Is the antithrombotic activity of "antiplatelet" drugs based on protection of endothelium?

In only five "antiplatelet" agents has the antithrombotic activity been confirmed both clinically and experimentally. These include acetylsalicylic acid, dipyridamole, clofibrate, hydroxychloroquine and sulfinpyrazone. Whereas only acetylsalicylic acid has a demonstrable effect on platelet aggregation in doses usually applied, the effects of all remaining drugs are more easily explained by their influence on the vessel wall. This assumption is supported by the finding that all five drugs possess a stabilizing effect on endothelium in doses corresponding closely to the clinical dose range. The method based on counting detached endothelial cells in blood after a standard stimulus was used to demonstrate this effect.

A sensitive model of venous thrombosis in rats.

Several antithrombotics (heparin, acetylsalicylic acid, sulfinpyrazone and dipyridamole) as well as an antiserotonin ketanserin were tested in a new sensitive model of venous thrombosis in rats. Intravenous injection of hypotonic saline was used for thrombus induction combined with the vena cava ligation. Formation of thrombi was evaluated by their weights. With i.v. heparin, oral sulfinpyrazone and acetylsalicylic acid, i.v. dipyridamole and ketanserin an effective inhibition was obtained, whereas with oral dipyridamole and ketanserin the inhibition remained incomplete.

Antithrombotics in view of thrombosis models.

Two highly sensitive models of arterial and venous thrombosis forming with the test of endothelial stability a complementary system with a maximum stress on the role of vascular lesion were used to test a series of four antithrombotic drugs (heparin, acetylsalicylic acid, dipyridamole, sulfinpyrazone) and four drugs with other indications but with an antithrombotic activity in experiment (prenylamine, troxerutin, ketanserin and pizotifen). All drugs, except heparin, were given orally. Whereas heparin, aspirin and prenylamine had mixed effects on both arterial thrombosis (i.e. mostly on platelet functions) as well as on endothelial stability, ketanserin and pizotifen had a predominant effect on the former while dipyridamole, troxerutin and sulfinpyrazone influenced mostly the latter function.

A new model of arterial thrombosis.

A new model of arterial thrombosis in rats was based on a combination of a localizing hemodynamic factor /partial mechanical constriction of aorta/, generalized mild endothelial lesion /i.v.hypotonic saline/ and a humoral factor/i.v. serotonin/. The resulting aortic occlusion was indicated by measuring rectal temperature. Nicotine and oral methionine were similarly active as hypotonic saline. Histamine had to some extent similar activity as serotonin. The possible contribution of serotonin vasoactivity to the vascular obstruction was contradicted.

The effect of antithrombotics in a new model of arterial thrombosis.

A series of drugs representing several groups of antithrombotics was tested in a new model of arterial thrombosis in rats. Thrombosis was produced in the aorta by the combination of local partial obstruction and systemic administration of hypotonic saline with serotonin. High efficacy was demonstrated with heparin, acetylsalicylic acid, troxerutin, prenylamine, antiserotonin agents /pizotifen, ketanserin/ and particularly with the combinations of antiserotonins and the above mentioned antithrombotic drugs. The model showed high sensitivity to all tested drugs in the clinical dose range.

The effect of heparin on endothelial stability.

Heparin in ultra low doses had a stabilizing effect on endothelial lining in rats. This effect was demonstrated as prevention of increases in counts of circulating endothelial cells after a standard intravenous citrate injection. The same effect of heparin was observed even with other provoking agents /adrenaline, hypotonic saline/. The duration of heparin effect was very prolonged, a 50% effect having been observed 5 hours after the administration. Subcutaneous heparin was effective only in relatively high doses and had a lower maximum effect compared with intravenous heparin.

Experimental model of thrombus adherence to the vessel wall.

Clot adherence to peritoneal cavity mesothelium was studied in rats in an attempt to contribute to the problem of thrombus embolization. The adherence was decreased by platelets and the active constituent was identified as adenosine diphosphate which decreased the sticking of fibrin to cellular linings as well as to artificial surfaces.

Heparan sulfate as a venostatic endothelial stabilizing factor.

A humoral transfer of a factor inducing a decrease of circulating endothelial cells (CEC) released during venostasis was demonstrated in rats. The possibility to block its activity by an in-vitro addition of protamine suggests its identity with an endogenous heparan sulfate possessing an inhibitory effect on endothelial turnover. This was supported by an analogous effect of intravenously administered heparan sulfate-related agent.

