Biomedical subjects

C J Jen

Publications and source records attributed to C J Jen.

At least 37 records · Page 2Linked to original sources

PubMed1996

Regulation of plasminogen activator inhibitor activity by plasmin in endothelial cells.

The fibrinolytic activity in endothelial cells was regulated by balance of plasminogen activators and plasminogen activator inhibitors. Plasmin can specifically inhibit the biosynthesis of tissue-type plasminogen activator (t-PA), but not plasminogen activator inhibitor, type 1 (PAI-1) in endothelial cells. The PAI activity in the conditioned medium of endothelial cells was low and remained constant in 24 hours. However, the PAI activity in the conditioned medium of the plasmin-pretreated cells increased linearly in 24 hours. Pretreatment with protein kinase C inhibitors, H-7 or staurosporine, partially suppressed the PAI activity induced by plasmin. Pretreatment of endothelial cells with a G-protein inhibitor pertussis toxin resulted in an inhibition of the plasmin-induced PAI activity. The phospholipase A2 inhibitor mepacrine specifically eliminated the effect of plasmin stimulation on PAI activity. Cyclooxygenase and lipoxygenase inhibitors also partially inhibited the plasmin-stimulated PAI activity in endothelial cells. All these inhibitors did not affect the biosynthesis of the PAI-1 antigen in the presence or absence of plasmin. The results indicate that plasmin increased the PAI activity of endothelial cells via pathways in which protein kinase C, G protein, and phospholipase A2 may be involved.

1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine↗

PubMed1996

Flow-induced detachment of adherent platelets from fibrinogen-coated surface.

A study of the shear forces under which adherent platelets of different morphologies can be detached from surfaces was carried out using a newly designed tapered flow chamber, which covered the entire shear range of physiological circulation. Platelets that naturally settled on a fibrinogen-coated surface were exposed to shear flow and were subsequently processed for scanning electron microscopic observation. We found that 1) the density of platelets remaining after flow exposure decreased with local shear stress, 2) adherent platelets of different morphologies withstood different levels of shear stress: most round cells and 40% of the cells that had a few short pseudopods were detached at < 10 dyn/cm2, whereas most spread cells could withstand 50 dyn/cm2, 3) pulsatile flow was more effective in removing adherent platelets than equivalent steady flow, 4) cytochalasin D and colchicine retarded platelet shape change and made them more easily detached by shear forces, and 5) metabolic energy-depleted platelets spread readily and formed shear-resistant clumps. Our observations indicated that adherent platelets of different morphologies on a fibrinogen-coated surface could withstand different levels of flow shear stress.

Blood Circulation↗

PubMed1996

Platelet adhesion following the administration of tissue-type plasminogen activator and its reversal by vitamin E in rats.

Thrombolytic therapy is known to induce platelet-related side effects. We used a parallel-plate flow chamber, which was connected to the femoral artery of the rat, to measure platelet adhesion ex vivo. A collagen-coated arterioarterial shunt between two carotid arteries was used to measure shunt patency duration as an index of antithrombotic efficacy. Tissue-type plasminogen activator (t-PA), vitamin E, and the combination of these two were intravenously administered for 60 min. Measurements were performed before drug administration, and at 30, 60, 120 min after the initiation of drug infusion. Our results indicated that (1) treatments with t-PA or t-PA/vitamin E prolonged the time to shunt occlusion at 30 and 60 min; (2) t-PA enhanced platelet adhesion at 60 and 120 min; (3) vitamin E tended to reduce platelet adhesion; (4) t-PA/vitamin E reduced the t-PA-enhanced platelet adhesion; (5) at the high-density area of platelet adhesion under t-PA treatment, the adherent platelets demonstrated severe morphological changes which could be blocked by vitamin E. These data suggest that t-PA may enhance platelet adhesion in rats and that this adverse effect can be suppressed by co-administration of vitamin E.

Analysis of Variance↗

PubMed1995

Effects of exercise training and deconditioning on platelet function in men.

