Effect of aggregating agents and their inhibitors on the mean platelet shape.

The ;swirling' seen when platelet-rich plasma is stirred is caused by the average asymmetry of the platelets and a technique for recording the swirling is reported. After the addition of adenosine diphosphate, 5-hydroxytryptamine, thrombin, and collagen, platelets become rounded and more symmetrical immediately before they become sticky. Monoiodo-acetate and adenosine prevent both the change in shape and sticking whereas E.D.T.A. and p-tosyl arginine methylester prevent sticking but the shape still changes. Adrenaline produces sticking but no change in shape. The effects of temperature and E.D.T.A. are also reported. All these findings are discussed and diagrammatic representations of some reactions are tentatively proposed.