Platelets and Thrombosis

Donné, a French physiologist, seems to have been the first, in 1842, to describe platelets. (9) He called them: ‘globulins du chyle’, or lymph particles, and believed them to be precursors of white blood cells. Others at that time thought they were organisms, or dismissed them as cell debris.

The physician Osler, however, recognised that platelets play a part in thrombosis, and in 1874 he described platelet pseudopodia and their adherence to fibrin when stimulated.(10 )

Nevertheless, the role of platelets and their part in thrombosis was long debated and it was not until perhaps the late 1950’s that there was general agreement about their role in coronary and other thrombotic processes.

In fact, a vast amount of work has led to the present understanding of platelets and their role in thrombosis. Papers of particular relevance were published by Haerem in 197411 who showed that tiny platelet emboli could often be found in the coronary micro-circulation of cases of sudden death in which there was no major coronary thrombus and Michael Davies in 1984, who showed that a platelet plug could be found at the head of almost every thrombus in the coronary vessels.(12) These and other reports around this time focused attention on platelets as a key factor in myocardial infarction.

Early laboratory work on platelets described their role in bleeding disorders and a low platelet count, or thrombocytopenia, was first described in 1905.(13) Attempts were therefore made to measure the ‘stickiness’ of platelets but the tests to do this were all very poorly reproducible. In 1962 O’Brien (14) and Born (15) simultaneously described methods of measuring platelet aggregation and this greatly advanced the study of platelet function. Furthermore, it encouraged the study of the role of platelets in thrombosis, rather than in bleeding.