Platelets play an important role in the pathogenesis of cardiovascular disease. It has also been noticed that regular exercise can reduce the risk of cardiovascular disease. This is the first study to demonstrate that endurance exercise training may suppress platelet adhesiveness and aggregation and that deconditioning may reverse the training effects. Healthy male sedentary subjects were randomly divided into control and training groups. The trained men were trained on a bicycle ergometer at about 60% of maximal oxygen consumption for 30 minutes per day, 5 days per week for 8 weeks, then deconditioned for 12 weeks. During the experimental period, blood samples of the trained subjects were collected before and immediately after a progressive exercise test every 4 weeks. The same experiments were applied to the controls at the beginning of this study and 8 weeks thereafter. A tapered parallel-plate chamber was used to assess platelet adhesiveness. Platelet aggregation induced by ADP was evaluated by the percentage of reduction in single platelet count. Our results showed that (1) platelet adhesiveness and aggregability were increased by short-term strenuous exercise in both control and trained groups, but the enhancement of platelet aggregability was decreased after exercise training in the trained subjects; (2) at rest and immediately after strenuous exercise, platelet adhesiveness and aggregability were decreased by training, whereas they were unchanged in the control group; and (3) deconditioning reversed the training effects on resting and postexercise platelet adhesiveness and aggregability back to the pretraining state. These results suggest that platelet adhesiveness and aggregability may be depressed by exercise training but be reversed back to the pretraining state after deconditioning.

Blood Platelets↗

PubMed1995

Endogenous endothelium-derived relaxing factor inhibits platelet adhesion under whole blood flow conditions ex vivo.

In this study, we used carbachol to stimulate the endogenous endothelium-derived relaxing factor (EDRF) release in male Sprague-Dawley rats. One ml of native blood was drawn from the femoral artery and directly passed through a parallel-plate flow chamber. This system allowed us to examine ex vivo platelet adhesion to fibrinogen-coated surface under whole blood flow conditions. Our results demonstrated that 1) the intravenous administration of carbachol induced a transient decrease of blood pressure, reduction in platelet adhesion ex vivo, and elevation in platelet cGMP level; 2) coadministration of carbachol with hemoglobin, a scavenger of EDRF, inhibited these carbachol effects; 3) the administration of hemoglobin or N omega-nitro-L-arginine, an inhibitor blocking the NO synthesis pathway, caused elevated blood pressure in vivo, increased platelet adhesion ex vivo, and decreased cGMP content in platelets. We conclude that endogenous EDRF not only modulates vascular tone, but also influences platelet adhesion under flow conditions.

Animals↗

PubMed1994

Diacylglycerol formation induced by human plasmin in cultured endothelial cells.

Treatment of cultured bovine carotid artery endothelial cells with 10(-7) M plasmin increased the cellular diacylglycerol which was determined by the formation of [3H]palmitate-labeled diacylglycerol and diacylglycerol mass. Upon the stimulation with plasmin, a gradual increase in diacylglycerol formation was observed within 20 min then slightly declined. The maximal effect during the 1-h time course study was 45 and 55% increases in [3H]palmitate-labeled diacylglycerol and diacylglycerol mass, respectively, at 20 min after plasmin treatment. Formation of phosphatidylethanol was also studied in [3H]palmitate-prelabeled cells in the presence of ethanol. Treatment with plasmin for 20 min induced a significant 45% increase in phosphatidylethanol formation. The present results indicate that the plasmin-induced diacylglycerol formation in endothelial cells was at least in part mediated through the phospholipase D activation.

Animals↗

PubMed1994

Regional differences in prostaglandin production rates among porcine intrathoracic vessels.

To investigate the regional variability in intrathoracic vascular prostaglandin (PG) synthesis, we obtained vessel segments from porcine coronary artery (COA), thoracic aorta (AT), common carotid artery (CRA), pulmonary artery (PA), pulmonary vein (PV), and inferior vena cava (IVC). Vascular production rates of 6-keto-PGF1 alpha (an indicator for PGI2), PGF2 alpha, and PGE2 were measured both in unstimulated state and in arachidonic acid-stimulated state using immunosorbent assays. Our results indicated that PGI2 production rate in all vessel segments decayed with time after vessel dissection. In all vessel segments tested under unstimulated conditions, PGI2 production rates were about one order of magnitude higher than PGF2 alpha and PGE2 production rates of the same specimens. Results from unstimulated, 1.5 hr pre-incubated specimens indicated that i) PGI2 production rates in COA, AT, and PV were greater than those in CRA, PA, and IVC; ii) PGF2 alpha production rates from the same specimens were higher in PV than in AT, CRA, and IVC, while these in PA were higher than in IVC; and iii) PGE2 production rates from the same specimens were not significantly different from one another. Arachidonic acid added at about 1.5 hr after vessel harvest stimulated the PGI2 and PGF2 alpha synthesis rates by 3 to 15 folds. However, this arachidonic acid treatment caused 70 to 300-fold increases in PGE2 production rates, reaching levels comparable to PGI2. All three prostanoid production rates under stimulated conditions were also variable among different intrathoracic vessels. Although either physiological gas concentrations or local hemodynamic conditions alone can partially explain our results, which physiological parameter(s) actually causes these regional differences remains to be verified.

