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J C Hoak

Publications and source records attributed to J C Hoak.

At least 37 records · Page 2Linked to original sources
PubMed1982

Enrichment of human platelet phospholipids with linoleic acid diminishes thromboxane release.

We have investigated whether exposure of human platelets to elevated concentrations of linoleic acid, the principal dietary polyunsaturate, would influence platelet thromboxane A2 release. Platelets were incubated with albumin-bound linoleic acid at 30 degrees C for 24 h, with prostaglandin E1 added to prevent aggregation. The linoleic acid supplemented platelets released, on average, 50% less thromboxane A2 in response to stimulation with thrombin than corresponding control platelets. Other fatty acids were without appreciable effect. The inhibition of thrombin-stimulated thromboxane A2 release was dependent on the time and temperature of incubation, as well as on the concentration of added linoleic acid. Supplementation increased the amount of linoleic acid in the platelet phospholipids, but the arachidonic acid content of the phospholipids was reduced. [1-14C]Linoleic acid was not converted to arachidonic acid by the platelets. Linoleic acid was released exclusively from the inositol phosphoglycerides when the enriched platelets were stimulated with thrombin. The linoleate-enriched platelets converted less [1-14C]arachidonic acid to all prostaglandin products, suggesting that the platelet cyclooxygenase was partially inhibited.

Arachidonic Acid↗
PubMed1982

Role of Ca2+ and cyclic AMP in the regulation of the production of prostacyclin by the vascular endothelium.

Incubation of primary monolayer cultures of human umbilical vein endothelial cells with buffer, thrombin (0.5 unit/ml), ionophore A23187 (10 microM), arachidonic acid (20 microM), prostaglandin H2 (PGH2) (4 microM) resulted in prostacyclin (PGI2) production in nanomolar quantities to the extent of 36 +/- 2, 276 +/- 13, 485 +/- 32, 533 +/- 22, and 532 +/- 22, respectively, as measured by radioimmunoassay of 6-keto-PGF alpha. Preincubation of the endothelium with 1 mM 8-(N,N-diethylamino)-octyl-3,4,5-trimethoxybenzoate, an antagonist of cytoplasmic Ca2+, or with 4 mM 1-methyl-3-isobutylxanthine (MIX), an inhibitor of cyclic nucleotide phosphodiesterase activity, blocked PGI2 release induced by thrombin or A23187, decreased arachidonic acid-induced release by approximately 50%, but had no effect on PGH2-induced release. Radioimmunoassay of cAMP in the endothelium showed that the basal level (1.85 +/- 0.14 pmol of cAMP per 4.5 x 10(5) cells) was increased by an average of 3.9-fold with 4 mM MIX. PGI2 (0.4 microM) had no significant effect on cAMP levels in the absence of MIX, but caused a 2-fold increase with 4 mM MIX. The findings suggest that: (i) the stimulation of PGI2 biosynthesis is mediated by Ca2+, (ii) increased cAMP inhibits PGI2 production, and (iii) cAMP phosphodiesterase activity modulates PGI2-induced increases in the intracellular concentration of cAMP.

3',5'-Cyclic-AMP Phosphodiesterases↗
PubMed1982

Role of the vascular endothelium.

A possible explanation for the non-thrombogenic effect of the endothelium is the presence of prostacyclin, (PGI2), the potent inhibitor of platelet aggregation and adherence, which is produced and released by the endothelium in response to various stimuli. Removal of PGI2 from the endothelium did not increase baseline platelet adherence, but did increase thrombin-induced platelet adherence from 4 to 60%. Additions of exogenous PGI2 at low concentrations reversed the enhanced thrombin-induced platelet adherence under these conditions. Although it is unlikely that prostacyclin is the sole factor regulating platelet adherence to the endothelium, it appears to play a major role in the interaction of platelets with components of the blood vessel wall. Conditions which predispose to adherence of platelets to the vessel wall may involve entrapment of tumor cells and lead to metastasis formation. Whether prostacyclin and other factors involved in the non-thrombogenic character of the vascular endothelium provide a significant defense against attachment of tumor cells is not known, but the potential for such a primary or secondary role clearly exists. In our studies, prostacyclin did not appear to influence the adherence of Raji lymphoma cells to the endothelium. Additional studies are indicated to correlate adherence of tumor cells to the vascular wall with their potential for formation of metastatic lesions.

