Effect of heparin on platelet economy in dogs

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Abstract
Studies in 22 dogs show that platelet survival is prolonged by moderate doses of heparin but, if dosage is progressively increased, platelet survival attains a maximum value and thereafter declines. Platelet turnover shows a reciprocal effect but the platelet count is very little affected. In 5 further dogs it was found that about 16 hr. after doses of heparin comparable to the maximum used in the 1st study, red cells and platelets could be demonstrated in the lymph. Platelet-rich plasma prepared from dogs at this stage showed normal platelet aggregation to ADP, a suppressed response to collagen, and no platelet aggregation to thrombin. These observations raise the possibility that high doses of heparin interfere with the mechanism maintaining the normal integrity of the vascular wall, leading to escape of red cells and platelets into the extravascular space. This may be related to some function of the platelet.