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Biomedical subjects

F B Taylor

Publications and source records attributed to F B Taylor.

At least 91 records · Page 5Linked to original sources
PubMed1987

Protein C prevents the coagulopathic and lethal effects of Escherichia coli infusion in the baboon.

Gram-negative septicemia elicits multiple abnormalities of the coagulation system. Although products of coagulation can lead to clot formation, thereby potentiating organ damage, recent work has shown that low concentrations of thrombin can protect animals from the shock state. Because these amounts of thrombin also lead to formation in vivo of the anticoagulant enzyme, activated protein C, we examined the role of protein C in modulation of Escherichia coli shock in baboons. First, we infused activated protein C and lethal concentrations of E. coli organisms, which prevented the coagulopathic, hepatotoxic, and lethal effects of E. coli. Second, using an antibody to protein C we blocked protein C activation in vivo to determine if this influenced the response to lethal and sublethal concentrations of E. coli organisms. Under these conditions the response to lethal concentrations of E. coli organisms was made more severe and the response to sublethal concentrations of E. coli was made lethal. The coagulopathic, hepatotoxic, and lethal responses in this latter case were prevented by infusion of exogenous protein C.

Alanine Transaminase↗
PubMed1987

Protein S is a cofactor for activated protein C neutralization of an inhibitor of plasminogen activation released from platelets.

Platelets stimulated with thrombin release an inhibitor of plasminogen activator (PAI), which has been shown previously to be neutralized by activated protein C (APC). The requirements for optimal neutralization of PAI activity were investigated. The releasate of gel-filtered human platelets stimulated with thrombin served as a source of PAI. When 6 X 10(8) platelets/mL were incubated with thrombin (1 IU/mL), the releasate contained 18 to 26 ng/mL PAI as determined by incubation of the releasate with urokinase and measurement of residual urokinase activity on plasminogen (S2251). Preincubation of PAI with up to 4 micrograms/mL APC for two hours yielded less than 20% neutralization of PAI activity. In the presence of protein S, phospholipid, and Ca2+, neutralization of PAI activity was time-dependent with 50% neutralization occurring in two hours with 1 microgram/mL APC. The cofactor effects of protein S and phospholipid were concentration-dependent with half-maximal acceleration at approximately 3 micrograms/mL protein S and 10 micrograms/mL phospholipid when the experiments were performed at 1 microgram/mL APC. Diisopropylfluorophosphate-inactivated APC, gla-domainless APC, and thrombin-cleaved protein S had no effect on PAI activity, indicating requirement for preservation of the APC active site and of the Ca2+ binding ability of both APC and protein S. These results suggest coordinate binding of APC and protein S onto phospholipid membrane as a prerequisite for optimal expression of PAI neutralized by APC.

Blood Coagulation↗
PubMed1987

Protein C, isolation and potential use in prevention of thrombosis.

Protein C and protein S serve as natural anticoagulants. Deficiencies of these proteins are often associated with recurrent deep vein thrombosis and coumarin induced skin necrosis. These two proteins function by selectively inactivating factors Va and VIIIa, two of the "cofactors" of blood coagulation. Hence, inhibition of coagulation by this pathway complements the better known inhibition mediated by the antithrombin III-heparin system. These observations suggest that protein C and/or activated protein C may prove useful in controlling thrombosis and/or DIC. We have developed a Ca2+ dependent monoclonal antibody which allows the rapid isolation of human protein C. This rapid isolation has allowed us to demonstrate that activated protein C can protect baboons from the lethal effects of E. coli/endotoxin and that protein C supplementation can minimize fibrinogen consumption following tissue factor infusion into dogs.

Animals↗
PubMed1986

Indium-111 platelet scintigraphy for the diagnosis of acute venous thrombosis.

Platelets labeled with indium-111 have been used successfully as a marker of active thrombosis in man. To establish the diagnostic accuracy of platelet scintigraphy in comparison to contrast venography in the diagnosis of acute lower limb venous thrombosis, we evaluated 103 consecutive patients divided into two groups. Platelets were labeled by the indium-111 oxine method. Patients from group I (n = 73, 56 had venograms) were asymptomatic and underwent platelet scintigraphy 1.1 +/- 0.6 days (mean +/- 1 SD) after a major orthopedic procedure. Patients from group II (n = 30, all had venograms) were symptomatic and underwent platelet scintigraphy 1.2 +/- 1.7 days after venography. In group II, 15 patients with positive findings on contrast venography were treated with intravenous heparin; five others with positive venograms did not receive heparin until platelet scintigraphy was completed. Both platelet scintigraphy and contrast venography were evaluated by two blinded observers. Only studies with blinded agreement of both platelet scintigraphy and contrast venography were included in the analysis. Sensitivity and specificity of platelet scintigraphy for the whole limb were 93% and 97% in group I and 42% and 67% in group II. The lower sensitivity in group II was most likely attributable to therapy with heparin. These results demonstrate that platelet scintigraphy, a test that permits imaging for up to five days after a single injection, correlates favorably with contrast venography in patients who have not received heparin and may be used as a surveillance test in high-risk patients. The role of platelet scintigraphy in acutely symptomatic patients requires further evaluation.

