Responses of canine jugular veins and carotid arteries to hysterectomy: increased permeability and leukocyte adhesions and invasion

Inhibitory effects of ethanol extract from Radix Ophiopogon japonicus on venous thrombosis linked with its endothelium-protective and anti-adhesive activities

The in-vivo inhibitory effects of the ethanol extract of Radix Ophiopogon japonicus (ROJ-ext) on venous thrombosis were studied in mouse and rat models and in-vitro endothelial cell-protective and anti-adhesive activities were observed in ECV304 cells injured by sodium dithionite and HL-60 adhesion to ECV304 cells injured by TNF-alpha. The in-vivo results showed that ROJ-ext significantly inhibited venous thrombosis induced by tight ligation of the inferior vena cava for 6 h in mice and for 24 h in rats by once oral administration at doses of 12.5 and 25 mg/kg. Meanwhile, ROJ-ext had no obvious effect on some coagulation parameters, which was different from warfarin, which remarkably prolonged activated partial thromboplastin time (APTT), thrombin time (TT) and prothrombin time (PT) in rats at the same time. Histological analysis under light microscope and scanning electron microscope (SEM) of inferior vena cava indicated that ROJ-ext could protect endothelial cells from anoxic injury and alleviate inflammatory changes in the vein wall. On the other hand, the in-vitro studies approved that ROJ-ext significantly enhanced viability of ECV304 cells injured by sodium dithionite at the concentrations of 0.1, 1.0 and 10 mug/ml when given before and after the anoxic induction. Meanwhile, ROJ-ext remarkably inhibited adhesion of HL-60 cells to ECV304 cells injured by rh TNF-alpha at above concentrations in a dose-dependent manner. The findings of this study showed that ethanol extract of Radix Ophiopogon japonicus (ROJ-ext) inhibited venous thrombosis, which linked with its endothelial cell-protective and anti-adhesive activities. This lends scientific support to the therapeutic use of the plant for thrombotic diseases.

P-Selectin-dependent inhibition of thrombosis during venous stasis

Leukocyte adhesion, transendothelial migration, and stasis are important components in the pathogenesis of deep vein thrombosis. Anesthetized cats were treated with saline, a recombinant soluble form of P-selectin glycoprotein ligand-1 (rPSGL-Ig), or an E- and L-selectin antibody (EL-246) before exposure and occlusion of a jugular vein. After 2 or 6 hours of occlusion, jugular veins were perfused with buffer, fixed, and prepared for scanning electron microscopy. In cats receiving saline, 2 and 6 hours of occlusion produced moderate levels of leukocyte and platelet adhesion and endothelial cell injury. Treatment of cats with rPSGL-Ig or EL-246 had no apparent effect on the magnitude of cell adhesion and endothelial cell injury compared with no treatment. After 6 hours of occlusion, the presence of a mural thrombus in untreated veins was observed and confirmed by scanning electron microscopy. Pretreatment of cats with rPSGL-Ig completely (4.0 mg/kg) or partially (1.0 mg/kg) prevented the occurrence of thrombi in the jugular veins. The reduction in thrombosis by rPSGL-Ig treatment after 6 hours of venous stasis, in the absence of any effect on leukocyte-mediated endothelial cell injury, suggests an antithrombotic mechanism of action for this protein.

Occlusive vascular diseases in oral contraceptive users. Epidemiology, pathology and mechanisms

Despite being an unprecedented departure from normal physiology, the combined oral contraceptive is not only highly effective, but it also has a remarkably good safety record. Concerns over safety persist, though, particularly with regard to venous thromboembolism (VTE), stroke and myocardial infarction (MI). Epidemiological studies consistently show an increase in risk of VTE, but the results are more contentious with regard to arterial diseases. Despite 40 years of research, the mechanisms behind these adverse effects are not understood. In this review, we integrate information from published studies of the epidemiology and pathology of the occlusive vascular diseases and their risk factors to identify likely explanations for pathogenesis in oral contraceptive users. Oral contraceptives induce both prothrombotic and fibrinolytic changes in haemostatic factors and an imbalance in haemostasis is likely to be important in oral contraceptive-induced VTE. The complexity of the changes involved and the difficulty of ascribing clinical significance has meant that uncertainty persists. A seriously under-researched area concerns vascular changes in oral contraceptive users. Histologically, endothelial and intimal proliferation have been identified in women exposed to high plasma estrogen concentrations and these lesions are associated with thrombotic occlusion. Other structural changes may result in increased vascular permeability, loss of vascular tone and venous stasis. With regard to arterial disease risk, epidemiological information relating to dose effects and joint effects with other risk factors, and studies of pathology and changes in risk factors, suggests that oral contraceptive use per se does not cause arterial disease. It can, nevertheless, synergise very powerfully with subclinical endothelial damage to promote arterial occlusion. Accordingly, the prothrombotic effects of the oral contraceptive estrogen intervene in a cycle of endothelial damage and repair which would otherwise remain clinically silent or would ultimately progress - in, for example, the presence of cigarette smoking or hypertension - to atherosclerosis. Future work in this area should focus on modification of the effects of established risk factors by oral contraceptive use rather than modification of the supposed risk of oral contraceptive use by established risk factors. Attempts to understand vascular occlusion in oral contraceptive users in terms of the general features of VTE or with reference to atherosclerosis may be limiting, and future work needs to acknowledge that such occlusions may have unique features. Unequivocal identification of the mechanisms involved would contribute considerably to the alleviation of fears over vascular disease and to the development of even safer formulations.

The relationship between vessel wall injury and venous thrombosis: an experimental study

The relative importance of stasis, vessel wall damage and hypercoagulability in the pathogenesis of venous thrombosis remains disputed. While the combination of local vascular stasis and systemic hypercoagulability can be shown to produce experimental thrombi within a few minutes, it has been claimed that vessel wall damage is also a necessary component of venous thrombogenesis. In this experimental study, mechanical crushing of the jugular veins produced patchy areas of denuded endothelium, with underlying vessel wall oedema, as seen by ultrastructural examination. While the exposed subendothelium became covered with activated platelets following restored blood flow, there was no fibrin formation after 5 min. When blood flow was restored for 60 min following the crush injury, white cells could be seen adhering to and migrating through the vessel wall, although there was still no visible fibrin. The addition of venous stasis for 20 min did not lead to the formation of stasis thrombi in association with the damaged areas. The present experiments demonstrate that, far from there being subtle endothelial damage contributing to acute venous thrombosis, even readily demonstrable damage is a poor stimulus to fibrin formation at local sites of vessel wall injury.

The effect of stasis on the venous endothelium: an ultrastructural study

In carefully dissected neck veins, no evidence was found of platelet adherence to the vessel wall or leucocyte migration. However, 30-60 min of total stasis led to polymorphonuclear leucocytes sticking to the endothelium and their subsequent migration. This migration across the vessel wall resulted from stasis and not the trauma of dissection. Adherence and migration of leucocytes did not cause gross endothelial cell damage or desquamation within the observed period of stasis and there was no associated platelet adherence following restoration of blood flow. Thus leucocyte migration does not impair the non-thrombogenicity of the endothelium in acute experiments.