Antithrombotic activity of an unsaturated fatty acid preparation.

An unsaturated fatty acid preparation from fish oil, "Epavit", completely prevented arterial thrombosis induced in the rat aorta by a combined stenosis, extensive endothelial perturbation and i.v. serotonin, at an optimum dose of 0.1 ml/200 g orally. A partial effect lasted more than 18 hours. After repeated administrations the acute completely inhibitory effect was decreased but the partial and chronic one remained unchanged. Aspirin (ASA) showed no synergic activity. Venous thrombosis (one-sided ligature of the caval vein combined with extensive endothelial perturbation) was inhibited to a similar degree as arterial thrombosis. Epavit also prevented the destabilizing effect of i.v. citrate on the endothelial lining.

Homocysteinemia and endothelial damage after methionine load.

Homocysteinemia increased significantly after a methionine load of 50 mg/kg in patients with peripheral artery occlusive disease but this load was insufficient to increase circulating endothelial cell count as a marker of endothelial damage. Only after an increased load of 100 mg/kg methionine circulating endothelial cells also increased markedly confirming the results of a previous experimental study. These data indicate a threshold concentration of homocysteine in blood necessary to induce endothelial lesions.

Lack of evidence for the interaction between renin-angiotensin-aldosterone system and endothelin in vivo.

Aim of the study was to reveal the possible factors regulating plasma endothelin (ET) levels in vivo in patients with essential hypertension (EH) by the simultaneous determination of plasma renin activity (PRA) and plasma aldosterone (ALD). In addition, the possible relationship between ET and circulating endothelial cells as a marker of endothelial damage was also investigated. The postural test revealed a significant increase of ET levels (26.7 +/- 9 vs 11.5 +/- 3 fmol/ml, p < 0.05) in the upright position. Captopril administration did not change plasma ET levels. No significant correlation was found between ET and PRA or ALD. Although a tendency to a positive correlation between ET and circulating endothelial cells (as the marker of endothelial perturbation) was found, it did not attain statistical significance. Our data do not support the suggestion that the renin-angiotensin-aldosterone system plays a major role in the regulation of ET secretion in vivo in EH. Postural stimulation of ET secretion may be caused by other factors than renin-angiotensin-aldosterone system.

Protection by flunarizine against endothelial cell injury in vivo.

Flunarizine in vivo protects against endothelial cell damage induced by intravenous injection of citrate, CaCl2, or lactate in rats. Its effect is optimal at the low oral dose of 0.1 mg/kg, corresponding to the clinically used one. It lasts for at least 8 hours. Edema formation, platelet activation, and venostatic thrombosis subsequent to endothelial cell injury consequently are also inhibited by flunarizine. The compound does not affect platelet function, plasma coagulation or generation of PGI2 by vascular tissue and does not impair normal haemostasis at effective doses. As for its vascular and hemorrheological effects, the protection by flunarizine against endothelial injury may be related to its Ca2+-antagonistic properties.

Oral contraceptives, methionine and endothelial lesion.

PIP: Estrogen (mestranol), 1 mcg/kg administered for 1 week decreased the tolerance of rats for methionine, and women aged 20-30 years were prescribed oral contraceptives (OCs) after passing the methionine tolerance tests. The OCs prescribed for women were 0.25 and 1 mg cholersuperlutin combined with 0.08 mg mestranol. In 1 group this OC was combined with pyridoxine 120 mg daily in capsules. The study in rats showed oral administration of methionine 50 mg/kg to have no effect on endothelaemia counts. Tolerance for the same dose of methionine markedly decreased in animals treated for 1 week with with an estrogen preparation of mestranol 1 mcg/kg orally. The effect of estrogen treatment on methionine tolerance was completely prevented by simultaneous daily administration of pyridoxine 10 mg/kg. In women the results were expressed in terms of endothelaemia counts before and after the period of contraceptive treatment. In another group of women the OC was administered together with pyridoxine 120 mg daily for the same time period and no significant change in methionine tolerance was observed. The decreased tolerance in women was prevented by administration of OCs in combination with pyridoxine.^ieng

[Lipoperoxides and atherosclerosis]. / Lipoperoxidy a ateroskleróza.