Aged↗
PubMed1985

Whole blood clot lysis: in vitro modulation by activated protein C.

Lysis of clots prepared from native or citrated whole blood as measured by release of 125I fibrinogen degradation products was 10% or less at 20 hours. Lysis of these clots was accelerated by activated protein C in a dose-dependent manner (0.1 to 20 micrograms/ml) from less than 10% to 60-80% at 20 hours. Lysis of clots prepared from native or citrated platelet poor plasma across the same concentration range of activated protein C was less than 15%. Gla-domain-less activated protein C was equally effective in accelerating clot lysis whereas DIP-activated protein C or factor Xa did not accelerate clot lysis. This suggested that this action of activated protein C was enzymatic and this this action was limited to protein C among the vitamin K dependent proteins. The unresponsiveness of platelet poor plasma to activated protein C was completely restored to that of whole blood by addition of mononuclear leukocytes. Addition of red corpuscles or platelets alone had no effect on this response, while addition of polymorphonuclear leukocytes partially restored this response. Addition of metabolic inhibitors 2-deoxyglucose and oligomycin inhibited the response of whole blood and of plasma-mononuclear leukocytes to activated protein C. Reconstitution studies of platelet poor plasma made deficient in plasminogen activator and plasminogen showed that accelerated clot lysis produced by mononuclear leukocytes and activated protein C required the presence of plasminogen. We concluded, therefore, that activated protein C accelerates whole blood or plasma-leukocyte clot lysis by modulating activation of the plasminogen system by metabolically active leukocytes.

Blood Coagulation↗
PubMed1985

A new function for activated protein C: activated protein C prevents inhibition of plasminogen activators by releasate from mononuclear leukocytes--platelet suspensions stimulated by phorbol diester.

Mononuclear leukocytes release an inhibitor of plasminogen activators. Mononuclear leukocyte mixtures (400 to 1,000/mm3) lysed fibrin (8.3 microM) clots in the presence of plasminogen (0.58 microM). Anti-urokinase IgG (0.16 microM) inhibited this fibrinolysis. 2-Deoxyglucose (5 mM) and oligomycin (2.3 microM) also inhibited fibrinolysis. Incubation of mononuclear leukocytes (3,200/microliter) with phorbol-12 myristate 13-acetate (20 nM) for ten minutes at 37 degrees C aggregated the monocyte and platelet components and inhibited fibrinolysis. The releasate from these stimulated cells in dilutions ranging from undiluted to 1:16 inhibited urokinase (1.6 pM) and tissue plasminogen activator (1.4 pM). This releasate did not inhibit plasmin (2.5 nM). Incubation of this releasate with activated protein C (33 nM to 333 nM) for ten minutes at 37 degrees C before addition of either urokinase, or tissue plasminogen activator and plasminogen completely prevented this inhibition. Thrombin, factor Xa, DIP-activated protein C had no affect on this inhibition. We conclude that activated protein C facilitates fibrinolysis by preventing inhibition of plasminogen activators. This may be a mechanism by which activated protein C increases fibrinolytic activity in vivo.

Blood Platelets↗
PubMed1984

A model for thrombin protection against endotoxin.

Infusion of dogs with thrombin (0.5 U/kg/min) for 90 minutes significantly increased percent survival following infusion of endotoxin (0.06 mg/kg/min) for 30 minutes. Nine of fourteen dogs infused with thrombin survived seven days (permanent survivors), whereas thirteen of fourteen dogs infused with saline died within 36 hours. Those dogs which survived responded immediately to endotoxin with enhanced anticoagulant and fibrinolytic activity as measured by the Xa one-stage and fibrin degradation product assays, respectively. Those dogs receiving saline instead of thrombin did not respond with anticoagulant or fibrinolytic activity until the end of the study. We concluded that thrombin in the correct amounts protected dogs from endotoxin and that this protection was associated with an early anticoagulant and fibrinolytic response to endotoxin infusion.

