Anticoagulant activities of four unfractionated and fractionated heparins

Four commercial heparins, two of bovine lung and two of porcine mucosal origin, have been fractionated by gel filtration (and one of them also by ion-exchange chromatography) to yield different fractions whose mean MW_s lie in the MW range 7,000–26,000. Three plasma anticoagulant assays have been used to measure the specific activities of the heparin fractions, a kaolin-cephalin clotting time method (KCCT), a calcium-thrombin clotting time method (TCT) and a specific anti-factor Xa assay. The two unfractionated mucosal heparins were found to have higher specific activities when measured in the anti-Xa assay compared to the KCCT assay, while the unfractionated beef lung heparins had lower anti-Xa than KCCT activities. An increase with MW of the heparin fractions was found in specific activities as measured by KCCT and TCT assays over most of the MW range. The low MW heparin fractions (less than 10,500) from all of the heparins had specific activity ratios, KCCT:anti-Xa and TCT:anti-Xa, which were always less than unity. These specific activity ratios increased with increasing MW, usually to greater than unity for the highest MW (greater than 22,000) fractions. There was a tendency for these specific activity ratios to be higher for the beef lung than the mucosal heparin fractions at a given MW. The ability of heparin fractions to inhibit the thrombin induced aggregation of platelets in citrated platelet-rich plasma increased with MW over most of the MW range studied and seemed to follow the specific activities of the fractions when measured by TCT or KCCT assays.