1-Methyl-3-isobutylxanthine↗
PubMed1982

Contribution of a platelet component to endothelial prostacyclin production despite inhibition of platelet cyclooxygenase activity.

Platelets aggregated with low concentrations of thrombin enhanced prostacyclin release from umbilical vein endothelium, which had an active cyclooxygenase. This result cannot be explained solely by an effect of thrombin on the endothelium or by transfer of the endoperoxide PGH2 from platelets to the endothelium. The quantity of prostacyclin released is sufficient to alter platelet adherence to umbilical vein endothelium in the presence of thrombin.

6-Ketoprostaglandin F1 alpha↗
PubMed1981

Role of the vascular endothelium.

The intact vascular endothelial surface is considered to be "non-thrombogenic", and blood platelets usually fail to adhere to ti. In this role, the endothelium serves to maintain the integrity of the vascular system by preventing the escape of blood and by preventing the build-up of solid thrombus within the vessel, which would compromise blood flow. A possible explanation for the non-thrombogenic effect of the endothelium is the presence of prostacyclin (PGI2), the potent inhibitor of platelet aggregation and adherence, which is produced and released by the endothelium in response to various stimuli. Removal of PGI2 from the endothelium by four different methods did not increase baseline platelet adherence, but did increase thrombin-induced platelet adherence from 4 to 60%. Addition of exogenous PGI2, at low concentrations reversed the enhanced thrombin-induced platelet adherence under these conditions. Although it is unlikely that prostacyclin is the sole factor regulating platelet adherence to the endothelium, it appears to play a major role in the interaction of platelets with components of the blood vessel wall.

Animals↗
PubMed1981

Massive fatal pulmonary emboli with fibrinolytic therapy.

A case is described in which massive fatal pulmonary emboli followed the initiation of thrombolytic therapy. Several important issues regarding anticoagulation and fibrinolytic therapy are addressed, including the possibility of anticoagulant failure and the risks of using fibrinolytic therapy in the setting of recent and remote thrombotic disease.

Adult↗
PubMed1981

Utilization of arachidonic and linoleic acids by cultured human endothelial cells.

When cultured human umbilical vein endothelial cells are supplemented with linoleic acid, the arachidonic acid content of the cellular phospholipids is reduced approximately 35%. Most of the fatty acid compositional change occurs during the first 24 h. One factor responsible for this effect is the inability of the endothelial cells to convert appreciable amounts of linoleic to arachidonic acid, due to a fatty acid delta 6-desaturase deficiency. By contrast, these endothelial cultures contain delta 5- and delta 9-desaturase activity and are able to elongate long-chain polyunsaturated fatty acids. The other factor that contributes to the decrease in arachidonic acid is that high concentrations of linoleic acid reduce the incorporation of arachidonate into cellular phospholipids. Stearic acid, a long-chain saturate, does not produce any reduction, whereas eicosatrienoic acid is an even more effective inhibitor than linoleic acid. In spite of the fact that high concentrations of these polyunsaturates produced inhibition, the endothelial cells were found to efficiently incorporate exogenous arachidonic acid into cellular phospholipids and triglycerides. This may serve to compensate for the inability of these cells to synthesize arachidonic acid from linoleic acid. These findings suggest that the endothelium obtains arachidonic acid from an extracellular source, that this cannot be provided in the form of linoleic acid and, in fact, that high concentrations of linoleic acid actually may interfere with the ability of the endothelium to maintain an adequate supply of intracellular arachidonic acid.

Arachidonic Acid↗
PubMed1981

Prostacyclin release from cultured and ex vivo bovine vascular endothelium. Studies with thrombin, arachidonic acid, and ionophore A23187.

