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Biomedical subjects

J Hirsh

Publications and source records attributed to J Hirsh.

At least 307 records · Page 17Linked to original sources
PubMed1988

Antithrombotic properties of heparin in a neonatal piglet model of thrombin-induced thrombosis.

The relative deficiency of antithrombin III (AT III) in neonatal plasma results in lower recovery of heparin in some assay systems. It is uncertain whether low AT III levels also limit the antithrombotic effects of heparin in this age group. We therefore compared the antithrombotic properties of heparin in mature pigs and newborn piglets, whose coagulation and inhibitor system closely resembles that of the human neonate. Animals were pretreated with saline, 10 or 25 U/kg heparin (n greater than or equal to 16 per age group and dose). Following an injection of 100 U/kg thrombin, systemic 125I-fibrinogen consumption and local 125I-fibrinogen incorporation into jugular venous stasis thrombi were measured. Significantly more 125I-fibrinogen was consumed in piglets than in pigs systemically (p less than 0.0001), as well as within the occluded vein segment (p = 0.0112), largely because heparin was less effective in piglets than in pigs. This neonatal resistance to heparin could not be explained by lower heparin levels in the newborn animals. However, pretreatment with AT III concentrate significantly improved the antithrombotic properties of heparin in this age group (p less than 0.0001). We conclude that physiologically low AT III levels reduce the efficacy of heparin in neutralizing thrombin activity in newborn piglets. We speculate that AT III deficiency may also limit the antithrombotic properties of heparin in newborn infants with thrombotic disease.

Animals↗
PubMed1988

Randomised comparison of two intensities of oral anticoagulant therapy after tissue heart valve replacement.

After tissue heart valve replacement 108 patients were randomised to standard anticoagulant control with rabbit brain thromboplastin (Dade C reagent, therapeutic range 18-24 s; international normalised ratio 2.5-40) and 102 to a less intensive regimen controlled with human brain thromboplastin (Manchester Comparative Reagent, therapeutic range 26-30 s; INR 2.0-2.25). Treatment was continued for three months, outcome measures being major or minor embolism or haemorrhage. 2 patients in each group had major embolic events and 11 in each group had minor embolic events. The 95% confidence intervals on the differences are -3.4% to 3.2% for major embolism and -9.3% to 8.2% for minor embolism. Haemorrhagic complications were significantly more frequent with standard treatment (15 patients) than with the less intensive regimen (6 patients); and of the 5 patients with major haemorrhagic complications, all were in the standard treatment group, again a significant difference. The less intensive regimen is thus no less effective and safer than standard anticoagulant therapy in patients with tissue heart valve replacement.

Administration, Oral↗
PubMed1988

The thrombogenic effect of anticancer drug therapy in women with stage II breast cancer.

Thromboembolic disease has long been recognized as a complication of cancer. Recent reports have suggested that drugs used in the treatment of cancer, including chemotherapeutic agents and hormones, may contribute to this risk, but it has not been possible to separate the effect of these drugs from that of the cancer. We performed a randomized trial comparing 12 weeks of chemohormonal therapy (using cyclophosphamide, methotrexate, fluorouracil, vincristine, prednisone, doxorubicin, and tamoxifen) with 36 weeks of chemotherapy (using cyclophosphamide, methotrexate, fluorouracil, vincristine, and prednisone) in patients with Stage II breast cancer. Among 205 patients randomly assigned to treatment, there were 14 episodes of thrombosis (6.8 percent). These 14 episodes occurred during 979 patient-months of chemotherapy; by comparison, there were no events during 2413 patient-months without therapy. During the first 12 weeks of the study, five patients in the 12-week group and four patients in the 36-week group had thrombosis. During the subsequent 24 weeks, when only patients in the 36-week group were still receiving chemotherapy, there was no thrombosis in the 12-week group, but there were five additional events in the 36-week group (P = 0.03). These findings suggest that chemotherapy contributes to thrombosis in patients with breast cancer.

Antineoplastic Combined Chemotherapy Protocols↗
PubMed1988

A cis-acting element and associated binding factor required for CNS expression of the Drosophila melanogaster dopa decarboxylase gene.

A cis-acting sequence from the Drosophila melanogaster dopa decarboxylase (Ddc) gene is selectively required for Ddc expression in the central nervous system. We analyze several parameters influencing the function of the sequence element and describe a factor which interacts with it and mediates CNS expression of Ddc. The element, element I, can function in vivo when included on a synthetic oligonucleotide inserted near its normal location, or closer to the RNA startpoint. It displays partial activity when inverted. Two different 2-bp mutations in element I abolish its ability to stimulate neuronal Ddc expression in the CNS. A factor present in embryonic nuclear extracts specifically protects element I in DNase I footprinting assays. The binding affinity of this factor is reduced by each alteration of element I that inhibits neuronal expression, indicating a role in mediating CNS expression of Ddc. Element I alone has no detectable activity when placed adjacent to a heterologous promoter, although 2.2 kb of 5' Ddc sequences direct correct cell-specific expression of a heterologous promoter.