Animals↗
PubMed1984

Effect of crosslinking on the structure of solubilized fibrin degradation products in whole plasma.

The purpose of these studies was to establish the validity of 125I fibrin autoradiography--SDS gel techniques for monitoring degradation products from whole plasma or blood clots. These methods can be used to study fibrin degradation not only in patients with congenital factor XIII deficiency, but also in patients with disseminated intravascular coagulation or deep vein thrombosis during the course of thrombolytic therapy. Such an assay might complement existing immunologic techniques to characterize fibrin degradation in vivo by providing an in vitro analysis of the rate and pattern of fibrin degradation in whole blood or plasma. Fibrin degradation was traced by Coomassie blue staining for protein and by autoradiography on SDS-PAGE of degradation products released from a 125I-labeled fibrin tracer. The degradation of non-crosslinked clots from purified fibrin supplemented with plasmin showed a typical release of X, Y, D, and E fibrin fragments. Subsequently, all X and Y fragments were digested to D and E fragments. The degradation of non-crosslinked washed clots prepared from plasma supplemented with plasmin reflected the same pattern. The degradation of non-crosslinked washed clots prepared from EDTA anticoagulated plasma without added plasmin also showed release of X, Y, D, and E fragments. However, in contrast to the non-crosslinked washed clots supplemented with plasmin, there was no additional degradation of the X and Y fragments. These studies established that the pattern of degradation of the 125I-radiolabeled fibrin tracer was similar to that of the total protein released from the fibrin clot as observed by protein staining.(ABSTRACT TRUNCATED AT 250 WORDS)

Blood Coagulation↗
PubMed1982

Observations on optimal conditions for lysis of whole blood clots and use of this assay as a screening assay in clinical investigation.

These studies describe an assay of whole blood clot lysis as measured by release of 125I-fibrinogen degradation products. Optimal rates of lysis were obtained at 37 degrees C in 10-12 mM EDTA or 3,8% citrate and 4 u of thrombin/ml. Eighteen normal subjects and eight patients (six with recurrent deep vein thrombosis, one with thrombasthenia, and one with hepatitis and resolving portal vein thrombosis) were studied using this assay. The clots of seventeen of the eighteen normal subjects were 50% lysed at 40 hours. The clots of the patients with venous thrombosis and thrombasthenia did not lyse whereas the clots of the patient with hepatitis, resolving portal vein thrombosis and a high plasminogen activator level (0.32 CTA units) were 100% lysed at 4.5 hrs.

Blood Platelet Disorders↗
PubMed1982

Comparison of Indium-111 platelet scintigraphy and two-dimensional echocardiography in the diagnosis of left ventricular thrombi.

In a study comparing indium-111 platelet scintigraphy and two-dimensional echocardiography as methods of identifying left ventricular thrombi, the results obtained with both techniques were verified at surgery or autopsy in 53 patients--34 with left ventricular aneurysms, and 19 with mitral-valve disease. Left ventricular thrombi were found at surgery or autopsy in 14 of the patients with aneurysms and in none of those with mitral-valve disease. Thirteen of 53 echocardiograms (25 per cent) were technically inadequate and excluded from the analysis. In the group with aneurysms, the sensitivity of scintigraphy in detecting thrombi was 71 per cent, and that of echocardiography was 77 per cent. The specificity of scintigraphy was 100 per cent, and that of echocardiography was 93 per cent. We conclude that indium-111 platelet scintigraphy and two-dimensional echocardiography have useful and complementary roles in the detection of left ventricular thrombi. Both these noninvasive techniques can be used to monitor therapy.

Adult↗
PubMed1982

Effect of calcium, magnesium, and zinc on ticarcillin and tobramycin alone and in combination against Pseudomonas aeruginosa.

