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Biomedical subjects

F Markwardt

Publications and source records attributed to F Markwardt.

At least 91 records · Page 5Linked to original sources
PubMed1988

Inhibitory effect of hirudin on thrombosis induced by prothrombin complex concentrates.

The influence of hirudin on thrombus formation induced by prothrombin complex concentrate (PCC) was studied in two different test series in rats. Within the first test series hirudin was i.v. administered to the animals 10 min before they received PCC. Complete prevention of thrombus formation required a hirudin dose of 0.2 mg/kg. Within the second test series hirudin was added to the transfusion unit of PCC before application of PCC was started. In this case complete prevention of thrombus formation was yielded by addition of 140 micrograms hirudin to the PCC transfusion unit. In comparison with heparin and the synthetic thrombin inhibitor N alpha-(2-naphthylsulfonyl-glycyl)-4-amidinophenylalanine piperidide, hirudin was most potent.

Animals↗
PubMed1988

Clinical use of hirudin.

The pharmacokinetics and the effects on the haemostatic system of hirudin were assessed in healthy volunteers after single doses of 1,000 AT-U/kg administered intravenously respectively subcutaneously. First clinical experiences on hirudin treatment in chronic DIC are reported.

Adult↗
PubMed1988

Experimental studies on the antithrombotic and haemorrhagic effects of heparin and a low molecular weight heparin derivative.

Antithrombotic, haemorrhagic and anticoagulant effects of unfractionated heparin (UH) and the low molecular weight heparin fragment KABI 2165 were studied in rats. In stasis-induced venous thrombosis of the jugular vein intravenous injection of both, UH and KABI 2165, either reduced significantly the size of thrombi or completely prevented thrombus formation in a dose-dependent manner. The dose of KABI 2165 required for prevention of thrombus formation showed a marked anticoagulant activity measured by APTT which was in the same range as that of the equieffective dose of UH. After administration of antithrombotically effective doses only UH caused a significant prolongation of bleeding time after standardized incision of the tail. KABI 2165 produced haemorrhagic effects at about 4-fold higher doses only than those required for the antithrombotic action.

Animals↗
PubMed1988

Antithrombotic and haemorrhagic effects of the naturally occurring thrombin inhibitor hirudin.

Haemorrhagic effects of the naturally occurring thrombin inhibitor hirudin measured by the determination of bleeding time were compared with its antithrombotic actions in different models of experimental thrombosis. In mice and rats intravenous administration of hirudin caused a plasma concentration-dependent prolongation of bleeding time after transection of the tail tip and standardized incision of the tail, respectively. In rats intravenous infusion of hirudin prevented the formation of stasis-induced venous thrombosis of the jugular vein and the occurrence of thrombotic occlusion of the carotid artery after electrically induced damage of the vessel wall. Comparison of the haemorrhagic action of hirudin with its antithrombotic effectiveness showed that it caused haemorrhagic side effects only at plasma concentrations which are not required for the antithrombotic effects.

Animals↗
PubMed1988

Prevention of experimental coronary thrombosis by hirudin.

The antithrombotic activity of hirudin was studied in a rat coronary thrombosis model. The thrombus formation was induced by external application of silver nitrate solution onto the left anterior descending coronary artery. Following subcutaneous injection, hirudin in doses of 0.25, 0.5 and 1.0 mg/kg reduced the development of coronary thrombosis in a dose-dependent manner. The most pronounced antithrombotic effect of hirudin in the described model was related with plasma concentrations between 0.20 and 0.35 microgram hirudin/ml.

Animals↗
PubMed1988

Evidence for the identity of hirudin isolated after kidney passage with the starting material.

Natural, sulfated and recombinant, non-sulfated hirudin preparations re-isolated from urine after kidney passage were compared with the corresponding administered preparations by reversed-phase high-performance liquid chromatography, and by amino acid sequence and composition analysis. It could be demonstrated that the hirudins were excreted in unmodified form. Natural hirudin could be fractionated by the chromatographic system used into a large number of isoinhibitor forms, some of which were shown to differ from each other in their amino acid sequence.