Animals↗
PubMed1988

Sialic acid and neuraminidase activity in rat kidneys 6 months after uninephrectomy.

Sialic acid and neuraminidase activity were determined in the cortex of the remnant kidneys of six uninephrectomized rats. As controls served either the kidneys removed at operation or age-matched kidneys from eight sham operated rats. Six months after uninephrectomy the kidneys became hypertrophied and their mean weight was about 40% higher than age-matched kidneys. Blood urea and creatinine and protein levels in 24-hr urine collections were significantly higher in the experimental animals as compared to those of the same animals before nephrectomy and to sham operated rats, indicating a marked impairment of kidney function. The mean concentration of sialic acid in the cortex of hypertrophied kidneys was not statistically different from either that of the removed or that of the age-matched kidneys. Neuraminidase activity expressed as either per gram fresh tissue or per milligram protein, was not different in the removed and in the hypertrophied kidney. The activity, however, in the latter was significantly lower than in the age-matched kidneys. Whether this finding can be associated with the impairment of kidney function in rats 6 months after uninephrectomy remains to be studied.

Animals↗
PubMed1988

Optimum use of anticoagulants in pregnancy.

Pregnant women pose special problems when deciding upon optimal anticoagulant therapy. Heparin does not cross the placenta and is probably safe for the fetus. Long term heparin therapy is occasionally associated with maternal haemorrhage and rarely with symptomatic osteoporosis. Coumarin derivatives, however, cross the placenta and are potentially teratogenic, particularly in the first trimester. Neonatal infant haemorrhage is a possibility if warfarin is administered to the pregnant mother near term. For the prevention and treatment of venous thromboembolism, heparin is the anticoagulant of choice since its safety and efficacy are well established. For the prevention of systemic embolism associated with prosthetic heart valves or valvular heart disease, the efficacy of heparin has not been established. Nevertheless, 12-hourly subcutaneous heparin in doses to prolong a mid-interval activated partial thromboplastin time (aPTT) to 1.5 times control is likely to be effective and safe. An alternative is to use heparin for the first trimester, change to warfarin until the middle of the third trimester, then to restart heparin until term. However, before warfarin is used in pregnant patients, the risks should be carefully explained to the patient to help avoid medicolegal problems. Warfarin can be safely used postpartum by the breast-feeding mother.

Adult↗
PubMed1988

An overview of clinical trials of low molecular weight heparin fractions.

There is experimental evidence that low molecular weight heparin fractions are as effective as standard unfractionated heparin but cause less bleeding. In order to determine the efficacy and safety of low molecular weight heparins, we have conducted an overview of published randomized trials in which a low molecular weight heparin was compared to either placebo or to unfractionated heparin. In the two trials comparing low molecular weight heparin prophylaxis with placebo, the incidence of leg vein thrombosis was substantially reduced with low molecular weight heparin and there was no increased bleeding risk. There have been five trials which compared low molecular weight heparin with unfractionated heparin in high risk surgical patients. In one of these studies there was a statistically significant reduction in postoperative venous thrombosis in patients who received the low molecular weight heparin. In the remaining studies, thrombosis rates were relatively low in all groups and no difference was detected between low molecular weight heparin and unfractionated heparin. We found a significant relationship between ex vivo anti-factor Xa levels and clinically important bleeding, r = 0.54. We conclude that low molecular weight heparin is an effective method of prophylaxis and has a negligible risk of bleeding provided that the anti-factor Xa levels do not exceed 0.2 units per ml. There have been only three published randomized trials on the efficacy of low molecular weight heparin in the treatment of venous thrombosis. Much larger studies are required to establish the efficacy and safety of low molecular weight heparin fractions in the treatment of established venous thromboembolism.

Clinical Trials as Topic↗
PubMed1988

The treatment of venous thromboembolism.

Venous thromboembolism is usually treated with heparin followed by oral anticoagulants for approximately 3 months. The optimal length of heparin therapy is uncertain. There is now good evidence that treatment failures are associated with inadequate heparin effects. Heparin can be administered with similar safety and effectiveness by either intravenous infusion or 2 hourly subcutaneous injection. Oral anticoagulant therapy is effective and safe if given in a dose which prolongs the prothrombin time to an international normalized ratio of 2.0 to 2.5. Thrombolytic therapy is indicated in patients with major pulmonary embolism and in selected patients with recent acute venous thrombosis. Vena caval interruption is usually confined to patients who have contraindications to anticoagulant therapy. Surgical removal of thromboembolic obstruction should be considered in selected patients with thromboembolic pulmonary hypertension.

