Biomedical subjects

Junichiro Yamamoto

Publications and source records attributed to Junichiro Yamamoto.

27 records · Page 2Linked to original sources

PubMed2003

Görög Thrombosis Test: a global in-vitro test of platelet function and thrombolysis.

This is the first laboratory evaluation of a new instrument, designed to test both platelet function and thrombolytic activity from a native blood sample, in vitro. The inventor assumed that the reduction and arrest of blood flow was due to activation, aggregation and stabilized thrombus formation by shear-activated platelets, and that re-establishment of flow was due to thrombolysis. Morphologic and functional studies presented here confirm these mechanisms. In vitro tests provided incontestable evidence for the principal role of platelets in the obstruction of flow (occlusion time) and for thrombolysis as the principal mechanism underlying the restoration of blood flow (lysis time). In addition to aggregation, it is the explosive generation of thrombin by shear-activated platelets that results in the formation of an occlusive haemostatic thrombus. Anticoagulation of blood completely prevented occlusion. Platelet-rich thrombus formation (occlusion time) was dose-dependently inhibited by monoclonal antibody against platelet glycoprotein (GP) Ib (6B4 and 12E4), aurin tricarboxylic acid, monoclonal antibody against platelet GPIIb/IIIa (MA-16N7C2 and abciximab), a synthetic GPIIb/IIIa antagonist (TAK-029), thrombin inhibitor (argatroban), and anti-von Willebrand factor, but not by anti-fibrinogen. Plasminogen activator streptokinase (Varidase) and tissue-type plasminogen activator (Monteplase) dose-dependently enhanced thrombolysis (lysis time) without affecting platelet function (occlusion time). The test is specific for thrombolysis. The plasmin inhibitor tranexamic acid prevented plasminogen activator-induced thrombolysis, while inhibition of clot retraction by cytochalasin B did not affect the lysis time. This rapid and sensitive global test of platelet function and thrombolytic activity could be of great value both in research and in clinical practice.

Adult↗

PubMed2003

Shear-induced in-vitro haemostasis/thrombosis tests: the benefit of using native blood.

The historical development of in-vitro bleeding time tests, using solely shear forces to initiate haemostatic plug formation, in the absence of the vessel wall or its components, is described. Techniques that have no potential for routine use in clinical practice, such as flow chambers and cone-and-plate viscometers, are excluded. The problems related to the use of citrated blood in platelet function tests are discussed. In light of the pivotal role of thrombin and platelet-dependent thrombin generation in haemostasis/thrombosis, the advantage and clinical benefits of testing unadulterated native blood is discussed.

Bleeding Time↗

PubMed2003

Suppression of argatroban-induced endogenous thrombolysis by PKSI-527, and antibodies to TPA and UPA, evaluated in a rat arterial thrombolysis model.

We have previously confirmed, using a rat mesenteric arteriole thrombolysis model, that thrombin inhibition induces endogenous thrombolysis in vivo. In addition, we have shown that thrombin-activatable fibrinolysis inhibitor (TAFI) plays a role in the down regulation of endogenous thrombolysis. However, the mechanism of endogenous thrombolysis or spontaneous plasmin generation in vivo remains unclear. It has been shown in an in vitro system that plasma kallikrein activates pro-urokinase (pro uPA) and/or plasminogen, resulting in plasmin generation. These findings suggest that spontaneous fibrinolysis might be mediated by tPA and plasma kallikrein-dependent uPA. The aim of the present study was to examine whether these mechanisms play a dominant role in endogenous thrombolysis in vivo, using our rat mesenteric arterial thrombolysis model. Argatroban infusion enhanced endogenous thrombolysis. PKSI-527, anti uPA and anti tPA IgGs suppressed argatroban-induced thrombolysis. Also, the antibody IgG preparations suppressed endogenous thrombolysis in the absence of argatroban. In the presence of PKSI-527, anti tPA IgG was more effective than anti uPA IgG in suppressing argatroban-induced thrombolysis. The results suggested that both tPA and plasma kallikrein-mediated uPA activation and tPA release contribute to endogenous fibrinolytic or thrombolytic mechanisms.

Animals↗

PubMed2002

Enhanced endogenous thrombolysis induced by a specific factor Xa inhibitor, DX-9065a, evaluated in a rat arterial thrombolysis model in vivo.