Amino Acid Sequence↗
PubMed1988

Pharmacokinetic studies with recombinant hirudin in dogs.

The knowledge of the pharmacokinetics of recombinant hirudin is essential for potential clinical use of this selective thrombin inhibitor. For detailed information about absorption, distribution and elimination, pharmacokinetic studies with recombinant hirudin were carried out in dogs. The plasma concentration time curve after intravenous injection could be best described by an open two-compartment model with first order kinetics. The subcutaneous application of recombinant hirudin produced anticoagulantly effective blood level for a prolonged period of time. Recombinant hirudin is distributed into the extracellular space. This is also found in nephrectomized dogs. Recombinant hirudin is eliminated through the kidneys by glomerular filtration in active form with a half-life of 72 minutes.

Animals↗
PubMed1988

[Synthesis of N-alpha-(arylsulfonyl)-4-amidino-phenylalanyl-prolines and N-alpha-(arylsulfonylglycyl)-4-amidino-phenylalanyl-prolines and testing of them as inhibitors of serine proteinases. 33. Synthetic inhibitors of serine proteinases].

The headline compounds were prepared by the reaction of N alpha-(arylsulfonyl)- and N alpha-(arylsulfonylglycyl)-4-cyanophenylalanines to the L- and D-proline derivatives. These compounds were transformed in a usual manner in the amidino compounds. The substitution of the pyrrolidine residue by L-proline in this type of inhibitors decreased the activity against serine proteases, especially against thrombin. In the case of the D-proline derivatives the decrease of the inhibitor activity against thrombin was very high.

Chemical Phenomena↗
PubMed1988

Pharmacology of selective thrombin inhibitors.

Thrombin plays a key role in thrombosis and haemostasis, and is selectively inhibited by hirudin and synthetic inhibitors. Hirudin, a polypeptide (molecular weight 7,000 daltons) extracted from medicinal leeches, can now be produced by gene technology. Hirudin binds selectively to thrombin with high affinity and inhibits its enzymatic properties. Besides heparin, hirudin is not inhibited by platelet factor 4; it prolongs in vitro and ex vivo routine blood coagulation assays and prevents thrombosis in a number of animal models without increasing haemorrhagic risk. In humans, hirudin disappears from the blood with a half-life of 1 h, is devoid of undesirable side effects and has been shown to be efficient in the treatment of chronic disseminated intravascular coagulation (DIC). A number of synthetic direct thrombin inhibitors have been described, including benzamidine derivatives which share identical pharmacological properties with hirudin; however their biological half-life after i.v. injection is shorter. Other derivatives (amidino-phenyl-pyruvic acid) have longer half-lives and have been used to treat chronic DIC in man.

Animals↗
PubMed1988

Studies on thrombin-induced endothelium-dependent vascular effects.

The clotting enzyme thrombin induces not only blood coagulation but it also receptor-mediated cellular events. In our studies, thrombin at nanomolar concentrations caused irreversible aggregation of washed human platelets which was inhibited by the naturally occurring tight-binding inhibitor hirudin. Thrombin within the same concentration range caused concentration-dependent transient relaxation of PGF2 alpha-precontracted pig coronary artery ring segments with intact endothelium. The relaxant response was neither affected by indomethacin nor by verapamil and was only slightly inhibited by exposure to calcium-free medium. Methylene blue enhanced the PGF2 alpha-induced contraction and diminished the thrombin-induced relaxation. Hirudin inhibited the relaxant effect of thrombin in a concentration-dependent manner. After removal of the endothelium by mechanical rubbing the thrombin-induced relaxation was absent. The present studies suggest that thrombin generated during coagulation is able to modify the vascular smooth muscle tone.

Animals↗
PubMed1988

Influence of velocity, temporal frequency and initial phase position of grating patterns on motion VEP.

