Investigation of chemical mediators for shear activation of platelets by filter bleeding time

• Published in: Japanese Journal of Stroke Vol. 7; no. 2; pp. 174 - 179
• Main Authors: Uchiyama, Shinichiro, Kobayashi, Itsuro, Maruyama, Shoichi
• Format: Journal Article
• Language: Japanese
• Published: The Japan Stroke Society 1985
• Subjects: ADP; Thromboxane A2
• ISSN: 0912-0726; 1883-1923
• DOI: 10.3995/jstroke.7.174

Chemical mediators for shear-induced platelet activation which might contribute to thrombogenesis in cerebral arteries, particularly in their parts of bifurcations or stenoses, were investigated by using a new in vitro platelet-sensitive technique, Filter Bleeding Time (FBT). FBT is based on progressive decrease of flow rate of citrated blood through a disk filter of woven Dacron under controlled pressure (150 mmHg) as platelet aggregates occlude the filter. FBT was prolonged from 2.0± 1.0 (x ± SD) to 10.4 ± 2.7 min (p<0.002) by a monoclonal antiplatelet antibody (HP1-1D), which is specific for platelet membrane antigens, presumably glycoproteins IIb and IIa. FBT was prolonged from 2.7 ± 1.8 to 6.2 ± 1.8 min (p<0.007) by the combination of CP and CPK, which remove plasma ADP, with ATP, which inhibits the effects of ADP on platelets. Thromboxane synthetase inhibitors (TXI), UK-37, 248 and UK-38, 485 did not affect platelet aggregation to ADP. Platelet aggregation to arachidonate was inhibited by UK-38, 485 in 3 of 6 subjects, designated “responders”. In neither responders nor non-responders FBT was prolonged by this agent. TXI had, however, a synergistic effect on FBT when added with CP/CPK/ATP. Plasma oxyhemoglobin (Hb) increased from 5 ± 2 to 555 ± 52 mg/dl (p<0.001) in human subjects and from 11 ± 6 to 496 ± 435 mg/dl (p<0.04) in canine subjects during passage of blood through the filter. FBT was correlated with the increase of plasma Hb during FBT in canine subjects (r= -0.87). Platelet lysis during FBT was measured by increase of 111Indium-tropolone in platelet-poor plasma. Plasma 111Indium increased from 2.8 ± 1.5 to 5.1 ± 1.3% (p<0.003) during FBT. This shear-induced platelet lysis was inhibited by HP1-1D but not by UK-37, 248. The results above indicate that thromboxane A2 plays a minor role and ADP plays a central role in shear activation of platelets. It should be considered that ADP is liberated not only from dense granules released from platelets but also from ruptured cytoplasms of erythrocytes and platelets.