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Biomedical subjects

E Gray

Publications and source records attributed to E Gray.

At least 73 records · Page 4Linked to original sources
PubMed1993

Antithrombotic activity and its relationship to in vitro anticoagulant effects.

Antithrombotic activities of low molecular weight heparins (LMWHs) in a venous stasis thrombosis model, when compared to unfractionated heparin (UFH), correlated better with anti-IIa activities and inhibition of thrombin generation than with anti-Xa activities. The relative antithrombotic potencies of LMWHs were closer to inhibitory activity in thrombin generation with platelet-poor plasma than platelet-rich plasma. Comparing activities in intrinsic and extrinsic systems, higher concentrations of heparins were required in vitro to inhibit intrinsic thrombin generation than extrinsic thrombin production; however, higher doses were required to prevent in vivo thrombotic events initiated via the extrinsic pathway.

Animals↗
PubMed1992

Anti-hepatitis C virus (HCV) screening at a Canadian Red Cross center: significance of a positive c100 HCV enzyme-linked immunosorbent assay.

The c100 hepatitis C virus (HCV) enzyme-linked immunosorbent assay (ELISA) has been used to screen blood donors to prevent transfusion-associated non-A,non-B hepatitis. This test is not specific, and only about 25 percent of c100 HCV ELISA-positive blood samples appear to transmit hepatitis C. However, the intensity of the ELISA (sample/cutoff ratio [S/C], greater than 2) could identify a subpopulation of donors that are at high risk for transmitting hepatitis. Blood samples from 20,186 volunteer blood donors at a Canadian Red Cross blood transfusion center were screened for antibodies to HCV using the c100 HCV ELISA. Fifty-nine (0.3%) of these donors were repeatably reactive on ELISA. When their samples were tested with the c100 recombinant immunoblot assay (RIBA) and second-generation RIBA (RIBA-2), 26 (44%) and 31 (52%) samples, respectively, were found to be positive. Thirty-three of the 59 ELISA-reactive donors had an S/C greater than 2. Of these 33 donors, 30 (91%) had elevated alanine aminotransferase (ALT), 27 (82%) were RIBA-2 positive, and 22 (67%) had risk factors for hepatitis. In contrast, of the 26 ELISA-reactive donors with S/C less than 2, only 7 (27%) had elevated ALT, and 4 (15%) were RIBA-2 positive and also had high risk factors for hepatitis. Thus, while the HCV ELISA may lack specificity, its intensity can serve to identify a subgroup of donors that are at high risk for transmitting hepatitis.

Adult↗
PubMed1992

Inhibition of thrombin generation by heparin and low molecular weight (LMW) heparins in the absence and presence of platelet factor 4 (PF4).

The ability of several low molecular weight (LMW) heparins and unfractionated heparin (UFH) to inhibit thrombin generation, and their anti-Xa and anti-IIa activities, were measured in the absence and presence of platelet factor 4 (PF4). The LMW heparins studied were 2-5 times less potent, on a weight basis, than UFH as inhibitors of thrombin generation in platelet-poor plasma; the inhibition of thrombin generation by LMW heparins correlated better with their anti-IIa activity (r = 0.98) than with their anti-Xa activity (r = 0.69). At low concentrations of PF4, the activity of LMW heparins in the thrombin generation test was neutralized less than that of UFH, but at higher PF4 concentrations all their activities could be neutralized except in anti-Xa assays. These observations support the hypothesis that anti-IIa activity is important for inhibition of thrombin generation by LMW heparins in vitro. However, when all the anti-IIa activity of LMW heparins was neutralized by PF4, considerable inhibitory activity remained in thrombin generation and anti-Xa assays, indicating that a portion of the anti-Xa activity of LMW heparins also contributes towards inhibition of thrombin generation.

Factor Xa Inhibitors↗
PubMed1992

Acute joint inflammation alters the adrenoceptor profile of synovial blood vessels in the knee joints of rabbits.