Anticoagulants↗
PubMed1988

Pulmonary embolism in outpatients with pleuritic chest pain.

Pleuritic chest pain is a frequent complaint in patients coming to the emergency room, but the proportion of such patients with pulmonary embolism is uncertain. In a prospective study, we evaluated the diagnostic outcomes in 173 consecutive patients who came to the emergency room with pleuritic chest pain. Pulmonary embolism, as demonstrated by angiography or autopsy, was present in 36 (21%). The need for objective testing is clearly indicated by our finding that the sensitivity (85%) and specificity (37%) of predetermined clinical variables for pulmonary embolism were insufficient to allow a definitive treatment decision. Optimal sensitivity and specificity are obtained by using pulmonary angiography in combination with lung scanning. The proportion of patients requiring angiography is substantially reduced, from 43% to 26%, without significant loss of accuracy, if ventilation imaging and impedance plethysmography are used together with perfusion scanning.

Adult↗
PubMed1987

Sample size in the planning and interpretation of clinical trials.

An understanding of sample size determination is important in both planning and interpreting the results of clinical trials. A Type II error occurs when it is concluded that there is no difference between treatment groups, when in truth there is a difference. Such a false negative conclusion results from too few patients in a trial. In this review the principles of estimating sample size before a trial is commenced and evaluating the results of a negative completed trial are reviewed. Clinically relevant examples are used to illustrate these concepts.

Biometry↗
PubMed1987

The basement membrane underlying the vascular endothelium is not thrombogenic: in vivo and in vitro studies with rabbit and human tissue.

Studies examining the interaction of platelets with exposed subendothelium in vivo have reported conflicting results. To examine possible explanations for the apparently discrepant findings, we measured the platelet reactivity of subendothelium prepared by a number of methods both in vivo and in vitro. In addition, we examined the possibility that 13-hydroxyoctadecadinoic acid (13-HODE), an endothelial cell-derived chemorepellant, modulates the reactivity of the subendothelium to platelets. In vivo, the subendothelium of segments of rabbit carotid arteries was exposed by removing the endothelial cells by air perfusion or by balloon catheter stripping. Platelet accumulation onto the de-endothelialized segments was assessed by 3H-radioactivity uptake, using 3H-adenine-labelled platelets, and by scanning electron microscopy. In vitro, 3H-adenine-labelled platelet adhesion was measured onto plain plastic discs and onto plastic discs coated with the following purified basement membrane components: collagens type I, III, IV, V, laminin, or fibronectin. In addition, 3H-adenine-labelled platelet adhesion was measured onto plastic discs covered with human endothelial cells or onto the basement membrane underlying the endothelial cells. In vivo, there was marked 3H-platelet accumulation onto the balloon catheter carotid arteries one hour after injury. In contrast, there was no platelet accumulation onto the subendothelium of carotid arteries de-endothelialized by air perfusion. These differences were confirmed by scanning electron microscopy. Transmission electron microscopic examination demonstrated that the extracellular matrix was intact following the air perfusion injury whereas the majority of it was removed by the balloon catheter injury.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1987

Evidence for a saturable mechanism of disappearance of standard heparin in rabbits.

This work demonstrates that after bolus intravenous injection standard heparin (SH) disappearance results from the combination of a saturable and a non saturable mechanism. Pharmacokinetics and pharmacodynamics of SH were studied by measuring the disappearance of increasing doses (5 - 500 anti-factor Xa U/kg) of 125I-heparin and of its biological effects. CPM curves allowed to determine the half lives of heparin according to the dose injected. The half lives were clearly dose dependent and reached a plateau over 100 anti-factor Xa U/kg. The complex curve which describes the amount of heparin cleared per time unit after any given dose has been resolved into its two components reflecting a saturable and a non saturable mechanism of disappearance. For the doses less than 100 anti-factor Xa U/kg the saturable mechanism was preeminent and the anti-factor Xa activity disappearance followed an exponential pattern; for the doses less than 100 anti-factor Xa U/kg the contribution of the non saturable mechanism becomes more important and the anti-factor Xa activity disappearance followed a concave-convex pattern. Further experiments showed that the heparin half life shortened as the circulating anti-factor Xa activity decreased; this phenomenon may explain the concave-convex pattern of the curve of the anticoagulant effect observed after injection of large doses of SH.

Animals↗