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Biomedical subjects

J C Hoak

Publications and source records attributed to J C Hoak.

At least 55 records · Page 3Linked to original sources
PubMed1980

Interaction of thrombin and platelets with the vascular endothelium.

Thrombin is a potent stimulus for prostacyclin (PGI2) release from the vascular endothelium. Treatment of the endothelium with high concentrations of aspirin to block PGI2 formation was associated with increased platelet adherence in a system employing thrombin and 51Cr-labeled platelets. Addition of exogenous PGI2 to the aspirin-treated endothelium restored platelet adherence to the low baseline values. After an initial exposure of the endothelium to thrombin, the cultured endothelium was unable to respond to a second thrombin stimulus with release of PGI2. During this refractory period, the absence of PGI2 was associated with increased platelet adherence. Thus thrombin, an active coagulant and thrombogenic substance, has the capability to release PGI2, the most potent inhibitor of platelet aggregation known to exist in vivo.

Aspirin↗
PubMed1979

Binding of human thrombin to cultured human endothelial cells.

Binding of thrombin to monolayer cultures of human umbilical vein endothelium is studied. Binding is measured as inhibition by unlabeled ligand of the binding of 125I-thrombin to the cells. Radioactivity bound to cultures at equilibrium is measured after draining but not washing the cells. To correct for unremoved supernatant, 131I-albumin is included as a second label in the medium. Equilibrium between bound and free thrombin is attained within 1 min, and Scatchard analysis indicates a population of approximately 3 x 10(3) sites/cell with a dissociation constant of 10(-10) M, and a larger population with a dissociation constant greater than 10(-8) M. The two populations of sites are also indicated by a biphasic dissociation of bound label. Thrombin inactivated with diisopropyl fluorophosphate binds to the same receptor, with an affinity similar to that of active thrombin. Binding is unaffected by albumin (an acidic protein) and cytochrome c (a basic protein). Cultures of umbilical cord smooth muscle and fibroblasts bind thrombin at least 100 times more weakly than endothelium, and no binding to erythrocytes or a monolayer culture of mouse neuroblastoma is detected.

Cells, Cultured↗
PubMed1979

The effects of albumin bound fatty acids on the platelet inhibitory function of human endothelial cells.

This study was carried out to evaluate the effects of albumin-bound fatty acids on the anti-platelet effects of endothelial cells. Primary cultures of human endothelial cells (ECM), grown in confluent monolayers, were incubated with plasma or growth medium enriched with albumin-bound fatty acids (FA) for 2-20 h. The effects of ECM on ADP-induced platelet aggregation (PA) and collagen-induced PA and prostaglandin synthesis in platelet-rich plasma were tested. ECM released an inhibitor of platelet reactions which resembled the activity of PGI2 (prostacyclin). The inhibitory activity was increased by preincubation of ECM with arachidonic acid (AA). A moderate decrease of the activity was obtained by incubation with long-chain saturated, monoenoic and dienoic unsaturated fatty acids. A pronounced decrease of the inhibitor was obtained by incubation with di-homo-gamma-linolenic acid (DHLA). Paired combinations of AA with the other fatty acids in the incubation medium partially restored the inhibitory activity obtained by the separate FA. The stimulation of the inhibitor by AA was dose dependent and high concentrations of AA reduced this activity. The present study indicates that the quantity and quality of the plasma free fatty acids can affect the endothelial cells' ability to act as a non-thrombogenic surface.

Blood Platelets↗
PubMed1979

Inhibition of prostacyclin by treatment of endothelium with aspirin. Correlation with platelet adherence.

Aspirin treatment of cultured endothelial cells from the umbilical vein increased the adherence of 51Cr-platelets when thrombin was present. If the cyclooxygenase activity of endothelium was inhibited by aspirin, as it is in the platelet, reduction of endogenous prostacyclin (PGI2) production could have been responsible. By correlating thrombin-induced adherence of platelets to endothelial monolayers with PGI2 release (as measured by radioimmunoassay for 6-keto-prostaglandin FI1 alpha [6-keto-PGF1 alpha]), we have demonstrated an inverse relationship between platelet adherence and PGI2 levels. Untreated endothelial monolayers exposed to thrombin and platelets resulted in 4% platelet adherence and 107 nM 6-keto-PGF1 alpha. With 0.1 mM aspirin treatment, which is known to block platelet cyclooxygenase, adherence was 5% and 6-keto-PGF1 alpha decreased to 45 nM. Increasing the aspirin concentration to 1 mM resulted in 44% adherence and less than 3 nM 6-keto-PGF1 alpha. When 25 nM exogenous PGI2 was added to 1 mM aspirin-treated endothelium, adherence returned to 5%. The increase in thrombin-induced platelet adherence to 1 mM aspirin-treated monolayers was reversed 2 h after removal of the aspirin solution. 6-Keto-PGF1 alpha returned to 37% of the untreated monolayer value. Recovery from the aspirin effect did not occur when cycloheximide, an inhibitor of protein synthesis, was present during the 2-h period.

Aspirin↗
PubMed1979

Platelet-endothelial cell interactions.