Experiments were carried out to examine the effect of acute inflammation, induced by intra-articular injection of 2% carrageenan, on the response of articular blood vessels in the knee joints of rabbits to adrenoceptor agonists. The responses to noradrenaline, phenylephrine, clonidine, UK-14304, and isoprenaline were examined 24 hours after carrageenan injection and compared with those of normal animals. Antagonists specific for alpha 1 and alpha 2 were used to identify the adrenoceptors through which the responses were mediated and to examine if carrageenan treatment altered the adrenoceptor profile of these blood vessels. The evidence suggests that in the carrageenan treated animals there is a reduction in the alpha 1 response with an associated increase in the alpha 2 response. A decrease in the number or affinity of alpha 1 adrenoceptors is indicated by the shift to the right of the noradrenaline and phenylephrine dose/response curves, whereas an increase in alpha 2 affinity or number is suggested by the associated leftward shift in the alpha 2 adrenoceptor agonist curves. This change in receptor profile appears to arise as a direct result of carrageenan induced joint inflammation.

Acute Disease↗
PubMed1991

The effect of interleukin-1 on venous endothelium--an ultrastructural study.

The effect of systemic interleukin-1 (IL-1) on venous endothelium in the presence and absence of stasis has been studied by scanning electron microscopy (SEM). Recombinant human IL-1 beta at a concentration of 1 micrograms/kg or saline was injected intravenously into rabbits and allowed to circulate for 0.5 or 4.0 h after which complete stasis was induced for 1 h in an isolated segment of each jugular vein. One vein segment was then excised and the contents examined macroscopically for thrombi, while the other segment was fixed for SEM examination. When examined by SEM the endothelium from rabbits injected with IL-1 beta was perturbed with increased surface microvilli, blebs and gaps at cell junctions when compared with saline controls. Fibrin deposition was also observed after IL-1 beta, as was the adherence of essentially non-activated platelets to intact endothelium. However, macroscopic thrombi were not formed in isolated vein segments. We conclude that although fibrin strands and platelets were deposited on the endothelium, IL-1 is not a sufficiently powerful procoagulant stimulus to lead to an occlusive thrombus in acute experiments.

Animals↗
PubMed1991

Anti-Xa clotting activities in different hepatic-triglyceride lipase preparations from post-heparin plasma.

Two different preparations of hepatic triglyceride lipase (HTGL) with comparable lipolytic activities, purified from post-heparin human plasma, were assessed for their anti-Xa activities by two clotting and one chromogenic method. Preparation 1, prepared by heparin affinity followed by ion exchange chromatography, did not contain antithrombin III and exhibited no anti-Xa activity in any of the assay systems. Preparation 2, prepared by two consecutive heparin affinity chromatography steps, was active in all three assay systems, and was shown to contain antithrombin III (AT III). Addition of purified AT III to preparation 1 did not result in the anti-factor Xa activity of preparation 2, and monoclonal antibodies to AT III did not antagonize the activity of preparation 2. These results show that the anti-Xa activity of some HTGL preparations is neither due to the lipase itself nor to the content of AT III, but suggest, that it could be due to contamination with another protein, which binds to heparin sepharose columns but is removed during ion exchange chromatography. Most likely the effect is due to the extrinsic pathway inhibitor (EPI), also called lipoprotein-associated coagulation inhibitor (LACI), which has recently been shown to be released by heparin.

Antibodies↗
PubMed1991

Experimental studies on a recombinant hirudin, CGP 39393.

The in vitro anticoagulant activities of recombinant desulphatohirudin (r-hirudin) were studied in the activated partial thromboplastin time (APTT) and the thrombin generation test systems. In the APTT, at concentrations below 5 micrograms/ml, r-hirudin showed a dose-response curve. At concentrations above 5 micrograms/ml, the plasma became unclottable, but in the thrombin generation test, at least 10 micrograms/ml of r-hirudin was required for full inhibition of thrombin generation. The antithrombotic effect was assessed using a rabbit venous stasis model; 150 micrograms/kg r-hirudin completely prevented thrombus formation at 10 and 20 min stasis. At this full antithrombotic dose, the mean bleeding time ratio measured in a rabbit ear template model, was not prolonged over control values. At higher doses, the bleeding time ratios were higher than those observed for the same dosage of heparin. These data indicate that while r-hirudin is an effective antithrombotic agent, antithrombotic doses have to be carefully titrated to avoid excessive bleeding.

