Search PubMed⌕ Search

Biomedical subjects

J Hirsh

Publications and source records attributed to J Hirsh.

At least 325 records · Page 18Linked to original sources
PubMed1987

The disappearance of a low molecular weight heparin fraction (CY 216) differs from standard heparin in rabbits.

In previous studies, we have reported that standard heparin (SH) was cleared by two mechanisms, a saturable mechanism which predominated at low doses (less than 100 anti-factor Xa U/kg) and a non-saturable mechanism which predominated at higher doses, when the first mechanism became saturated. In this study, we examined the importance of these two mechanisms in the disappearance of a low molecular weight heparin fraction (LMWH) (CY 216), by comparing the pharmacokinetics and the pharmacodynamics of a wide range of doses of SH and CY 216 (1.5 to 500 anti-factor Xa U/kg). Pharmacokinetics was measured as the disappearance of 125I-radiolabelled SH or CY 216. Pharmacodynamics was measured as the disappearance of the anti-factor Xa activity of SH and CY 216. We found that the saturable mechanism contributed little to the disappearance of CY 216 and that it was cleared predominantly by the non-saturable mechanism at all doses tested. Thus, at low doses (less than 100 anti-factor Xa U/kg), SH was cleared more rapidly than CY 216, whereas at higher doses, CY 216 was cleared more rapidly than SH. We conclude that the mechanism of disappearance of LMWH's differ significantly from those of SH, and that this difference may explain the apparent prolonged anticoagulant activity of LMWH's within the therapeutic range doses.

Animals↗
PubMed1987

Catalysis of thrombin inhibition provides an index for estimating the antithrombotic potential of glycosaminoglycans in rabbits.

Previous studies have demonstrated that standard anticoagulant tests are poor indices of the antithrombotic potential of glycosaminoglycans which are weak catalysts of the thrombin-antithrombin III reaction. In this study we investigated whether the catalysis of thrombin inhibition by plasma could serve as a reliable index for assessing the antithrombotic effectiveness of glycosaminoglycans. Equal volumes of 125I-thrombin and control or test plasma were incubated for up to 10 min at 37 degrees C. Inactivation of thrombin was then determined after 7.9% SDS-polyacrylamide gel electrophoresis and subsequent autoradiography. Increasing concentrations of heparin (greater than 0.066 micrograms/mL or 0.01 USP units/mL) and dermatan sulfate (greater than 0.1 micrograms/mL) could be readily demonstrated in undiluted plasma by enhanced formation of complexes of thrombin with antithrombin III and heparin cofactor II respectively. However, the detection of any catalytic effect of the two glycosaminoglycans decreased significantly with increasing plasma dilutions. When ex vivo plasmas obtained from rabbits that had been injected with the minimum dose of any one of seven glycosaminoglycans required to achieve their optimal antithrombotic effect were assessed for their ability to catalyse thrombin inhibition, there was approximately a 2-fold increase in the amount of thrombin inactivated 30 s after the thrombin had been added to the plasma. The enhanced inhibition of thrombin was achieved by catalysis of antithrombin III and/or heparin cofactor II activities. These results suggest that measurement of the catalysis of thrombin inactivation in undiluted plasma is a sensitive and reliable index for estimating the antithrombotic potential of glycosaminoglycans in rabbits.

Animals↗
PubMed1987

The inhibition of thrombin-dependent positive-feedback reactions is critical to the expression of the anticoagulant effect of heparin.