Prostacyclin release from systemic and pulmonary endothelium has been evaluated in cultured cell monolayers and in an ex vivo vascular segment model in which the endothelium remains in contact with subendothelial structures. The effect of exposure to arachidonic acid, ionophore A23187, and thrombin on prostacyclin release has been assessed. Arachidonic acid elicited prostacyclin release in a dose-dependent fashion. Ionophore also stimulated bovine systemic endothelium to release prostacyclin. Thrombin-endothelial cell interactions have been examined extensively. Unlike umbilical venous endothelium, systemic and pulmonary bovine endothelium did not release prostacyclin following exposure to thrombin. Exposure to thrombin also failed to evoke the release of tritiated arachidonate metabolites from the bovine endothelial cell preparations. The presence of high affinity binding sites for thrombin (KD = 9.5 X 10(-9) M) on the bovine endothelium suggests that either thrombin binding is causally unrelated to prostacyclin release or that the bovine cells lack mediators required for thrombin to exert its effect.

Animals↗
PubMed1981

Comparative effect of ibuprofen on endothelial and platelet prostaglandin synthesis.

Ibuprofen (Motrin) decreases infarct size in animal models of myocardial infarction. Inasmuch as this effect might be related to the inhibitory effect of ibuprofen on platelet function, we have evaluated its effect on platelet and endothelial prostaglandin synthesis. Human umbilical vein endothelial cultures and washed human platelets were studied. Thromboxane (TX)A2 was determined by radioimmunoassay for its stable and product TXB2 and prostacyclin was determined by radioimmunoassay for its stable end product 6-keto-prostaglandin F1 alpha. At all concentrations of ibuprofen tested, platelet TXA2 and endothelial prostacyclin synthesis were inhibited to a similar degree. Unlike aspirin, the effect of ibuprofen on prostaglandin synthesis was rapidly reversible in both endothelial and platelet systems after removal of the drug. Ibuprofen was also shown to interfere with the irreversible inhibitory effect of aspirin, suggesting that ibuprofen and aspirin might compete for binding by the cyclooxygenase. Inhibition of endothelial and platelet prostaglandin synthesis was nearly complete with 100 microM concentrations of aspirin (100%) and ibuprofen (99%). Thrombin-stimulated platelet adherence to endothelial monolayers was related inversely to the amount of prostacyclin produced by the endothelium. Adherence was maximal at concentrations (100 microM) of ibuprofen and aspirin producing near complete inhibition of prostaglandin synthesis. Maximal adherence with both drugs was comparable (28 vs. 31%). Ibuprofen showed no preferential inhibitory effect on TXA2 synthesis and, at a 100 microM concentration, was as effective as aspirin in the systems studied.

6-Ketoprostaglandin F1 alpha↗
PubMed1981

Pulmonary embolism in patients with acute leukemia and severe thrombocytopenia.

While pulmonary thromboembolism has been reported in patients with acute leukemia complicated by severe thrombocytopenia, it has been studied infrequently and its pathogenesis remains imprecisely understood. Findings of 80 consecutive autopsies of patients with acute leukemia showed that three had pulmonary thromboembolism. All three patients had been severely thrombocytopenic and had received numerous platelet transfusions. Serial sections of thrombi were evaluated with electron microscopy. In no instance were platelet aggregates detected. However, Candida organisms were prominent in thrombotic specimens from each patient. These findings suggest that thromboembolism in such patients may involve occult fungal infection. Because pulmonary thromboembolism can complicate the course of acute leukemia and severe thrombocytopenia, it should be considered when clinical data suggest its occurrence.

Acute Disease↗
PubMed1980

Binding of thrombin to cultured human endothelial cells. Nonequilibrium aspects.