Animals↗
PubMed1991

Modelling sub-binomial variation in the frequency of sex combinations in litters of pigs.

In some samples of pig litters, the number of males per litter exhibits significant sub-binomial dispersion: there are fewer unisexual and more "sex-balanced" litters than expected under a binomial model. It is argued here that the explanation is that the sex of zygotes may be subject to hormonal control with the consequence that, within a litter, the zygotes do not all have the same probability of being male. This variation in probability is approximated by a quadratic function of the time during oestrus that a zygote is formed so as to parallel the variation in maternal hormone levels. Other explanations are examined briefly, but each seems to have serious weaknesses.

Analysis of Variance↗
PubMed1990

Potentiation of the antithrombotic action of dermatan sulphate by small amounts of heparin.

We have examined the effect in impairing thrombus formation of a preparation of dermatan sulphate (DS) alone and DS plus small amounts of unfractionated heparin (UFH). In rabbits given a dose of 150 micrograms/kg of DS alone, there was minimal reduction in serum-induced stasis thrombosis (Wessler model), with an overall score of 92.5% (100% = no impairment of thrombus formation). When the same dose of DS containing UFH was given (two different subgroups given DS containing 0.25 and 2.5% heparin by dry weight, respectively), the overall thrombus score was reduced to 60% (P less than 0.003), with no significant difference between the two subgroups. To achieve a comparable result with DS alone, a dose of 1 mg/kg was required. We conclude that very small amounts of UFH significantly enhance the antithrombotic action of DS, by a mechanism that has yet to be determined.

Animals↗
PubMed1989

Procoagulant activity of T lymphoblastoid cells in extrinsic and intrinsic coagulation systems.

We have measured the procoagulant activity (PCA) of four T lymphoblastoid cell lines (Jurkat, CEM, HSB-2 and Molt 4) as well as normal peripheral blood T lymphocytes, before and after stimulation with phytohaemagglutinin (PHA), using clotting and amidolytic methods. Of the four cell lines only one, Jurkat, gave enhanced PCA after stimulation with PHA. This activity was shown to be tissue factor-like by its dependence on factor VII in plasma and in an amidolytic assay with purified factors VII and X. Jurkat was also the only one of the four cell lines to secrete interleukin-2. All four cell lines promoted the generation of large amounts of thrombin in platelet-free plasma in glass tubes. This activity was dependent on the presence of plasma factor VIII, and was probably due to phospholipids in the cell membranes. Normal T lymphocytes gave intrinsic PCA in the thrombin generation test which was only 15% of that of the lymphoma cells. These results show that some T lymphocytes can develop PCA in both intrinsic and extrinsic systems and this should be taken into account in studies of the PCA of mixed leukocyte populations.

Blood Coagulation↗
PubMed1989

The relative antithrombotic effectiveness of heparin, a low molecular weight heparin, and a pentasaccharide fragment in an animal model.

The antithrombotic efficacy of unfractionated heparin (UFH), a low molecular weight heparin (LMWH) and a synthetic pentasaccharide (PENTA) has been compared in an animal model for stasis thrombosis. We have also compared the relative ability of these three agents to impair thrombin generation in vitro and in vivo, and measured their effects on anti-Xa activity and thrombin clotting times. UFH, LMWH and PENTA all had the capacity to impair thrombogenesis, although there were marked differences in their relative effectiveness. Reduction of thrombin generation to 20% of control values was closely correlated with the prevention of thrombosis after 20 minutes' stasis, but this was only achieved with UFH. The same dry weight dose of LMWH or PENTA reduced thrombin generation to about half control values, and neither significantly impaired thrombus formation after 20 minutes' stasis. Impaired thrombin generation correlated better than anti-Xa activity with prevention of stasis thrombosis. In this model, UFH was clearly superior to LMWH and PENTA as an antithrombotic agent.