Heparin catalyses the inhibition of two key enzymes of blood coagulation, namely Factor Xa and thrombin, by enhancing the antiproteinase activities of plasma antithrombin III and heparin cofactor II. In addition, heparin can directly inhibit the activation of Factor X and prothrombin. The contributions of each of these effects to the anticoagulant activity of heparin have not been delineated. We therefore performed experiments to assess how each of these effects of heparin contributes to its anticoagulant activity by comparing the effects of heparin, pentosan polysulphate and D-Phe-Pro-Arg-CH2Cl on the intrinsic pathway of coagulation. Unlike heparin, pentosan polysulphate catalyses only the inhibition of thrombin by plasma. D-Phe-Pro-Arg-CH2Cl is rapid enough an inhibitor of thrombin so that when added to plasma no complexes of thrombin with its inhibitors are formed, whether or not the plasma also contains heparin. Heparin (0.66 microgram/ml) and pentosan polysulphate (6.6 micrograms/ml) completely inhibited the intrinsic-pathway activation of 125I-prothrombin to 125I-prothrombin fragment 1 + 2 and 125I-thrombin. On the addition of thrombin, a good Factor V activator, to the plasma before each sulphated polysaccharide, the inhibition of prothrombin activation was demonstrable only in the presence of higher concentrations of the sulphated polysaccharide. D-Phe-Pro-Arg-CH2Cl also completely inhibited the intrinsic-pathway activation of prothrombin in normal plasma. The inhibitory effect of D-Phe-Pro-Arg-CH2Cl was reversed if thrombin was added to the plasma before D-Phe-Pro-Arg-CH2Cl. The inhibition of the activation of prothrombin by the three agents was also abolished with longer times with re-added Ca2+. Reversal of the inhibitory effects of heparin and pentosan polysulphate was associated with the accelerated formation of 125I-thrombin-antithrombin III and 125I-thrombin-heparin cofactor complexes respectively. These results suggest that the anticoagulant effects of heparin and pentosan polysulphate are mediated primarily by their ability to inhibit the thrombin-dependent activation of Factor V, thereby inhibiting the formation of prothrombinase complex, the physiological activator of prothrombin.

Calcium↗
PubMed1987

Double-blind randomised trial of Org 10172 low-molecular-weight heparinoid in prevention of deep-vein thrombosis in thrombotic stroke.

In a double-blind, randomised trial Org 10172 low-molecular-weight (LMW) heparinoid was compared with placebo in the prevention of deep-vein thrombosis in patients with acute thrombotic stroke. Prophylaxis was started within 7 days of the onset of stroke with a loading dose of 1000 anti-factor-Xa units intravenously followed by a fixed dose of 750 anti-factor-Xa units twice a day subcutaneously; it was continued for 14 days or until hospital discharge, if earlier. 50 patients were randomised to receive Org 10172 and 25 to receive placebo. All patients underwent surveillance with I125-fibrinogen leg scanning and impedance plethysmography. Venography was carried out if either test became positive. Venous thrombosis occurred in 2 of 50 patients (4.0%) given Org 10172 and 7 of 25 patients (28.0%) given placebo (p = 0.005); the corresponding rates of proximal-vein thrombosis were 0% and 16%, respectively (p = 0.01). There was one major haemorrhage in the Org 10172 group and one minor bleed in the placebo group.

Acute Disease↗
PubMed1987

Optimal dosage regimens of tissue-type plasminogen activator.

The optimal therapeutic regimen for t-PA in humans remains to be determined. The ideal dosage regimen for t-PA should achieve effective thrombolysis as quickly as possible with minimum fibrinogenolysis to minimize bleeding. Our findings in rabbits suggest that the present regimens in humans might be improved by using frequent rapid infusions rather than the more prolonged infusions. Clearly, the results of our animal studies will have to be confirmed in man before firm recommendations can be made.

Animals↗
PubMed1987

A novel whole blood capillary technic for measuring the prothrombin time.

The prothrombin time (PT) is frequently performed to monitor anticoagulant therapy. Although relatively simple to perform, it requires venipuncture and laboratory resources for sample handling and analysis. A recently developed capillary whole blood device that uses fingerstick samples was evaluated. Paired capillary whole blood and reference plasma PTs were performed in 858 samples from 732 subjects. The PT for normal volunteers (n = 193) was 11.8 +/- 0.9 seconds with the use of the new instrument and 12.1 +/- 0.5 seconds with the use of the reference method. In samples from 539 patients receiving anticoagulants, the correlation coefficient between the two methods was 0.96. Venous whole blood without anticoagulant and capillary whole blood gave equivalent results, which suggests that the fingersticks do not effect the quality of the specimen. Variation in hematocrit between 23.4% (0.34) and 53.8% (0.538) did not alter the performance of the instrument. The new instrument is easy to use and may allow testing by nonlaboratory personnel and patients. It obviates the need for venipuncture, provides immediate results, and appears to be comparable in accuracy to current reference methods.