The theory of the pathogenetic role of lipoperoxides in atherosclerosis and thrombosis is very topical at present. It unifies the theory on the role of free oxygen radicals with the theory of damage of the vascular wall and with the theory of impaired lipid metabolism. It makes possible also a new interpretation of known risk factors. It is also based on the most recent results of molecular biology (role of monocytes-macrophages).

[The antiphospholipid syndrome and atherothrombosis]. / Antifosfolipidový syndrom a aterotrombóza.

The antiphospholipid antibody syndrome is an autoimmune disease which attracts in recent years increasingly the attention of angiologists and cardiologists. Although it is manifested as regards laboratory indicators as a circulating anticoagulant, somewhat paradoxically clinicians observe only a marked tendency towards venous and arterial thromboses at different sites. The condition is frequently encountered in young people with idiopathic and recurrent diseases. Laboratory diagnosis of the condition as well as new therapeutic possibilities are being developed.

[Heparan sulfate and its function in the endothelium]. / Heparansulfát a jeho funkce v endotelu.

The author presents an account of the main contemporary findings on the functional importance of heparan sulphate (HS), which is an important part of the endothelial glycocalyx. Based on the ability to form complexes with proteins, HS interferes in particular with antithrombotic properties of the endothelium and modulates in a significant way the proliferative activity of the endothelium and other cells of the vascular wall. The author mentions its pathogenetic role, possibilities of its diagnostic use and therapeutic perspectives in the area of vascular diseases.

[Electric conductivity of erythrocyte sediments and red blood cell deformability]. / Elektrická vodivost erytrocytárního sedimentu a deformabilita cervených krvinek.

BACKGROUND: To assess the deformability of erythrocytes several methods can be used. The latter investigate either the properties of single blood cell or the properties of a red cell suspension. The objective of the present study was to assess whether experimentally induced deterioration of the red cell deformability can be recorded by measurements of the electric conduction of red cell sediment. METHODS AND RESULTS: In ten patients with disorders of the circulation 10 ml blood samples were taken, mixed with a solution of sodium citrate and centrifuged at 1250 g for 10 minutes. The separated blood cells were repeatedly centrifuged and rinsed. Red cell deformability was experimentally enhanced by incubation of erythrocytes in a Ringer-albumin solution. The change of deformability was detected by viscosimetry and assessment of the electric conduction of the red cell sediment, using a conductometer Radelkis 101 OK, the temperature of the sediment being 10 degrees C. The viscosity values of red cell suspensions with a haematocrit of 0.45 were assessed at six shear rates and they were in all instances higher after incubation of red cell suspensions, as compared with the viscosity of suspensions of fresh erythrocytes. The mean value of electric conduction of the sediment with a haematocrit of 0.45 before incubation was 0.132 mS and after 24 hours incubation 0.218 mS; the difference was statistically significant (p < 0.0005). CONCLUSIONS: Deterioration of red cell deformability is associated with improved electric conduction of the red cell suspension of sediment. It is possible to use assessment of electric conduction of the red cell sediment to assess erythrocyte deformability. The method is simple and cheap, as compared with the viscosimetric method.

[Lipoperoxides and their clinical importance]. / Lipoperoxidy a jejich klinický význam.

BACKGROUND: Research and investigations in the sphere of lipid peroxides has been pursued so far for a relatively short time. Therefore every new finding is a great asset for this branch of medicine. An elevated lipid peroxide level signalizes pathological changes in the organism. Malondialdehyde is an indicator of lipid peroxidation. The authors focused their experimental work on assessment of malondialdehyde in human serum. They tested the effect of increased radical peroxidation caused by diabetes and investigated whether it raises the lipid peroxide level in a group of patients suffering from ischaemic heart disease. METHODS AND RESULTS: Two groups were formed--one comprising 10 patients with ischaemic heart disease and another one of 8 patients with ischaemic heart disease and type II diabetes. The malondialdehyde concentrations were moreover compared with a control group of healthy subjects. The mean age of the first group was 72 years, of the second group 69 years. The mean age of the control group was 64 years. Lipid peroxidation was assessed from the concentration of malondialdehyde using an analytical method--spectrophotometry with fluorescence detection. CONCLUSIONS: Statistical evaluation of lipid peroxide levels in the two groups of patients with ischaemic heart disease led to the conclusion that the differences were not significant. Type II diabetes did not cause a greater increase of lipid peroxides in patients with IHD.