We are in an era in which there has been a rapid accumulation of new information about the endothelium and the interactions of platelets with the vessel wall. The decade of the 70s could aptly be designated as the "prostaglandin and endothelium period." One can only speculate that the future will be equally interesting and challenging. It is quite possible that discoveries of congenital and acquired defects of the endothelium will parallel those already described for the platelet and coagulation factors. What is currently looked upon today as a baffling and frustrating case of resistant thrombosis by the clinician may be unraveled tomorrow by the talented and creative investigator who can develop better approaches to the study of the endothelium and platelet interactions with the vessel wall.

Animals↗
PubMed1978

The inhibitory effect of aspirin on human endothelial cells.

Human endothelial cell monolayers prepared from umbilical veins have been incubated with aspirin (1--2 mM) dissolved in Hepes modified solution and in platelet-rich plasma. They have also been incubated with plasma prepared from subjects before and after intake of aspirin giving a mean plasma concentration of 0.5 mM. The effects of the endothelial cells on ADP and collagen-induced platelet aggregation and malondialdehyde production in platelet-rich plasma have been tested. The endothelial cells had a spontaneous inhibitory effect on all three parameters. This effect was abolished when the cells were incubated with aspirin dissolved in MHS for 20 min and the increase in effect observed when platelet-rich plasma was incubated with endothelial cells for a period of 30 min was similarly inhibited when aspirin was dissolved in plasma or when plasma prepared from subjects who had taken aspirin were used. Aspirin had no inhibitory effect on prostacyclin (PGI2) with regard to the effect of PGI2 on platelets. On the contrary, the two compounds had an additive inhibitory effect on platelet aggregation induced by ADP and collagen. These findings should be considered with regard to the use of aspirin as an antithrombotic agent.

Aspirin↗
PubMed1978

Erroneous clinical diagnosis of leg vein thrombosis in women on oral contraceptives.

Most studies demonstrating an increased risk of venous thromboembolism in women on oral contraceptives are based on clinical manifestations of the disease. Because of the fallibility of the clinical diagnosis of suspected leg vein thrombosis, Doppler ultrasonic evaluation (with a 93% accuracy compared to venography) was performed for clinical manifestations in deep vein thrombosis in 54 women taking birth control pills and 75 women of similar age who were not on contraceptives. The clinical diagnosis was confirmed by Doppler in only 16.7% of the women taking contraceptives and 30.7% of women not taking contraceptives (P = 0.052). This study suggests that the clinical diagnosis of leg vein thrombosis is frequently erroneous, particularly in women taking oral contraceptives. Future investigations reporting venous thromboembolism associated with oral contraceptives should be based on diagnoses validated by accurate objective techniques.

Adolescent↗
PubMed1978

The effects of glucocorticoids on cultured human endothelial cells.

The effects of hydrocortisone, dexamethasone and prednisone on the morphology, replication, DNA synthesis, cell protein content and protein synthesis of cultured, human endothelial cells were evaluated. After culturing the cells with these glucocorticoids for 24-48 h, the cells covered a greater portion of the culture surface area. The mean surface area of the individual endothelial cell treated with glucocorticoids was 1.53 times greater than that of the untreated control endothelial cell. When compared with controls, the endothelial cover provided by the cells treated with glucocorticoids was more extensive and in many instances covered the entire culture surface. The change in morphology was associated with an increase in protein synthesis and protein content of the cells without an increase in DNA synthesis or cellular replication. Dexamethasone was approximately 10-fold more effective than hydrocortisone, while prednisone was the least effective. Aldosterone, DOCA, testosterone, progesterone, oestradiol and oestriol were ineffective. These studies indicate that glucocorticoids can alter the morphology and biochemistry of cultured endothelial cells and may have implications for the effects of steroids in the treatment of thrombocytopenic states and vascular disorders in man.

Cells, Cultured↗
PubMed1978

The influence of age, sex, and the use of oral contraceptives on the inhibitory effects of endothelial cells and PGI2 (prostacyclin) on platelet function.

The inhibitory effects of human endothelial cells (ECM) and PGI2 (prostacyclin) on platelet function have been examined in 60 healthy subjects. 5 groups were studied. I. 10 women (19-33 yrs.); II. 10 women (21-31 yrs.) using combined oral contraceptives; III. 10 postmenopausal women (45-66 yrs.); IV. 20 men (24-48 yrs.) and V. 10 men (48-71 yrs.). Spontaneous platelet aggregation in platelet-rich plasma (PRP) was commonly observed in groups II, III, and V. This was prevented when PRP was incubated with ECM, aspirin (ASA), or PGI2. ADP-induced platelet aggregation (PA) was always reduced by ECM, but significantly less in groups II and III. Collagen-induced PA was inhibited by ECM, but less in groups I, II, III and V than in young men (IV). ECM significantly reduced collagen-induced prostaglandin (MDA) production in platelets. Again, the inhibitory effect was significantly reduced in groups II and III. Platelet factor 3 activity, measured after exposure of PRP to ADP, was significantly reduced by ECM, but was significantly less in groups II, III, and V than in group I. Less of an inhibitory, effect of PGI2 upon ADP-induced PA was shown by all groups of females than by the two groups of males.