Anticoagulants↗
PubMed1987

Regulation of the Drosophila dopa decarboxylase gene in neuronal and glial cells.

A cis-regulatory element selectively required for the Drosophila melanogaster dopa decarboxylase gene (Ddc) in the central nervous system has been identified previously (Scholnick et al. 1986). Here, we show that at least one additional regulatory element is required for normal neuronal expression of Ddc. We find that Ddc is normally expressed in about 125 discrete neurons and in a diffused network comprising a subset of glial cells. The expression of in vitro-altered Ddc genes was studied by immunohistochemistry following germ line reintegration with P-element vectors. Normal neuron-specific Ddc gene expression requires both the initially identified element (element I) which is 60 bp upstream from the RNA start site, and an additional regulatory element located 800-2200 bp upstream. This latter element is required for neuronal expression but is not necessary for glial expression of Ddc. We provide a model to explain how interactions between multiple regulatory elements may serve to specify cell-specific gene expression.

Animals↗
PubMed1987

Treatment of pulmonary embolism.

Most clinically important pulmonary emboli are associated with thrombosis of the proximal deep veins of the leg. Anticoagulant therapy is highly successful in reducing death and recurrence from pulmonary embolism and is the treatment of choice in the majority of these patients. Thrombolytic therapy is usually reserved for selected patients with clinically serious or massive pulmonary embolism. Vena caval interruption is limited to patients who have an absolute contraindication to anticoagulant therapy or who develop recurrent pulmonary embolism despite adequate anticoagulant therapy. Pulmonary embolectomy has a high mortality and should therefore be restricted to the most desperate cases.

Heparin↗
PubMed1987

Adjusted subcutaneous heparin or continuous intravenous heparin in patients with acute deep vein thrombosis. A randomized trial.

STUDY OBJECTIVE: To determine the efficacy and safety of adjusted subcutaneous calcium heparin compared with continuous intravenous calcium heparin as the initial treatment for acute deep vein thrombosis. DESIGN: Randomized control trial. SETTING: University-affiliated general hospital. PATIENTS: Of 111 consecutive patients considered, 103 had acute proximal or calf vein thrombosis confirmed by ascending venography and met all other eligibility criteria. INTERVENTIONS: PATIENTS were randomly assigned to receive subcutaneous or intravenous heparin. The subcutaneous regimen consisted of an initial dose of 15,000 U, adjusted thereafter to prolong the activated partial thromboplastin time to 50 to 70 seconds. The continuous intravenous regimen was begun as a bolus injection of 5000 U, followed by an infusion of 1250 U/h, adjusted to maintain the activated partial thromboplastin time at 50 to 70 seconds. MEASUREMENTS AND MAIN RESULTS: There was no significant difference in the rate of new pulmonary embolism between the two groups, as defined by new high-probability defect on repeat ventilation-perfusion scintigrams of the lung in 96 (93%) of the patients after 7 to 10 days of treatment. Five of forty-seven patients in the subcutaneous group and 5 of 49 in the intravenous group developed pulmonary embolism (95% confidence interval [CI] for the difference, -13.1% to 12.2%). Similarly, there was no significant difference in the frequency of hemorrhagic complications. Five of fifty-one patients in the subcutaneous group and 5 of 52 in the intravenous group had hemorrhagic complications (95% CI for the difference, -11.2% to 11.6%). CONCLUSION: Adjusted subcutaneous calcium heparin may be an effective and safe alternative to continuous intravenous calcium heparin in the initial treatment of acute proximal deep vein thrombosis.

Acute Disease↗
PubMed1986

Regulated splicing produces different forms of dopa decarboxylase in the central nervous system and hypoderm of Drosophila melanogaster.