Animals↗

PubMed1994

Different effects of strenuous exercise and moderate exercise on platelet function in men.

BACKGROUND: Platelets play an important role in the pathogenesis of cardiovascular diseases. It is also noticed that on one hand, regular exercise can reduce the risk of cardiovascular diseases, and on the other hand, vigorous exercise provokes sudden cardiac death. We therefore hypothesize that various intensities of exercise may affect platelet function differently. METHODS AND RESULTS: Strenuous and moderate exercise (about 50% to 55% of peak oxygen consumption, VO2peak) on a bicycle ergometer in 10 sedentary and 10 physically active healthy young men was executed on two separate occasions. Blood samples were collected before and immediately after exercise. A newly designed tapered parallel plate chamber was used to assess platelet adhesiveness. Platelet aggregation induced by ADP was evaluated by the percentage of reduction in single platelet count. beta-Thromboglobulin (beta-TG) and platelet factor 4 (PF4) were measured by ELISA. In addition, a similar study on 5 patients with stable angina were also conducted. Our results showed that (1) in the sedentary healthy group, platelet adhesiveness and aggregation were increased by strenuous exercise and depressed by moderate exercise; (2) in the active healthy group, platelet adhesiveness and aggregation were enhanced by severe exercise, whereas only aggregation was decreased by moderate exercise; (3) in the patients with stable angina, platelet adhesiveness and aggregation were enhanced by strenuous exercise and adhesiveness was suppressed by moderate exercise; (4) the degree of hemoconcentration induced by acute exercise tended to be related to the severity of exercise in all subjects; and (5) although severe exercise elevated beta-TG and PF4, there were no significant changes in beta-TG, PF4, and the ratio of beta-TG to PF4 in healthy subjects after exercise. CONCLUSIONS: It is concluded that platelet adhesiveness and aggregability may be sensitized by strenuous exercise in both healthy subjects and patients with stable angina. In contrast, platelet function can be suppressed significantly by moderate exercise in the healthy and tends to be depressed in patients with stable angina. The former may increase the risk of cardiac arrest and the latter may protect us from cardiovascular diseases. In addition, the effects of acute exercise tend to be more pronounced in the sedentary than in the active.

Adult↗

PubMed1993

Effects of exercise training on the biosynthesis of prostacyclin and thromboxane in rats.

The effects of exercise training on eicosanoid levels were studied in male Wistar rats. One-month-old rats were trained on a drum exerciser at an intensity of around 70% of maximal oxygen consumption for 10 weeks (60 min day-1, 5 days week-1) after familiarization. Some animals of the same age did not exercise and served as a control. Two days after training, several blood vessels, including thoracic aortae, inferior vena cavae, external iliac arteries, external iliac veins, common carotid arteries and jugular veins, were excised and incubated for 10 min. Basal release of prostacyclin from these vessels was determined using [125I]radio-immunoassay (RIA) of 6-keto-PGF1 alpha. The levels of plasma prostacyclin and urinary metabolites of prostacyclin and thromboxane were also determined by RIA. Our results showed that trained animals had lower body weight and urine 11-dehydro-thromboxane B2 levels than the controls (P < 0.001 and P < 0.05, respectively). In contrast, urinary 2,3-dinor-6-keto-PGF1 alpha level was elevated after training (P < 0.05). Nonetheless, prostacyclin levels in plasma and from various dissected vessel segments, except thoracic aorta, did not change significantly after training. These findings suggest that exercise training may affect endogenous eicosanoid levels by increasing the basal release of prostacyclin and reducing the basal thromboxane level.

6-Ketoprostaglandin F1 alpha↗

PubMed1993

Human plasmin induces a receptor-mediated arachidonate release coupled with G proteins in endothelial cells.

