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Biomedical subjects

D Deykin

Publications and source records attributed to D Deykin.

At least 73 records · Page 4Linked to original sources
PubMed1983

Arachidonoyl transacylase in human platelets. Coenzyme A-independent transfer of arachidonate from phosphatidylcholine to lysoplasmenylethanolamine.

Human platelets contain an enzyme that catalyzes CoA-independent release of arachidonic acid from phosphatidylcholine with concomitant incorporation into plasmenylethanolamine. Addition of lysoplasmenylethanolamine (10-80 microM) to a crude membrane preparation of prelabeled platelets (0.24 mg of protein/ml) induces transfer of [3H]arachidonate from endogenous phosphatidylcholine to lysoplasmenylethanolamine (0.8 nmol of arachidonic acid/min/mg of protein). The transacylation reaction occurs in the absence of Ca2+, has a broad pH optimum from 7 to 8, is not affected by excess unlabeled arachidonic acid, and is inhibited by N-ethylmaleimide (0.2 mM) and Triton X-100 (0.1 mg/ml). The enzyme shows a high specificity toward the acyl donor (phosphatidylcholine), transfers fatty acids in the order: arachidonic greater than eicosatrienoic greater than oleic, and preferentially acylates lysoplasmenylethanolamine but also other lysophosphatides (lysophosphatidylethanolamine greater than lysophosphatidylserine greater than lysophosphatidylinositol = 0). Platelet acyltransferase, on the other hand, acylates ethanolamine lysophosphatides with free arachidonic acid in the order: lysophosphatidyl-ethanolamine greater than lysoplasmenylethanolamine. These results suggest that a distinct acylation mechanism exists for introduction of arachidonic acid into plasmalogen phosphatides. In stimulated platelets, the transacylase may play an additional role in the controlled release of esterified arachidonic acid for synthesis of the biologically active oxygenated metabolites.

Acyltransferases↗
PubMed1983

Uremic bleeding.

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Aged↗
PubMed1983

Arachidonic acid metabolism by platelets of differing size.

The relationship between mean platelet volume (MPV) and platelet arachidonic acid metabolism was examined by studying the ability of human platelets of different size to incorporate and metabolize tritiated arachidonic acid ([3H]AA). Platelet phospholipids were labelled with [3H]AA and the platelets were then fractionated into size-dependent subpopulations by counterflow centrifugation. The incorporation of [3H]AA increased through the fractions proportional to the MPV. After thrombin stimulation the per cent of total 3H-radioactivity released from the platelets decreased as the MPV increased. However, fractionation of the released 3H-radioactivity by HPLC (high performance liquid chromatography) demonstrated that MPV had no significant influence on the per cent of total platelet 3H-radioactivity released as cyclooxygenase products or as HETE (12-hydroxyeicosatetraenoic acid) but that the release of unmetabolized [3H]AA decreased as MPV increased. In separate experiments using unlabelled platelets the absolute release of thromboxane B2 (TXB2) after collagen- and thrombin-induced aggregation was measured by radioimmunoassay and was found to increase in proportion to the MPV. These results demonstrate that the release of arachidonic acid metabolites is qualitatively similar in platelets of different size. However, the absolute ability of platelets to incorporate arachidonic acid, convert it to active metabolites and release them is proportional to their volume. The ability of platelets to release unmetabolized arachidonic acid varies inversely with their MPV.

12-Hydroxy-5,8,10,14-eicosatetraenoic Acid↗
PubMed1983

Platelet size as a determinant of platelet function.

The relationship between MPV and platelet function was studied in human platelet subpopulations separated on the basis of size and counterflow centrifugation. The original platelet population and five size-dependent platelet fractions were suspended in buffer or autologous PPP at a platelet count of 2 x 10(8)/ml. Collagen (10 micrograms/ml)-induced aggregation showed a significant negative correlation between MPV and onset of aggregation and positive correlations between the MPV and the rate of extent of aggregation. Thrombin stimulation (1 U/ml) demonstrated similar relationships between MPV and the rate of extent of aggregation. In contrast, ristocetin-induced platelet agglutination occurred at a similar rate and extent in all fractions. To quantitate further the differential response of the platelets, we measured the content and release of ATP and beta-TG. There was a significant correlation between MPV and both ATP and beta-TG content, and a progressive increase in the absolute release of ATP and beta-TG was associated with the increase in MPV through the fractions after stimulation. However, the percent release of total ATP and beta-TG was similar in all fractions. Our data indicate that the intrinsic function of platelets of different sizes is similar but that the absolute ability of platelets to affect their environment, as measured by aggregation and total release of granular content, correlates with their size.

Adenosine Triphosphate↗
PubMed1982

Effect of membrane cholesterol on phospholipid metabolism in thrombin-stimulated platelets. Enhanced activation of platelet phospholipase(s) for liberation of arachidonic acid.

