The atherogenic mechanism of homocystinemia has been defined by measuring endothelial cell loss and regeneration, platelet consumption, and intimal lesion formation in a primate model. Three groups of baboons were studied: (a) 8 control animals; (b) 15 animals after 3 mo of continuous homocystinemia; and (c) 11 animals after 3 mo of combined homocystinemia and oral treatment with dipyridamole. Experimental homocystinemia caused patchy endothelial desquamation comprising about 10% of the aortic surface despite a 25-fold increase in endothelial cell regeneration. Neither endothelial cell loss nor regeneration was changed significantly by dipyridamole. Homocystine-induced vascular deendothelialization produced a threefold increase in platelet consumption that was interrupted by dipyridamole inhibition of platelet function. All homocystinemic animals developed typical arteriosclerotic or preatherosclerotic intimal lesions composed of proliferating smooth muscle cells averaging 10-15 cell layers surrounded by large amounts of collagen, elastic fibers, glycosaminoglycans, and sometimes lipid. Intimal lesion formation was prevented by dipyridamole therapy. We conclude that homocystine-induced endothelial cell injury resulted in arteriosclerosis through platelet-mediated intimal proliferation of smooth muscle cells that can be prevented by drug-induced platelet dysfunction.

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Homocystine-induced arteriosclerosis. The role of endothelial cell injury and platelet response in its genesis.

Summary: Methods have been developed for the preparation of suspensions of washed platelets from humans Heparin is used in the washing fluids to prevent: thrombin generation and apyrase is used to prevent adenine nucleotide accumulation Platelets suspended in Eagle's tissue culture medium containing albumin were more responsive to ADP than platelets in Tyrode's-albumin solution Addition of fibrinogen is required for maximum sensitivity to ADP-induced aggregation These platelets can be stored for 4 hr or more at 37°C in the presence of apyrase and maintain their ability to aggregate upon the addition of low concentrations of ADP

Without apyrase the platelets gradually become insensitive to ADP upon storage at 37°C; this is presumably caused by the accumulation of ADP in the suspending fluid because sensitivity can be partially restored by the addition of apyrase and further incubation

Preparation of Suspensions of Washed Platelets from Humans

Homocystinemia. Vascular injury and arterial thrombosis.

The value of the standardized template bleeding time was studied in 100 normal subjects and 136 patients with various disorders. With normal platelets the bleeding time in this test is 4.5 ± 1.5 minutes (± 1 S.D.) when the circulating platelet concentration exceeds 100,000 per microliter, and is 30.5 – (platelet count per μl/3850) minutes at platelet counts between 100,000 and 10,000 per microliter. More prolonged bleeding times reflect impaired platelet function, as associated with acetylsalicylic acid ingestion, uremia, or von Willebrand's disease. In contrast, bleeding times shorter than predicted with normal platelets are due to increased hemostatic competence of young platelets, associated either with idiopathic thrombocytopenic purpura or with bone-marrow recovery after chemotherapy. The standardized bleeding time measures the overall hemostatic role of platelets in vivo, and is thus suitable for systematic screening.

https://www.nejm.org/doi/pdf/10.1056/NEJM197207272870401?listPDF=true

The bleeding time as a screening test for evaluation of platelet function.

Effect of acid and pepsin on blood coagulation and platelet aggregation. A possible contributor prolonged gastroduodenal mucosal hemorrhage.

Effect of adenosine nucleotides on platelet aggregation and clotting time.

The acceleration of blood coagulation in vivo by adrenaline was first demonstrated by Vosburgh and Richards in 1903. They showed in man that adrenaline in doses of 7 μg. per kg. body weight shortened the coagulation time by about 50 per cent. Subsequent studies led to conflicting conclusions until the experiments of Cannon and Gray in 1914, who showed that small doses of adrenaline promoted coagulation, but that larger doses inhibited it. This was confirmed by later investigators (Waldron, 1951; Forwell and Ingram, 1957) but, so far as we know, the effect in normal animals of adrenaline on thrombus formation, as distinct from coagulation, has not been explored. More recently, evidence has been presented that adrenaline increases Factor-VIII activity (Ingram, 1961), shortens platelet survival and increases platelet turnover (Adelson, Rheingold, Parker, Buenaventura and Crosby, 1961; Ozge and Mustard, 1964). Recently, Mitchell and Sharp (1964) and O'Brien (1963) have shown that adrenaline promotes platelet aggregation in vitro.

In the present study we have directed our attention to the effect of this drug on blood coagulation, platelets and thrombus formation. Quantitative study of thrombus formation has been made possible by the development of a standard extracorporeal circulation which allows precise measurement (Downie, Murphy, Rowsell and Mustard, 1963). In view of the findings of earlier investigators studying coagulation, it seemed important to determine how dosage levels affect the results.

B. Hegardt

Papers

Effect of adenosine nucleotides on platelet aggregation and clotting time.

Adrenaline and Experimental Thrombosis

The effect of adenine nucleotides on thrombus formation, platelet count, and blood coagulation.