Adenosine Diphosphate↗
PubMed1978

Lipoproteins and the inhibitory effect of human endothelial cells on platelet function.

We investigated the effect of plasma low density lipoproteins (LDL), very low density lipoproteins (VLDL), and high density lipoproteins (HDL) on the platelet inhibitory effect of primary cultures of human endothelial cell monolayers (ECM). ECM incubated with lipoprotein-deficient plasma (LDP) for 2 hours at 37 degrees C had an inhibitory effect on ADP- and collagen-induced platelet aggregation and prostaglandin production in platelet-rich plasma similar to that observed when ECM were preincubated with growth medium or plasma. Concentrations of LDL in LDP up to protein concentration of 1600 microgram/ml had an inhibitory effect on the endothelial cells' ability to modulate these platelet reactions. VLDL at the highest concentration (1600 microgram/ml) had a slightly inhibitory effect, whereas HDL showed no such effect. The inhibitory effect of LDL was not observed during the first hour of incubation. When HDL in concentrations similar to or higher than LDL were combined with LDL, the inhibitory effect of LDL was partially reduced. VLDL combined with LDL or HDL did not interfere with the effects of the later fractions. The inhibitory effect of LDL was significantly reduced when LDL were diluted in whole plasma. Prostacyclin which is synthesized and released from the endothelial cells and contributes to the inhibitory effect upon platelets did not change its effect on platelet reactivity by preincubation with the various lipoprotein fractions. The current studies may indicate that LDL have a direct effect on the endothelial cells and that this effect may be partially counteracted by HDL. This effect of LDL on the endothelial cells reduces the endothelium's ability to inhibit platelet aggregation and thus could favor the tendency to thrombus formation.

Blood Platelets↗
PubMed1978

Effect of aspirin on thrombin-induced adherence of platelets to cultured cells from the blood vessel wall.

An in vitro method was used to detect adherence of (51)Cr-labeled platelets to monolayers of cultured human endothelial, fibroblast, and smooth muscle cells. Washed platelets did not adhere to untreated or aspirin-treated endothelial monolayers in the absence of thrombin. In contrast, thrombin-induced platelet aggregates adhered to all of the monolayers but adherence to endothelium was significantly less than to the other cells. Additional evidence for adherence of platelets to the endothelium was provided by scanning and transmission electron microscopy. Thrombin-induced platelet adherence to endothelium was inhibited by hirudin. Platelet adherence induced by thrombin was enhanced significantly by treatment of the endothelial monolayer with 1-2 mM aspirin. This increase in adherence was seen even when aspirin-treated platelets were used; adherence values approached those seen with fibroblasts and smooth muscle cells. An aspirin concentration of 0.1 mM was sufficient to block thrombin-induced malonaldehyde production in platelets but it did not interfere with the inhibitory effect of the endothelium against platelet adherence. The effect of aspirin on the endothelium was temporary and inhibitory activity of the endothelium was restored 1 h after aspirin had been removed from the incubation system. The ability of thrombin to cause adherence of platelets to undamaged endothelium, and the potential for aspirin to enhance this adherence have implications for mechanisms which operate in platelet interaction with the blood vessel wall.

Aspirin↗
PubMed1978

Insulin receptors in human endothelial cells: identification and characterization.

Specific binding of 125I-insulin was found in cultured human endothelial cells obtained from human umbilical veins. The binding reaction was rapid and reversible, demonstrated receptor site-site interactions of the negatively cooperative type, and was dependent on the temperature, pH and duration of incubation. At 21 degrees C, steady-state conditions of binding occurred in 90 minutes, the pH optimum was 7.8 and less than 10% of the labeled hormone was degraded. Binding of tracer amounts of 125I-insulin was inhibited by concentrations of unlabeled insulin as low as 0.2 ng/ml and 50% inhibition was obtained at 2-5 ng/ml of unlabeled insulin. Unlabeled porcine insulin, porcine proinsulin and desoctapeptide insulin inhibited the binding of 125I-porcine insulin in direct proportion to their biological potencies, whereas to the cells was inhibited by antibodies against insulin receptors. We conclude that human endothelial cells possess specific receptors for insulin whose physio-chemical properties are similar to those of insulin receptors in other tissues.

Binding, Competitive↗
PubMed1978

Efficacy of graded-compression antiembolism stockings in patients undergoing total hip arthroplasty.

A prospective randomized trial evaluated graded-compression antiembolism stockings for prevention of leg vein thrombosis as assessed by Doppler ultrasound, in patients undergoing total hip replacement. The study was terminated after the evaluation of 18 patients revealed a significantly greater incidence of deep vein thrombosis, documented by phlebography, in patients without stockings (5 of 10) compared to those with stockings (none of 8, p less than 0.03). Three of the patients with thrombosis developed pulmonary emboli. Although the sample size of this study is small, the implication that graded-compression stockings reduce the incidence of leg vein thrombosis is strong and is supported by the results of other recent trials. These findings are at variance with earlier studies which failed to document efficacy of elastic stockings, which involved products which did not provide graded limb compression.

Aged↗