Viscous metamorphosis, clot retraction and other morphologic alterations of blood platelets

¹ Clotting Mechanisms Section, Division of Metabolism and Enzyme Studies, Sloan-Kettering Institute for Cancer Research, New York City

Some samples of washed platelets undergo viscous metamorphosis (VM) in oxalated or citrated plasma, oxalated serum or serum poor in prothrombin. Other samples only undergo VM when serum containing residual prothrombin is used and thrombin is evolved when platelets are added. Thrombin produces VM at pH 7.4 but not at pH 6.1 or in isotonic saline. Treatment of thrombin with diisopropylfluorophosphate (DFP) or addition of heparin plus serum inhibits VM. Spreading of platelets upon glass, and balloon formation are not closely correlated with VM. Clot retraction in a purified system often occurs without added buffer or glucose, but is always very marked in the presence of both buffer and glucose. Calcium binding anticoagulants prevent VM and clot retraction. The inhibition is reversed by calcium and, to a lesser extent, magnesium. Cyanide (4 or 5 x 10^–3 m) does not inhibit VM or retraction in a purified system but inhibits retraction of platelet-rich plasma, especially when it is clotted with thrombin. At this concentration, fluoride has a variable effect. Mercuric chloride is an effective inhibitor of both VM and retraction at concentrations of 10^–4 m and below.