The cholesterol to phospholipid mole ratio (C/PL) of human platelets was increased 1.3-fold or maintained at a normal value by incubating platelets with sonicated dispersions of cholesterol and phosphatidylcholine (PC) (C/PL = 3 or 1, respectively). Thrombin-induced mobilization of [3H]arachidonic acid from prelabeled phospholipids and subsequent formation of labeled cyclo-oxygenase and lipoxygenase products were increased in cholesterol-enriched platelets as a function of thrombin concentration. Elevated platelet cholesterol content affected thrombin-induced changes in platelet phospholipids: (a) hydrolysis of PC was more sensitive to thrombin and was markedly enhanced over a wide range of thrombin concentrations (0.1-2 units/ml); (b) hydrolysis of phosphatidylinositol (PI) was increased at thrombin concentrations greater than or equal to 0.2 unit/ml. Increased metabolism of [3H]arachidonic acid in stimulated cholesterol-enriched platelets was due to loss of [3H]arachidonate from PC at 0.1 unit/ml of thrombin. At higher thrombin concentrations (0.2-2 units/ml) it reflected enhanced hydrolysis of predominantly PC, but also PI. We conclude that cholesterol, possibly through its effect on platelet lipid organization, influences arachidonic acid metabolism in stimulated plates by promoting enhanced activity of platelet phospholipase(s) for liberation of arachidonic acid.

Arachidonic Acids↗
PubMed1982

Current status of anticoagulant therapy.

Anticoagulant therapy has stood the test to time. Full-dose heparin and warfarin prevent recurring pulmonary embolism and deep venous thrombosis. Their use is indicated in patients who have experienced venous thromboembolism unless contraindications are compelling. Low-dose heparin is successful in preventing the initial episode of venous thrombosis in most patients at high risk for the development of thrombophlebitis. Warfarin reduces the incidence of systemic embolization in patients with heart disease and atrial fibrillation and in patients with artificial heart valves. Evidence is accumulating to suggest that warfarin may still retain an important role in the management of patients with myocardial infarction. However, bleeding remains an inevitable risk in patients receiving anticoagulant therapy. The risk, however, can be diminished when both the physician and patient understand the mechanism of action of the drugs and the factors that predispose to bleeding.

Heart Diseases↗
PubMed1981

The activation of phosphatidylinositol-hydrolyzing phospholipase A2 during prostaglandin synthesis in transformed mouse BALB/3T3 cells.

To investigate the type of phospholipase activated by agents that stimulate prostaglandin synthesis, we used transformed mouse cells whose phospholipids were doubly labeled with [14C]inositol and [3H]arachidonic acid. [14C]Inositol was incorporated mostly into the phosphatidylinositol and [3H]arachidonic acid was distributed into the various phospholipids. When these cells were incubated with bradykinin, a stimulator of prostaglandin synthesis, the release of 3H radioactivity from cellular phospholipids and the synthesis of prostaglandin were initiated within seconds and reached a maximum in 40 to 70 s. Analysis of the intracellular lipids revealed a concomitant increase of radioactivity associated with lysophosphatidylinositol, which was detectable within 5 s of incubation with bradykinin and reached a maximum between 40 and 70 s. Lysophosphatidylinositol which could be formed either from a phospholipase A1 or phospholipase A2 reaction, was identified by its chromatographic properties and conversion to glycerophosphorylinositol. We found that the 3H/14C ratio of purified lysophosphatidylinositol was 1/11 of that of phosphatidylinositol, which indicated that lysophosphatidylinositol formed in response to bradykinin is 1-acyl-sn-glycero-3-phosphorylinositol and most probably is formed from a phospholipase A2 deacylation of phosphatidylinositol (a phospholipase A1 deacylation would result in the formation of lysophosphatidylinositol of a 3H/14C ratio similar to phosphatidylinositol). Furthermore, we did not detect between control and stimulated cells any significant difference in the level of several phospholipase C metabolites including inositol phosphate, diglyceride, and phosphatidic acid. These results suggest that phospholipase C is probably not activated. The formation of lysophosphatidylinositol was also stimulated by thrombin and ionophore A23187, both activators of prostaglandin synthesis. Dexamethasone, a lipase inhibitor, inhibited the appearance of lysophosphatidylinositol, whereas aspirin and low concentrations of indomethacin, the cyclooxygenase inhibitor, did not inhibit. The results presented in ths paper provide evidence that a phospholipase A2-hydrolyzing phosphatidylinositol is activated when intact cells are stimulated for prostaglandin synthesis.

Animals↗
PubMed1981

Analysis of factor VIII coagulant antigen in normal, thrombin-treated, and hemophilic plasma.