The dopa decarboxylase gene (Ddc) of Drosophila melanogaster is expressed in the hypoderm and the nervous system and promoter elements mediating differential expression in these tissues have been identified (Scholnick et al., 1986). Here we report an additional mode of regulation; the unique primary transcript of the Ddc gene is spliced to form mRNAs in these two tissues which differ by a single internal exon. In vitro mutagenesis and P-element-mediated transformation were employed to manipulate the tissue-specific expression of these RNAs. This approach demonstrated that regulated splicing rather than differential stability causes the tissue-specific expression of these RNAs and allowed the identification of Ddc enzyme isoforms encoded by each mRNA. The Ddc enzyme in the central nervous system differs from the hypodermal Ddc protein by the addition of 33-35 amino acids on the N terminus.

Animals↗
PubMed1986

CNS and hypoderm regulatory elements of the Drosophila melanogaster dopa decarboxylase gene.

Expression of the dopa decarboxylase gene (Ddc) is regulated in a tissue- and developmental stage-specific manner throughout the life cycle of the fruit fly, Drosophila melanogaster. Essential Ddc regulatory elements lie within 208 base pairs upstream from the RNA start point. Functional elements within this 5' flanking region were mapped by deletion analysis, which assayed expression in vivo after germline integration via P element vectors. One of the elements is essential for expression in both the larval and adult central nervous system, and at least two other elements are necessary for quantitatively normal expression in the hypoderm. Within each of the intervals that have regulatory effects are found sequence elements conserved between the Ddc genes of two distantly related species of flies. On the basis of this correlation, regulatory functions for these sequence elements can be postulated.

Animals↗
PubMed1986

Continuous intravenous heparin compared with intermittent subcutaneous heparin in the initial treatment of proximal-vein thrombosis.

We performed a randomized double-blind trial comparing continuous intravenous heparin with intermittent subcutaneous heparin in the initial treatment of 115 patients with acute proximal deep-vein thrombosis. Intermittent subcutaneous heparin as administered in this trial was inferior to continuous intravenous heparin in preventing recurrent venous thromboembolism. The subcutaneous heparin regimen induced an initial anticoagulant response below the target therapeutic range in the majority of patients and resulted in a high frequency of recurrent venous thromboembolism (11 of 57 patients, 19.3 percent), which was virtually confined to patients with a subtherapeutic anticoagulant response. In contrast, continuous intravenous heparin induced a therapeutic anticoagulant response in the majority of patients and a low frequency of recurrent events (3 of 58 patients, 5.2 percent; P = 0.024); the recurrences were limited to patients with an initial subtherapeutic anticoagulant response. The results of this trial establish the efficacy of intravenous heparin in the treatment of proximal venous thrombosis and suggest a relation between the effectiveness of heparin and the levels of anticoagulation achieved; such a relation could explain the observed failure of the subcutaneous regimen.

Acute Disease↗
PubMed1986

A randomized controlled trial of a low-molecular-weight heparin (enoxaparin) to prevent deep-vein thrombosis in patients undergoing elective hip surgery.

There is experimental evidence that low-molecular-weight fractions of heparin are as effective as the standard form but cause less bleeding. We therefore performed a double-blind, randomized trial comparing PK10169 low-molecular-weight heparin with placebo for the prevention of venous thrombosis in patients undergoing elective hip surgery. Prophylactic treatment with a fixed dose was begun postoperatively and continued for 14 days. Fifty patients in each treatment group underwent surveillance with [125I]fibrinogen leg scanning and impedance plethysmography. In the first 24 patients, venography was performed only if either surveillance test was positive. Because the rate of venous thrombosis detected in those patients was unexpectedly low, venography was requested in the remaining 76 patients, even if the screening tests were negative. In this latter group, venous thrombosis occurred in 4 patients (10.8 percent) given PK10169 heparin and 20 patients (51.3 percent) given placebo (P = 0.0002); the corresponding rates for proximal-vein thrombosis were 5.4 percent and 23.1 percent, respectively (P = 0.029). In the entire group of 100 patients, venous thrombosis occurred in 12 percent of those given PK10169 heparin and 42 percent of those given placebo (P = 0.0007), and the corresponding rates for proximalvein thrombi were 4 percent and 20 percent, respectively (P = 0.014). The observed hemorrhagic rate was 4 percent in each treatment group. We conclude that prophylaxis with fixed-dose PK10169 heparin is effective and safe for patients undergoing elective hip replacement.

Aged↗