Animals↗
PubMed1989

Animals' rights.

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Animal Welfare↗
PubMed1989

Effects of sulfated polysaccharides on inhibition of thrombus formation initiated by different stimuli.

To test the possibility that different doses of heparin or other sulfated polysaccharides are required to inhibit thrombosis initiated by different stimuli, we compared the effects of heparin (HEP), pentosan polysulfate (SP54) and dermatan sulfate (DS) on the inhibition of thrombus formation induced by either I) tissue thromboplastin; II) thrombin; or III) factor Xa. Inhibition of thrombus formation induced by the stimuli was measured in a rabbit jugular vein hypercoagulation/stasis model. First, we determined the minimum dose of each sulfated polysaccharide which inhibited tissue thromboplastin-induced thrombus formation by approximately 75%, and then compared the relative effectiveness of this dose to prevent thrombus formation initiated with the other two stimuli. HEP and SP54 were less effective when thrombin was the thrombogenic stimulus, while DS was more effective. HEP was the most effective agent when factor Xa was the stimulus. We conclude that the antithrombotic effectiveness of a given dose of a sulfated polysaccharide may vary depending on the stimulus which initiates thrombus formation.

Animals↗
PubMed1989

Effects of dermatan sulfate and heparin on inhibition of thrombus growth in vivo.

The effects of dermatan sulfate and heparin on inhibition of fibrin accretion onto existing thrombi as related to their ex vivo anticoagulant activity and abilities to inhibit increased prothrombin clearance induced by thrombi were investigated. Our results indicate that for equivalent anti-thrombin activities, dermatan sulfate is a more effective inhibitor of fibrin accretion onto existing thrombi than is heparin. These observations raise the possibility that in some clinical conditions dermatan sulfate, rather than heparin, may be a better antithrombotic agent of choice. This beneficial effect of dermatan sulfate appears to be unrelated to anti-factor Xa activity either endogenous to dermatan sulfate itself (which is unlikely since it does not catalyze factor Xa inhibition) or to anti-factor Xa activity associated with other glycosaminoglycans released into the circulation following dermatan sulfate administration since this activity is less than that associated with heparin treatment. It is more likely that dermatan sulfate mediates this beneficial effect by more effectively inhibiting thrombin within a thrombus than can heparin. This possibility is supported by the ability of dermatan sulfate to normalize prothrombin consumption in animals with existing thrombi.

Animals↗
PubMed1989

Adolescent smoking: attitudes, norms and parental influence.

The self-reported smoking habits and intentions of over 10,000 adolescents, aged 11 to 16 years, were related to a variety of attitudinal and normative variables. Current or previous smoking experience was a more important predictor of future intention to smoke than attitude or subjective norm (others' perceived tolerance of subjects' smoking). Parental opposition to smoking was a more important direct predictor of subjects' smoking intention than parental smoking behaviour.

Adolescent↗
PubMed1989

The emotional and play needs of the dying child.

At any particular moment, the doctor's goal is cure and the child's goal is self-pleasure. Recreation therapy helps the child meet this goal while moving toward the doctor's goal. When the doctor's goal can no longer be reached, recreation therapy can provide support to the child through the established relationship. The emotional and play needs of the dying child can be met.

Attitude to Death↗
PubMed1988

Heparin and bleeding: an association with lipase release.

The effects of four sulphated polysaccharides on bleeding time and lipase release in rabbits have been compared. Unfractionated heparin (UFH) and pentosan polysulphate both gave significant prolongation of bleeding times and high lipase release. Low molecular weight heparin had reduced effects on bleeding time and lipase release, while dermatan sulphate had no influence on either parameter. There was a highly significant correlation (r = 0.97) between these two measurements. These results suggest that the same structural features influence both the haemorrhagic and lipase-releasing properties of sulphated polysaccharides.

Animals↗