The relationship between Factor VIII coagulant antigen (VIII:CAg) and Factor VIII-associated von Willebrand factor (VIII:vWF), and the effect of thrombin on VIII:CAg have been determined in plasma by using complexes of VIII:CAg and 125I-labeled human anti-VIII:CAg-Fab. Antibody-treated plasma samples were electrophoresed on NaDodSO4/polyacrylamide agarose gels and analyzed by autoradiography. The major VIII:CAg-125I-labeled Fab complex that persisted in NaDodSO4 had Mr 3.2 x 10(5). This Mr value was confirmed by column chromatography and sucrose density centrifugation and is presumed to reflect a free VIII:CAg of Mr 2.7 x 10(5). Minor bands were also present on autoradiograms of normal plasma corresponding to Mr values of 2.5, 1.85, and 1.7 x 10(5) (free VIII:CAg related proteins with Mr values of 2.0, 1.35, and 1.2 x 10(5), respectively). None of the VIII:CAg bands was present in plasma samples from five patients with severe hemophilia A. No radioactivity was associated with VIII:vWF multimers on NaDodSO4 gels. Thrombin treatment of normal plasma eliminated the radioactive band at 3.2 x 10(5) and increased the intensity of a band of Mr 1.7 x 10(5). Generation of this presumed VIII:CAg fragment of Mr is approximately equal to 1.2 x 10(5) coincided with a thrombin-induced increase in Factor VIII coagulant activity. These data demonstrate that the form of VIII:CAg detected in normal plasma is not covalently linked to VIII:vWF multimers and is absent in plasma from five hemophilia A patients. Thrombin-induced proteolysis of VIII:CAg can be detected in microliter quantities of normal plasma.

Antigen-Antibody Reactions↗
PubMed1981

Autoimmune thrombocytopenic purpura-like syndrome in a patient with head and neck cancer.

We report a case of presumed autoimmune thrombocytopenic purpura in a patient with squamous cell carcinoma of the neck. A review of the literature on the association of autoimmune thrombocytopenic purpura and solid tumors is presented. Autoimmune-like thrombocytopenia should be considered when patients with head and neck carcinoma present with an acute hemorrhage diathesis.

Aged↗
PubMed1980

Treatment of the bleeding tendency in uremia with cryoprecipitate.

We gave cryoprecipitate to six patients with uremia and bleeding times prolonged to more than 15 minutes. After the infusion, all patients had shortened bleeding times; the times of five became normal. In four patients control of major bleeding episodes was attained, and five underwent major surgical or invasive procedures, with good hemostasis. After infusion the time before the nadir of the bleeding time was reached was between one and 12 hours. The bleeding time returned to pretreatment levels by 24 hours after infusion in five patients, and by 36 hours in the other patient. Platelet-aggregation studies before infusion gave normal results in three patients and abnormal results in three. There wasno change after infusion. Before infusion, levels of Factor VIII coagulant activity and Factor VIII von Willebrand activity were normal, Factor VIII-related antigen was increased, and crossed immunoelectrophoresis of Factor VIII-related antigen was normal. Our findings suggest that cryoprecipitate can temporarily correct the bleeding tendency in patients with uremia.

Adult↗
PubMed1980

Tranylcypromine and 15-hydroperoxyarachidonate affect arachidonic acid release in addition to inhibition of prostacyclin synthesis in calf aortic endothelial cells.

In this paper, we examined the effect of two known inhibitors of prostacyclin synthetase, tranylcypromine and 15-hydroperoxyarachidonate, on bradykinin-stimulated prostacyclin synthesis and arachidonic acid release from cellular phospholipids in endothelial cells derived from calf aorta. These two inhibitors inhibit prostacyclin synthesis stimulated by bradykinin, arachidonic acid, and ionophore A23187. However, these two inhibitors also affect the release of arachidonic acid from cells. Using cells prelabeled with [3H]arachidonic acid, we found that bradykinin-stimulated arachidonic acid release is severely inhibited by tranylcypromine (500 microgram/ml) but is stimulated by 15-hydroxyperoxyarachidonate at a concentration as low as 1 microgram/ml. We also found that 15-hydroperoxyarachidonate inhibits not only prostacyclin formation but also prostaglandin formation from the released arachidonic acid. Under the conditions used, these two compounds have no effects on the cell viability as judged by trypan blue exclusion test. We conclude that tranylcypromine and 15-hydroperoxyarachidonate not only inhibit prostacyclin synthesis but also affect other steps in the metabolism of arachidonic acid in whole cells.

Animals↗
PubMed1980

Heparin induced thrombocytopenia: a prospective study.

Thrombocytopenia occurred in 11.6% of 43 patients prospectively randomized to receive either bovine lung or porcine mucosal heparin. Four patients received bovine heparin and developed mild to moderate thrombocytopenia after eight to twelve days which resolved when therapy was stopped in one to six days. One patient received porcine heparin and developed mild thrombocytopenia after four days. The thrombocytopenia resolved in one day in spite of continued heparin therapy. Serial blood samples from the five thrombocytopenic patients were studied for their in vitro effect upon normal platelets. These samples induced a high release of serotonin from normal platelets or caused normal platelets to aggregate in the presence of additional heparin. Release or aggregation coincided with or occurred shortly after nadir platelet counts were reached and returned toward normal following cessation of heparin. Our data constitute the first prospective study of heparin induced thrombocytopenia in which serial blood samples were studied before, during and following the onset of thrombocytopenia. They strongly support the presence of a heparin dependent co-factor, presumably an antibody, as the cause for thrombocytopenia.

Animals↗