Correlation between in vitro and in vivo test results for synergy between carboxypenicillins and aminoglycosides against Pseudomonas aeruginosa is poor. Although the divalent cation content of culture media is known to affect aminoglycoside susceptibility testing for P. aeruginosa, this effect of divalent cations has not been examined for synergy testing of carboxypenicillin-aminoglycoside interaction against P. aeruginosa. The minimal inhibitory concentrations (MICs) of tobramycin and ticarcillin and the interaction of these drugs in combination were studied by a microtitration method for 36 strains of P. aeruginosa in Mueller-Hinton broth with varying supplements of calcium, magnesium, and zinc. The supplementation of Mueller-Hinton broth to 50 or 100 mg of calcium per liter had a significant effect in increasing the tobramycin MIC (P less than 0.01), as well as decreasing the degree of synergy between ticarcillin and tobramycin (P less than 0.01). Supplementation to 20 mg of magnesium per liter, 1.0 mg of zinc per liter, or both did not significantly affect tobramycin MIC or the interaction of tobramycin and ticarcillin. Supplementation to 50 or 100 mg of calcium per liter rendered any additional effect of magnesium and zinc on aminoglycoside MIC and aminoglycoside-carboxypenicillin interaction negligible. If these results for ticarcillin and tobramycin are confirmed for other carboxypenicillins and aminoglycosides, then the Mueller-Hinton broth used for P. aeruginosa aminoglycoside susceptibility and synergy testing may need to be supplemented only with calcium at a concentration of 50 mg/liter.

Anti-Bacterial Agents↗
PubMed1982

Plasminogen, plasminogen activator, and platelets in the regulation of clot lysis. Reconstitution and patient studies.

Dilute clot lysis was assayed by release of soluble 125I fibrin degradation products from dPPP clots containing varying amounts of plasminogen activator and platelets. Plasminogen activator in the absence of platelets gave an approximately linear rate of lysis, with a rate proportional to its concentration. Addition of platelets to achieve normal clot retraction had little effect on the lysis rate in the absence of plasminogen activator or in the presence of very high plasminogen activator levels. However, with intermediate plasminogen activator levels, platelet-mediated clot retraction was associated with an accelerated rate of clot lysis when retraction reached 75% to 90%. The length of the lag phase before the start of the accelerated phase varied with the number of platelets and rate of clot retraction. The interaction of clot retraction and lysis was further explored in selected patients to determine (1) whether the contributions of platelet and plasma factors in these cases was similar to those seen in our studies of reconstituted plasma and (2) whether our experience with reconstituted systems could be used in the study of disorders of fibrinolysis involving platelets and fibrinolytic enzymes.

Blood Coagulation↗
PubMed1981

Failure of aspirin to prevent incorporation of indium-111 labelled platelets into cardiac thrombi in man.

The in vitro and in vivo behaviour of platelets was studied in eleven patients with left ventricular aneurysms and mural thrombi. Five patients were on aspirin 300-2400 mg/day; the remaining six patients were controls. In vitro function was tested by the aggregation response of platelets to adenosine diphosphate (ADP) and collagen. In vivo function was assessed by the incorporation of indium-111-labelled platelets into cardiac thrombi as measured by scintigraphy. Platelets from patients on aspirin, whether tested before or after labelling, aggregated less with collagen than did those of controls (18 vs 52%; p less than 0.01 before labelling, 13 vs 49%; p less than 0.02 after labelling). Second wave aggregation, induced by ADP, was impaired in patients on aspirin. In all patients scintigraphy showed that the autologous labelled platelets were incorporated into ventricular thrombi. Thus, although in vitro the platelets from patients on aspirin aggregated subnormally, in vivo they took part in thrombosis.

Aspirin↗
PubMed1981

Role of pulmonary edema in the acute pulmonary response to sepsis.

There is evidence that both bronchoconstriction and accumulation of lung water may contribute to the early alterations in lung function following septicemia. Eigher of these may be mediated by blood components. To assess these proposed mechanisms the changes in hemodynamics, pulmonary mechanics, gas exchange, and gravimetric lung water were measured in the first 4 h after Escherichia coli infusion in the anesthetized dog and baboon. These species were selected because of previously demonstrated differences in the response to gram-negative sepsis. Both species developed systemic hypotension and early hypoxemia. The dogs had early transient increases in venous admixture (Qva/Qt) but not shunt or dead space, while the baboon had a more persistent increase in Qva/Qt and a late increase in dead space, Increases in nonelastic resistance and decreases in lung compliance were preceded or accompanied by decreases in the leukocyte count in both species, but the platelet count, fibrinogen, and total hemolytic complement had different changes in the two species. Postmortem lung analysis revealed increased lung weight in both species but the wet weight-to-dry weight ratio was not increased in either species. The fractional water content of the excess lung mass was less than that of whole blood. Histological examination revealed large numbers of extravasated leukocytes in the lungs, which may be sufficient to explain the increase in lung weight. We conclude that pulmonary edema does not play a role in the early pulmonary response to E. coli bacteremia in either species. The physiological changes observed are more consistent with bronchoconstriction.

Animals↗