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Biomedical subjects

A Bernat

Publications and source records attributed to A Bernat.

66 records · Page 4Linked to original sources
PubMed1989

Point mutations modifying the thrombin inhibition kinetics and antithrombotic activity in vivo of recombinant hirudin.

The hirudin variant HV2 was modified by in vitro site-specific mutagenesis of HV2 cDNA to generate HV2(Asn-47----Lys), HV2(Asn-47----Arg) and HV2(Lys-35----Thr, Asn-47----Lys). Residues 35 and 47 are positioned respectively within the finger and prothrombin-like domains of hirudin, both of which have been suggested as thrombin binding sites. The modified polypeptides were synthesized in Saccharomyces cerevisiae using a secretion vector and purified from culture supernatants. By analysis of the human alpha-thrombin:hirudin inhibition reaction in steady-state conditions it was shown that the dissociation constants for HV2(Lys-47) and HV2(Arg-47) were 5- to 14-fold lower than for unmodified HV2, whereas mutation of Lys-35 did not significantly alter the inhibition kinetics. Furthermore, HV2(Lys-47), whose sequence is identical to a natural hirudin variant, displayed enhanced anti-thrombotic activity in vivo, having a 100-fold lower ED50 compared to HV2 in the rabbit Wessler venous thrombosis model. These results support a role for the prothrombin-like domain in thrombin binding and, moreover, demonstrate that in vivo antithrombotic efficiency correlates with the dissociation constant of the inhibition reaction.

Amino Acid Sequence↗
PubMed1988

ADP plays a key role in thrombogenesis in rats.

The relative importance of ADP, arachidonic acid metabolites and serotonin as thrombogenic factors was evaluated in rats by comparing, after oral administration, the effects of two inhibitors of ADP-induced platelet aggregation (ticlopidine and PCR 4099), three cyclo-oxygenase inhibitors (aspirin, triflusal and indobufen) and a selective serotonin 5HT2 receptor antagonist (ketanserin) on platelet aggregation, in four platelet-dependent thrombosis models and on bleeding time. Platelet aggregation induced by ADP and collagen was completely inhibited by ticlopidine and PCR 4099 whereas only the collagen aggregation was reduced by the cyclo-oxygenase inhibitors. Ketanserin or a depletion of platelet serotonin by reserpine did not affect platelet aggregation. Ticlopidine and PCR 4099 greatly prolonged rat tail transection bleeding time. This is probably related to their known ability to inhibit ADP-mediated platelet aggregation. In contrast, the cyclooxygenase inhibitors did not affect bleeding time at all. Reserpine and ketanserin prolonged bleeding time by interfering with the action of serotonin on the vascular wall. Ticlopidine and PCR 4099 were very potent antithrombotics in all the models. Aspirin, only at a high dose, inhibited poorly thrombus formation on a silk thread in an arterio-venous shunt, suggesting that the inhibition of cyclo-oxygenase was not responsible. Triflusal was inactive in all models while indobufen slightly reduced thrombus formation in the silk thread and metallic coil models. Ketanserin and reserpine reduced thrombus only in the metallic coil model. Thrombus formation was greatly reduced in fawn-hooded rats, which lack ADP in their platelet dense granules because of a genetic storage pool deficiency.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenosine Diphosphate↗
PubMed1987

Antithrombotic and bleeding effects of a new synthetic direct thrombin inhibitor and of standard heparin in the rabbit.

This study reports on the anticoagulant, antithrombotic and bleeding effects of a new synthetic direct thrombin inhibitor (SDTI) in comparison with standard heparin (SH). The anticoagulant effect was determined with the thrombin clotting time (TCT) and the activated partial thromboplastin time (APTT). SDTI was more potent than SH in prolonging the TCT, but as potent as SH in prolonging the APTT. The antithrombotic effect was determined using a modified Wessler model in the rabbit, either 30 min after a continuous IV infusion of increasing doses or at various times after a single SC injection (20 mg/kg). After continuous IV infusion of 187 micrograms/kg/h of SDTI and of 60 micrograms/kg/h of SH, significant thrombus prevention effects were obtained (59 and 57% respectively). Increasing the dose of SDTI up to 3000 micrograms/kg/h did not significantly improve the antithrombotic effect. After SC injection, a significant antithrombotic effect was observed for 12 h with SDTI but for more than 24 h with SH. The bleeding effect was studied using the rabbit ear model 15 min after a continuous infusion of 7.5 and 15 mg/kg/h: the amounts of blood loss were dose-dependent and comparable for SDTI and SH. These studies also indicated that SDTI possesses a considerable shorter half-life in comparison with SH. Accordingly, the ex vivo concentrations generated after continuous IV infusion or SC injection of the same dose were higher for SH than for the SDTI.

Animals↗
PubMed1985

Antithrombotic effect of ticlopidine in a platelet-independent model of venous thrombosis.

The antithrombotic activity of ticlopidine demonstrated in a variety of experimental models of thrombosis has been explained by its antiaggregating properties. This study describes the antithrombotic effect of ticlopidine in a platelet independent model of venous thrombosis. In the rat, ligature of the inferior vena cava induces thrombosis. Antiaggregating drugs (acetylsalicylic acid, dipyridamole, sulfinpyrazone) are inactive while anticoagulants (heparin, acenocoumarol) are highly antithrombotic. Ticlopidine reduces thrombus weight significantly and dose-dependently (ED 50 = 150 mg/kg/day X 3 days). Thrombocytopenia induced by injection of anti-platelet anti-serum was found not to modify thrombus formation. Yet, even in these conditions, ticlopidine remains active. Acetylsalicylic acid treatment does not prevent the antithrombotic effect of ticlopidine, indicating that its action is independent of PGI2 synthesis. These results demonstrate that ticlopidine acts as an antithrombotic agent in a venous thrombosis model in which platelets play a minor role.

