Torstein Hovig

Summary 1. Blood platelet aggregation was induced by addition of saline “extract” of tendons to citrated PRP (aggregation time 50—60 seconds). The aggregates were sedimented by centrifugation, and aggregating activity was demonstrated in the supernatant (termed supernat. A) with an aggregation time of about 15 seconds. 2. It was demonstrated that the activity of the supernatant was due to ADP released from the platelets. 3. The conclusion is drawn that the aggregation reaction initiated by the tendon “extract” can be divided into two steps: 1. release of ADP from the platelets, 2. aggregation caused by released ADP. 4. The observations are discussed in relation to the formation of platelet plugs in vivo.

S ummary . Investigations of the haemostatic functions in three patients with the Wiskott‐Aldrich syndrome are presented. All patients had severe thrombocytopenia and prolonged bleeding times. The platelets had abnormal morphology with reduced size and variations of shape. Electron microscopy revealed ultrastructural abnormalities with a reduced number of organelles, and many of the platelets contained large numbers of tubules. Platelet electrophoretic mobility in citrated plasma was not reduced by collagen, and platelet aggregation by collagen and ADP was deficient. Biochemical studies revealed a lack of the storage pool of adenine nucleotides. Platelet adhesiveness in vitro in whole blood was reduced. Platelet factor‐3 release by kaolin, ADP and freezing and thawing was normal in one and reduced in another of the patients. Platelet survival studies showed a normal survival time of normal donor platelets in one patient, while autologous platelets had a markedly reduced survival time in two of the patients. The bone marrow contained normal numbers of megakaryocytes. By electron microscopy of the bone marrow, blood platelets were found to be phagocytosed by macrophages and reticulum cells. The main cause of the thrombocytopenia is most probably incrcased peripheral destruction of platelets. It is suggested that the qualitatively defective platelets are recognized in the reticulo‐endothelial system as foreign particles and phagocytosed.

Summary Rabbit blood platelet aggregates were produced in vitro by addition of rabbit tendon “extract” to citrated platelet-rich plasma. The aggregating activity was not due to presence of adenosine diphosphate in the “extracts” and was unrelated to blood coagulation. The aggregating principle was destroyed by heating of the “extract” to 60° C for 15 minutes or by incubation with collagenase for 1 hour at 37° C. The aggregating effect was associated with particles which were sedi- mented by centrifugation for 30 minutes at 10,000 G. By means of electron microscopy the particles were identified as cross-striated collagen fibrils.