The physiological function of heparin is not completely understood. It is found only in trace amounts in normal circulating blood. It exerts an antilipemic effect by releasing lipoprotein lipase from endothelial cells; heparinlike proteoglycans produced by endothelial cells have anticoagulant activity. Heparin decreases platelet and inflammatory cell adhesiveness to endothe-lial cells, reduces the release of platelet-derived growth factor, inhibits tumor cell metastasis, and exerts an an-tiproliferative effect on several types of smooth muscle.
Therapy with heparin occurs in an inpatient setting. Heparin inhibits both in vitro and in vivo clotting of blood. Whole blood clotting time and activated partial thromboplastin time (aPTT) are prolonged in proportion to blood heparin concentrations.
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