We have previously established an animal model to investigate mechanisms of arterial thrombolysis in vivo and have demonstrated that endogenous thrombolysis, mediated by thrombin-activatable fibrinolysis inhibitor, is enhanced by administration of specific thrombin inhibitors. The aim of the present study was to evaluate the effects of a synthetic and specific factor Xa inhibitor, DX-9065a, on endogenous fibrinolysis. Mural thrombi were formed in rat mesenteric arterioles by helium-neon laser irradiation in the presence of Evans blue. Thrombolysis was continuously monitored by video microscopy and was quantified using image analysis software. Oral and intravenous administration of DX-9065a enhanced endogenous thrombolysis in vivo. The mechanisms require additional investigation using other experimental systems, but nevertheless, the present results extended our previous findings and further suggested that the enhanced fibrinolysis might be due to depressed activity thrombin-activatable fibrinolysis inhibitor. The synthetic factor Xa inhibitor could provide the basis for a useful thrombolytic agent.

Administration, Oral↗

PubMed2002

Effects of Ginkgo biloba extract (EGb 761) on cerebral thrombosis and blood pressure in stroke-prone spontaneously hypertensive rats.

1. An extract of Ginkgo biloba (EGb 761) has been reported to alleviate cerebrovascular problems. In the present study, we investigated the antithrombotic effects of EGb 761 in cerebral blood vessels of stroke-prone spontaneously hypertensive rats (SHRSP/Izm). 2. In the present study, EGb 761 was administered orally to SHRSP/Izm at 60 and 120 mg/kg each day for 3 weeks from the age of 7 weeks. The age-related increase in blood pressure observed in SHRSP was suppressed significantly by EGb 761 at both doses 3 weeks after treatment. 3. Thrombotic potential was assessed in vivo using a He-Ne laser-induced thrombosis model and was significantly suppressed by EGb 761. 4. The anti-oxidant effects of EGb 761 were determined by measurement of urinary 8-hydroxy-2'-deoxyguanosine (8-OHdG). At 120 mg/kg, EGb 761 decreased 8-OHdG significantly compared with control animals. 5. Urinary nitrite/nitrate, nitric oxide (NO) metabolites, were increased significantly after administration of EGb 761. Expression of endothelial NO synthase (eNOS) mRNA was measured using a real-time quantitative reverse transcription-polymerase chain reaction method. The expression of eNOS mRNA in the EGb 761 group (120 mg/kg) was significantly higher than in the control group. 6. The results indicate that EGb 761 decreases blood pressure and mediates strong antithrombotic and anti-oxidant effects in SHRSP. These pharmacological activities may contribute to the beneficial properties of EGb 761 observed in clinical practice.

Animals↗

PubMed2002

Enhancement of endogenous plasminogen activator-induced thrombolysis by argatroban and APC and its control by TAFI, measured in an arterial thrombolysis model in vivo using rat mesenteric arterioles.

Recent in vitro studies have demonstrated that thrombin inhibits fibrinolysis through thrombin-activatable fibrinolysis inhibitor (TAFI, plasma procarboxypeptidase B). We have recently shown that endogenous fibrinolysis in vivo is enhanced by activated protein C (APC) and the selective thrombin inhibitor, argatroban. The aim of the present study was to examine the role of TAFI in these fibrinolytic mechanisms in vivo using purified porcine pancreatic carboxypeptidase B (PPCPB) and a specific TAFIa inhibitor, potato tuber carboxypeptidase B inhibitor (PTCI) in a newly established arterial thrombolysis model. Non-occlusive, mural, platelet-rich thrombi were formed by helium-neon laser irradiation in rat mesenteric arterioles and thrombus size was measured by computerised image analysis. We confirmed that endogenous thrombolysis was enhanced by argatroban (2.0 mg/4 ml/kg/h) or APC (1.62 mg/ 2.31 ml/kg). PTCI (5.0 mg/2 ml/kg) also accelerated endogenous thrombolysis. PPCPB (3.5 mg/2 ml/kg) inhibited thrombolysis in the absence and presence of argatroban or APC. PTCI tended to further promote APC-induced thrombolysis but the differences did not reach statistical significance. The present findings were in keeping with the results of earlier studies and demonstrated that arterial, platelet-rich thrombi in vivo are degraded by naturally generated plasminogen activators. TAFI may play a significant role in the control of these mechanisms.

