-chain degradation. However, a difference between LMW, LMW' and HMW binding was significant when the fibrinogens labelled with two different isotopes of iodine were present simultaneously. These results demonstrate that naturally occurring plasma fibrinogens differ in their interactions with platelets. As the HMW/LMW ratio changes during the acute phase, this may be of physiological significance.