The cortical potential visually evoked by motion of a periodic grating (motion VEP) is composed of a transient component which decays within 500 ms of stimulus-onset (motion-on VEP) and a sustained component. Amplitude and peak latency of wave N2 of the motion-on VEP are functions of grating velocity. Both remain constant at spatial frequencies between 0.6 and 4.3 c/deg and at temporal frequencies within the equivalent intervals. The transient component of the motion VEP is independent of the spatial phase position of the grating before motion onset. The sustained component can only be seen in the averaged motion VEP at constant phase position of the grating before motion onset. This potential consists of periodical fluctuations with a main frequency equal to the temporal frequency of the moving grating. As a result of psychophysical investigations some authors suggest pattern velocity is the relevant variable of velocity perception, others temporal frequency. The motion VEP is dependent on both velocity and temporal frequency, the transient component is a function of velocity, the sustained component of temporal frequency.

Electroencephalography↗
PubMed1988

[Synthetic inhibitors of serine proteinases. 34. The effect of modification of the amidino function of N-alpha-substituted 4-amidinophenylalanine amides on inhibitory activity].

Cyclic amides of N alpha-arylsulfonylated 4-amidinophenylalanine are selective inhibitors of thrombin. The exchange of the amidino function for an aminomethyl residue does not influence the selectivity and potency of their inhibitory activity. In contrast, the modification of the amidino function of the N alpha-arylsulfonylaminoacylated compound N alpha-(2-naphthylsulfonylglycyl)-4-amidinophenylalanine piperidide results in a drastic loss of inhibitory activity. Only the oxamidino derivative possesses considerable high affinity for thrombin. Obviously, in tight binding inhibitors of thrombin structural variation results in any case in a loss of inhibitory activity.

Amidines↗
PubMed1988

Pharmacological survey of recombinant hirudin.

The pharmacological properties of a genetically engineered recombinant hirudin (r-hirudin) were studied in animal experiments. r-Hirudin proved to be a well tolerated substance. I.v. injection of up to 200 mg/kg did not lead to perceptible functional or morphological changes. There were no treatment-related effects on the cardiovascular system of dogs and rats after administration of up to 10 mg/kg. After long-term treatment (4 weeks, 1.0 mg/kg daily), no r-hirudin-related histopathological, haematological or biochemical changes could be found. Formation of antibodies was not detectable. Absorption, distribution, and elimination of r-hirudin were studied in dogs and rats. Pharmacokinetics could be best described by an open two-compartment model with first-order kinetics. After i.v. injection in dogs, r-hirudin is distributed into the extracellular space and eliminated through the kidneys in active form by glomerular filtration. After i.v. administration, a half-life of about 1 h was estimated; s.c. administration prolonged the apparent half-life. Pulmonary absorption was shown. Enteral absorption, placental transfer as well as transfer through the fetal integument were very low. r-Hirudin did not pass the blood-brain barrier. The efficacy of r-hirudin in preventing both venous and arterial thrombosis, vascular shunt occlusion or disseminated intravascular coagulation was demonstrated in rats. Depending on the dose, r-hirudin was able to prevent or reduce stasis-induced venous thrombosis, prolong the patency of an extracorporeal arteriovenous shunt, reduce the incidence of arterial thrombosis caused by vascular wall lesions as well as of microthrombosis induced by thrombin infusion.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1987

[Pharmacologic principles of fibrinolytic therapy].

Increasing insight into the mechanisms of fibrinolysis, and particularly into the formation and release of plasminogen activator, has led to more effective thrombolytic therapy. The understanding of the mechanism of thrombolysis has provided the possibility to improve the therapeutic effects of the fibrinolytic agents streptokinase and urokinase. Further advances in thrombolytic therapy are expected by the use of the plasminogen activator from endothelium and pro-urokinase. Acylation of fibrinolytic enzymes will lead to beneficial effects (depot effect, protection from intrinsic inhibitors). Due to the extensive research into substances with fibrinolytic and thrombolytic effects a new generation of activators of fibrinolysis is expected that interferes with the biosynthesis and release of plasminogen activator of the vessel wall and that is suited for treatment of hypofibrinolytic states.

Blood Coagulation↗