Treatment of cultured bovine carotid artery endothelial cells with 10(-7) M plasmin increased arachidonate release coupled with the increase in prostacyclin production. The stimulatory effect of plasmin on arachidonate release could be divided into the early and late phases according to its calcium dependency and pertussis toxin sensitivity. The early phase of plasmin-induced arachidonate release was a calcium-dependent and pertussis toxin-sensitive response, which was observed within 20 min after plasmin treatment. The late phase was a calcium-independent and pertussis toxin-insensitive response, which was induced gradually from 20 to 60 min. Induction of the early phase of plasmin's effect required both the lysine binding and catalytic sites in plasmin molecule because it was inhibited either by the binding antagonist tranexamic acid or by the serine protease inhibitor aprotinin. Guanosine 5'-O-(2-thiotriphosphate) potentiated the effect of plasmin in permeabilized or nonpermeabilized cells, indicating that the early phase effect was mediated by a pertussis toxin-sensitive guanosine 5'-triphosphate (GTP)-binding protein. The late phase of plasmin's effect was due to the catalytic activity because it was inhibited by aprotinin but not by tranexamic acid. Microplasmin structurally having the catalytic sites induced a similar late phase effect. Plasmin did not elicit the metabolism of phosphatidyl polyphosphoinositides. These studies demonstrate that the activation of phospholipase A2, which results in arachidonate release, in the early phase of plasmin's effect is a receptor-mediation via GTP-binding protein that is not coupled through phospholipase C activation.

Animals↗

PubMed1992

Plasmin and the regulation of tissue-type plasminogen activator biosynthesis in human endothelial cells.

Plasmin inhibited the biosynthesis of tissue-type plasminogen activator (tPA) antigen by human umbilical vein endothelial cells (HUVEC) in a dose-dependent manner. The amount of tPA antigen found in the 24-h conditioned medium of cells treated with 100 nM plasmin for 1 h was 20-30% of that in the control group. However, in contrast to tPA, such treatment led to a 3-fold increase in plasminogen activator inhibitor (PAI) activity, whereas the amount of PAI type 1 antigen was unchanged. The effects of plasmin on HUVEC were binding- and catalytic activity-dependent and were specifically blocked by epsilon-aminocaproic acid. Microplasmin, which has no kringle domains, was less effective in reducing tPA antigen biosynthesis or enhancing PAI activity in HUVEC. Kringle domains of plasmin affected neither tPA antigen nor PAI activity of the cells. Other proteases including chymotrypsin, trypsin, and collagenase at comparable concentrations did not have a significant effect on the biosynthesis of tPA antigen or PAI activity of HUVEC. Thrombin stimulated the biosynthesis of tPA and PAI-1 antigens by HUVEC. Thrombin also stimulated an increase in the protein kinase activity in HUVEC, whereas plasmin inhibited the protein kinase activity of the cells. It is possible that plasmin regulates the biosynthesis of tPA in HUVEC through the signal transduction pathway involving protein kinase.

Aminocaproic Acid↗

PubMed1992

Cytoprotective effect of reduced glutathione in hydrogen peroxide-induced endothelial cell injury.

The kinetic effects of hydrogen peroxide (H2O2) on cultured endothelial cells isolated from bovine carotid artery were studied. The cytoprotective effects of glutathione (GSH) on H2O2-induced cell injury were also investigated. H2O2-induced a dose- and time-dependent cell injury in cultured endothelial cells. H2O2-induced cell injury was blocked by simultaneous treatment by catalase, but not by superoxide dismutase. H2O2 also induced endogenous PGI2 biosynthesis, and the maximum PGI2 production was reached after 1 h treatment. Stimulation of PGI2 production was parallel with arachidonate release from H2O2-treated cells. However the prostaglandin biosynthesis enzyme activity in cells was inhibited by H2O2 treatment. When the cells were treated with GSH, the intracellular GSH reached a plateau after 3 h treatment. Both H2O2-induced cell injury and PGI2 production were significantly inhibited by the 3 h pretreatment with GSH. The cytoprotective effect of GSH was completely inhibited by buthionine sulfoximine which is a specific inhibitor of gamma-glutamylcysteine synthetase. The results indicate that the cytoprotective effect of GSH on H2O2-induced cell injury in cultured bovine carotid artery endothelial cells depends on the increase in intracellular GSH content.

Animals↗

PubMed1992

A PC-based imaging system for automated platelet identification.

In this communication, a PC-based imaging system was developed for automatically identifying fluorescence-labeled individual platelets adherent to protein-coated surface under flow conditions. It is to eliminate the laborious and time-consuming task, and the subjective error of manual measurements. Based upon the features of adherent platelets, three passes of the image processing were developed for platelet identification. From the results, 90-95% accuracy could be routinely obtained. The platelet distribution and other related parameters could be easily extracted and investigated.

