Heparin, myosin and haemostasis: role of vasal muscular component in bleeding effect

The effect of three different molecular weight heparins, naturai -12 KD, low molecular weight heparin (LMW-H) - 5 KD and Oligo-heparin (Oligo-H) - 2 KD, on coagulation system, bleeding time and myosin ATPase activity was compared. Heparins effect on coagulation system depends on molecular weight. In particular, APTT and AXa activities decrease with thè molecular weight. Oligo-H shows to have bleeding effects on tail transection bleeding model as naturai heparin. Bleeding effect is removed by locai administration of ATP. Myosin ATPase activity is inhibited by heparins, independently on thè molecular weight. In fact, the Km is thè same, calculated for myosin in presence of thè three heparins. Heparins are competitive inhibitors of enzymatic activity (Km is double in comparison with thè control at 25 ug of heparins).We confimi thè importance of vasai muscular component in haemostasis and in the bleeding effect of heparins.