The long-term incubation of 125I-thrombin with cultured human endothelial cells is studied and compared to the previously described rapid equilibrium binding in this system (Awbrey, B. J., Hoak, J. C., and Owen, W. G. (1979) J. Biol. Chem. 254, 4092-4095). Following rapid initial binding of thrombin, a much slower association of thrombin with endothelium is seen. As opposed to equilibrium binding, this process is 1) irreversible, 2) active-site specific, and 3) associated with covalent linkage to an Mr 30,000 protein. In addition this nonequilibrium binding appears unrelated to high-affinity equilibrium binding since blocking the high-affinity binding sites with diisopropylphosphoryl thrombin has no effect on nonequilibrium binding. The physiological role of this process is unknown.

Cells, Cultured↗
PubMed1980

Arterial platelet accumulation in experimental hypercholesterolemia.

Accumulation of arterial platelets was calculated from 51Cr radioactivity in the intima-inner media of flushed, perfuse-fixed aortas and branch vessels of cynomolgus monkeys 48 hours after labeling of the blood platelets. In normo-cholesterolemic controls the radioactivity per square centimeter of tissue was consistently higher in aortic branching sites (circumostial aorta) than in the remainder of the aorta. In monkeys given 10 and 100 days of hypercholesterolemic diet radioactivity rose in circumostial aorta in proportion to increases in streaks and in areas of Evans blue uptake. In branch artery inner wall, where intimal changes were minimal and usually absent, counts were significantly greater in animals given 100 days of hypercholesterolemic diet than in controls. After 10 days of hypercholesterolemic diet the mean radioactivity in aortic branch artery inner wall uniformly exceeded control values, but usually nonsignificantly, permitting the speculation that changes in platelet-intima interactions may occur in widespread fashion throughout the arterial tree very early in hypercholesterolemia when lesion formation is incipient or absent.

Animals↗
PubMed1980

Effect of fatty acid modification on prostacyclin production by cultured human endothelial cells.

We have investigated whether changes in cellular fatty acid saturation can influence prostacyclin (PGI2) production by cultured human umbilical vein endothelial cells. As compared to control cells, those enriched with linoleic acid released 60--75% less PGI2 in response to thrombin or the calcium ionophore A23187. A similar but considerably smaller effect was observed when the cells were enriched with oleic or linolenic acid, but no reduction occurred with palmitic or linoelaidic acids. Some reduction in PGI2 release was noted as early as 1 h after exposure to linoleic acid. When the culture medium was supplemented with linoleic acid, the cell phospholipids contained four to five times more linoleate and 25--40% less arachidonate. These changes were most marked in the choline and serine plus inositol phosphoglyceride fractions. When the fatty acid composition of the cells enriched with linoleic acid was allowed to revert, there was a progressive increase in the capacity of the cells to release PGI2 in response to thrombin. The increase correlated with a reduction in linoleate content of the cell lipids, but there was no change in arachidonate content. This suggests that linoleic acid may act as an inhibitor of PGI2 production. The cultured endothelial cells were also able to produce PGI2 directly from added arachidonic acid. As the arachidonic acid concentration of the medium was raised, PGI2 formation by the linoleate-enriched cells increased relative to control cells, suggesting that the inhibition produced by linoleic acid may be competitive.

Arachidonic Acids↗
PubMed1980

Differential binding of insulin to human arterial and venous endothelial cells in primary culture.

The properties of 125I-insulin binding were assessed in endothelial cells prepared from the veins and the arteries of human umbilical cords. The endothelial nature of both the natural and venous cultures were documented by the presence of characteristic endothelial features, including Weibel-Palade bodies, factor VIII antigen, and morphology. Both arterial and venous cells possessed typical receptors for insulin on the basis of specificity of binding, curvilinear Scatchard plots, affinity profiles, pH dependency, and dissociation kinetics. Arterial cells bound at least 2.5 times more insulin than did venous cells, whether studied at 4 h, 24 h, or 72 h after in vitro plating. We conclude that (1) specific receptors for insulin are present on human arterial as well as human venous endothelial cells and (2) the concentration of insulin receptors varies among endothelial cells derived from different vascular sources.

Endothelium↗