Thrombin regulation of platelet interaction with damaged vessel wall and isolated collagen type I at arterial flow conditions in a porcine model: effects of hirudins, heparin, and calcium chelation

Abstract

The role of thrombin inhibition in platelet vessel wall interaction and thrombus growth was studied under controlled flow conditions. Natural hirudin and recombinant hirudin (r-hirudin), which are specific thrombin inhibitors, were compared with heparinized blood (1.8 +/- 0.2 U/mL) and Ca(2+)-chelated blood in their potential to inhibit platelet interaction and thrombus growth on two biologic vascular surfaces and one immobilized vessel wall component. The substrates were perfused by flowing blood at shear rates typical of patent and stenosed arteries (212 to 1,690/s) for 5 minutes. Platelet deposition was measured by In- 111-labeled platelets. We found that both natural and r-hirudin have similar effects on platelet-substrate interaction. As compared with heparin, platelet deposition to mildly damaged vessel wall and digested collagen type I was not reduced by hirudin or citrate. However, hirudin and citrate significantly reduced platelet deposition to severely damaged vessel wall (platelets x 10(6)/cm2: 93 +/- 10 in heparinized blood v 50 +/- 7 in blood treated with 100 U/mL r-hirudin). Therefore, thrombus growth on areas of severe wall damage is in part dependent on local thrombin production at the site of vascular damage. We also found that hirudin added to heparinized blood reduced platelet deposition to severely injured wall but not to subendothelium or collagen-coated slides. Hirudin added to citrated blood did not affect platelet deposition. Our study indicates that local thrombin generation at the site of severe injury will induce platelet activation and deposition even in the presence of average therapeutic heparin levels that inhibit blood coagulation.

Hepatic and extrahepatic factors critical for liver injury during lipopolysaccharide exposure

“…White blood cells were counted, and a differential count was made on blood smears to verify neutrophil depletion. AN-Ig administration reduced the number of circulating PMNs from 821 Ϯ 200 to 49 Ϯ 8 PMN/mm 3 . This degree of PMN depletion completely eliminates LPSinduced liver injury in vivo (29).…”

Mast Cell–Derived Heparin Proteoglycans As a Model for a Local Antithrombotic

“…The two in vivo experiments in baboons are encouraging regarding the dual antiplatelet and anticoagulant action. 27,28 In the modified Folt model of acute thrombosis in baboons, APAC applied locally on the crush-injured and stenosed arterial site effectively and consistently inhibited thrombosis in the artery under the moderate shear stress, with the flow rate of 100 mL/min and stenosis of 30% until the experiment was interrupted after 120 minutes. When APAC was addressed with the short exposure of sequentially increased stenosis from 60 to 90% the patency of the artery was further maintained.…”

Continuous Registration of Thrombin Generation in Plasma, Its Use for the Determination of the Thrombin Potential

“…Recent research tends to stress the central position of thrombin in the pathogenesis of thrombosis (16,17, sei also 18 and 19 for an overview). Thrombin appears as the pivotal enzyme in haemostasis and thrombosis.…”