Animals↗
PubMedDate not supplied

Pulsatility of 24-hour concentrations of circulating interleukin-1-alpha in healthy women: analysis of integrated basal levels, discrete pulse properties, and correlation with simultaneous interleukin-2 concentrations.

Even though it is widely known that interleukin (IL)-1 alpha acts at the local level, it is still uncertain whether IL-1 alpha is secreted into the circulation and acts at distant sites. We have tried to elucidate this by measuring 24-hour levels of total IL-1 alpha in six healthy female volunteers. Subjects had detectable and pulsatile levels of IL-1 alpha throughout the 24-hour period. The integrated 24-hour IL-1 alpha concentration was 2,367 +/- 753 min x micrograms/l (mean +/- SD), and the integrated pulsatile IL-1 alpha concentration was 553 +/- 260 (25 +/- 10% ot total integrated IL-1 alpha). The mean IL-1 alpha concentration was 1.63 +/- 0.53 micrograms/l, mean pulse frequency/24 h was 12.8 +/- 0.8, mean pulse height was 2.31 +/- 0.52 micrograms/l; mean pulse width was 80.4 +/- 2.3 min, and mean interpulse interval was 105.3 +/- 2.8 min. Total IL-1 alpha levels significantly correlated with those previously reported for IL-2 in the same samples, and IL-1 alpha pulse parameters which are concentration independent were significantly similar to those of IL-2. Furthermore, cross-correlation analysis indicated that in 83% of our subjects (5/6) there was synchronicity of IL-1 alpha and IL-2 levels. IL-1 alpha pulse parameters were in the range reported for hormones which have well-characterized pulsatility, such as growth hormone, luteinizing hormone, follicle-stimulating hormone, cortisol, beta-endorphin, and progesterone. Based on these data we speculate that a pulsatile cytokine cascade may exist in the systemic circulation.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMedDate not supplied

Low doses of endotoxin potentiate venous thrombosis in the rabbit.

Procoagulant activity of the endothelium and of monocytes was induced by an intravenous administration of a low dose of endotoxin in the rabbit. Venous thrombosis induced by a 45-min stasis of the jugular vein was dramatically increased after the administration of endotoxin. Endotoxin enhanced venous thrombosis in a dose-dependent manner which was the highest after the administration of 1 microgram/kg. This effect increased with time but was optimal when endotoxin was injected 4 h before stasis induction. Leukocytes appear to play a key role in this process since mechlorethamine-induced leukopenia totally inhibited thrombus formation. Hirudin and heparin, administered intravenously 5 min before stasis, were both potent inhibitors of endotoxin-induced venous thrombosis exhibiting ED50 values of 3.8 +/- 1.0 and 2.3 +/- 1.1 microgram/kg, respectively.

Animals↗
PubMedDate not supplied

Protamine sulphate inhibits pentasaccharide (SR80027)-induced bleeding without affecting its antithrombotic and anti-factor Xa activity in the rat.

The neutralization of a potent anti-factor Xa pentasaccharide (SR 80027) and heparin-induced bleeding enhancement by protamine sulphate was studied in vivo. Bleeding time, as measured by transection of the tail of anaesthetized rats, increased after the administration of standard heparin and SR 80027. Doses of 0.6 and 2.5 mg/kg of heparin and SR 80027, respectively, were required to enhance blood loss to the same extent (6-fold increase). Protamine sulphate (10 mg/kg i.v.) reduced blood loss induced by both compounds but also neutralized the anti-factor Xa activity as well as the antithrombotic activity of standard heparin measured in a venous thrombosis model. However, protamine sulphate did not affect the anti-factor Xa activity or the antithrombotic activity of SR 80027. These data suggest that protamine sulphate may be an effective antidote for the bleeding side-effects of SR 80027 but they also indicate that the bleeding tendency associated with this type of compounds cannot be attributed to their anti-factor Xa activity.

Animals↗
PubMedDate not supplied

[Approximation to cost analysis of various types of hemodialysis using relative value units].

Hemodialysis sessions performed in Hospital Units have a different degree of complexity depending on the kind of patients who is receiving this treatment. This paper's aim is to apply certain weighting factors, which measure the complexity of each type of session performed, and so allow a more realistic comparison with hemodialysis sessions performed in dialysis Units. The various costs of the Castellón General Hospital Dialysis Unit were calculated. Five types of Hospital-performed sessions were defined, to which were applied concrete weighting factors called Relative Value Units (RVU). These took account of health professionals' time, disposable material and drug expenses. The cost of single hemodialysis session, before the RVU calculation was added, was 28,549 pesetas (171.58 Eu.). Thirty-two per cent of the cost was from disposable material, 29.38% for cost of health professionals time, 18.54% for structural costs, 13.4% for drug expenses, and 5.73% for the nephrologists' time. When RVU were applied, the Type I session cost (chronic renal failure patients on regular hemodialysis), was 28,882 pesetas (149.54 Eu.). As the complexity of the procedure increased, up to the Type V session (acute renal failure patients in intensive Care Units), the costs also rose to 68,448 pesetas (411.38 Eu.). We conclude that weighing the different types of hemodialysis sessions by means of RVU, allows a better measurement of the costs and achieves a more accurate comparison with others hemodialysis units.

Costs and Cost Analysis↗
PubMedDate not supplied

[Granular myringitis].

We present two cases of granular myringitis. A clinical study, diagnosis and therapy of this rare condition are undertaken.

Adult↗