Summary
An in vitro system is described in which adhesion of blood platelets to washed and tannic acid-treated
red cells was assayed quantitatively by microscopic observation. ADP, epinephrine
and TAME produced a reversible increase in platelet adhesiveness which was antagonized
by AMP. With Evans blue, polyanetholsulfonate, phthalanilide NSC 38280, thrombin and
heparin at concentrations above 1-4 u/ml the increase was irreversible. The ADP-induced
increase in adhesiveness was inhibited by sodium citrate, EDTA, AMP, ATP and N-ethylmaleimide.
EDTA, AMP and the SH-blocker N-ethylmaleimide also reduced spontaneous platelet adhesion
to red cells. No significant effects were observed with adenosine, phenprocoumon,
5-HT, phthalanilide NSC 57155, various estrogens, progestogens and fatty acids, acetylsalicylic
acid and similarly acting agents, hydroxylamine, glucose and KCN. The method may be
useful for the screening of thrombogenic and antithrombotic properties of drugs.