Animals↗

PubMedDate not supplied

Platelet reactivity in spontaneously diabetic rats is independent from blood glucose and insulin levels.

Diabetes is associated with thrombotic disorders. Chemically induced and spontaneously induced diabetic animals and various in vitro tests have been used to reveal the prothrombotic state of diabetic patients. However, the results are not consistent. In the present study, platelet reactivity of spontaneously diabetic Goto-Kakizaki rats in vivo and in vitro was evaluated by laser-induced and shear-induced thrombosis models, which are physiologically relevant to thrombosis. Both results showed platelet hyperreactivity.

Animals↗

PubMedDate not supplied

Impaired flow-mediated vasodilation in vivo and reduced shear-induced platelet reactivity in vitro in response to nitric oxide in prothrombotic, stroke-prone spontaneously hypertensive rats.

Previous investigations using an He-Ne laser-induced thrombosis method have shown that stroke-prone spontaneously hypertensive rats (SHRSP) have an enhanced thrombotic tendency in vivo compared to normotensive, Wistar Kyoto rats (WKY). In addition, studies in the presence of acetylcholine have suggested the presence of endothelial dysfunction in SHRSP. In contrast, shear-induced platelet reactivity in vitro appeared to be depressed in SHRSP. The aim of the present study was to investigate endothelial function in SHRSP using a new physiological in vivo model, and to determine the response of platelets to nitric oxide (NO) in non-anticoagulated blood using a shear-induced platelet function in vitro method (haemostatometry). Endothelial function was estimated by measuring flow-mediated vasodilation (FMV) of the femoral artery. Vessels were exposed and blood flow was arrested using a silicone-coated arterial clamp. Vasodilation was measured by computer-assisted image analysis 3 min after release of stasis. Arterial vasodilation was observed in the femoral artery of WKY, but not in SHRSP. Vasodilation was seen in both WKY and SHRSP; however, in response to the NO donor, 1-hydroxy-2-oxo-3-(3-aminopropyl)-3-isopropyl-1-triazene (NOC 5). In contrast, 100 microM NOC 5 did not affect platelet reactivity in SHRSP. The NO scavenger, 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl 3-oxide, sodium salt (carboxy-PTIO) and the NO synthase inhibitor, N(G)-nitro-L-arginine methyl ester, hydrochloride (L-NAME), did not affect shear-induced platelet reactivity. NOC 5 at 10 microM (final concentration) inhibited shear-induced platelet reactivity in WKY. These results confirm the presence of endothelial dysfunction in SHRSP and indicate that platelets are non-responsive to NO in this hypertensive model. The data suggest that defective endothelial reactions or disturbed thrombogenic mechanisms outweigh the platelet hyporeactivity and contribute to the prothrombotic status in SHRSP.

Animals↗

PubMedDate not supplied

High intensity exercise enhances platelet reactivity to shear stress and coagulation during and after exercise.

Platelets play a crucial role in the pathogenesis of acute cardiac events, such as angina, myocardial infarction and sudden death. It is believed that regular low-intensity exercise can reduce, while high-intensity exercise may provoke acute cardiac events. The aim of the present study was to investigate the effect of acute exercise both at low and high intensities on the ventilatory threshold (VT), platelet reactivity and coagulation before and after exercise. Platelet reactivity and coagulation were measured under flow condition, using native blood, by hemostatometry. Seven healthy young men (age: 20-29 years) performed bicycle ergometer exercise for 30 min at intensities of 90% (Ex-VT90% or approximately 55% VO(2max)) and 130% (Ex-VT130% or 80% VO(2max)) of individual VT. Blood cell counts, hematocrit, blood lactic acid and plasma catecholamine levels were slightly but significantly increased after Ex-VT90% and markedly after Ex-VT130% after 30 min exercise. Subsequent to the exercise, the elevated blood cell counts decreased to the resting levels both at Ex-VT90% and at Ex-VT130%. Platelet reactivity to shear stress and dynamic coagulation were significantly enhanced immediately and 30 min after Ex-130%VT. In contrast, no significant changes occurred in those of Ex-90%VT. The present study suggests that high-intensity exercise-induced platelet hyperreactivity and hypercoagulable state may pose an increased risk for acute, sometimes fatal cardiac event. On the other hand, our findings support the view that low-intensity exercise does not present a risk of thrombosis.

Adult↗