Algorithms↗

PubMed1992

Effects of acute exercise on the biosynthesis of eicosanoids in rats.

We conducted this study to evaluate the effects of different intensities of acute exercise on the regulation of endogenous eicosanoid levels in male Wistar rats. The animals were divided into 4 groups; i.e.: control, mild exercise, moderate exercise and severe exercise. Immediately after exercise, animals were sacrificed. Plasma prostacyclin (PGI2) level and PGI2 release from two vessel segments (i.e., thoracic aorta and inferior vena cava) were determined by a specific 6-keto-PGF1 alpha (125I) radioimmunoassay. Urine thromboxane was determined by a specific 11-dehydro-TXB2 (125I) radioimmunoassay and normalized by urine creatinine. Although both plasma PGI2 and urine thromboxane tended to be elevated by severe exercise, only the increase in thromboxane was statistically significant (p < 0.05). In addition, PGI2 release from both vessels were not affected by different intensities of acute exercise. We also observed that aortic PGI2 release was greater than their corresponding veins in each group. We therefore conclude that only severe acute exercise, rather than mild or moderate exercise, may affect prostacyclin-thromboxane balance in rats.

Animals↗

PubMed1991

Direct observation of platelet adhesion to fibrinogen- and fibrin-coated surfaces.

A flow system consisting of a parallel-plate flow chamber mounted on the epifluorescence video microscope was constructed to allow direct visualization of the entire platelet adhesion process under flow conditions. Digital image-processing techniques were applied to analyze the fluorescence images from video tapes. In this study we used cover glasses coated with either fibrinogen or fibrin as the testing surface of our flow chamber to compare platelet adhesion to both types of surfaces. We found that 1) platelets adhered to both types of protein-coated surfaces but not to uncoated glass; 2) platelets that adhered to fibrinogen were nonoverlapping, clustering, and saturated at approximately 40 cells/1,000 microns 2 at 445 s-1 surface shear rate and at approximately 60 cells/1,000 microns 2 at 70 s-1 surface shear rate; 3) platelets that adhered to fibrin were nonoverlapping, random, and saturated at approximately 55 cells/1,000 microns 2 at 445 s-1 surface shear rate and at approximately 65 cells/1,000 microns 2 at 70 s-1 surface shear rate; 4) ethyleneglycol- bis(beta-aminoethylether)-N,N'-tetraacetic acid, the snake venom halysin (against glycoprotein IIb-IIIa complex), and monoclonal antibody Ab-15 (against glycoprotein IIIa) blocked platelet adhesion to both surfaces; 5) Arg-Gly-Asp-Ser and monoclonal antibody LIBS-1 (against glycoprotein IIIa) partially inhibited platelet adhesion to fibrinogen-coated surface but were almost ineffective in preventing platelet adhesion to fibrin-coated surface; and 6) monoclonal antibody Ab-144 (against glycoprotein Ib) was ineffective for platelet adhesion on both surfaces. These observations provide basic characteristics of platelet adhesion to fibrinogen- and fibrin-coated surfaces under controlled flow conditions.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acid Sequence↗

PubMed1990

Platelet-fibrin interaction in the suspension and under flow conditions.

Interactions between platelets and fibrin are important in hemostasis but often confused with platelet-fibrinogen interactions. A stirred mixture of solubilized fibrin and washed platelets at neutral pH range showed drastic reduction in turbidity and concomitant platelet adhesion onto newly formed fibrin strands. This platelet-fibrin interaction did not require platelet activation nor did it cause platelet aggregation. A device consisting of a parallel-plate flow chamber mounted on a fluorescence microscope has been constructed to allow direct visualization and recording of platelet-fibrin interaction under flow conditions. Platelets in whole blood adhered to the fibrin-coated portion but not to the uncoated portion of the flow chamber. Slow motion playback of video tapes indicated that the adhesion phenomenon was a dynamic process that involved attaching, detaching, relocation and transient contact. The fibrin coating influenced platelet adhesion both by increasing the number of cells making short-term attachments to the surface and by increasing the duration of cells attached to the surface. These observations provided basic characteristics of platelet-fibrin interaction.

Blood Platelets↗

PubMed1989

Effects of acute exercise on bleeding time, bleeding amount and blood cell counts: a comparative study.

Twenty-five men and 26 women were studied to investigate the effects of acute strenuous exercise on hemostasis after obtaining their informed consent. After familiarization, they performed exercise on a bicycle ergometer at 75% of their predetermined maximal workload until exhaustion. Bleeding time, measured by the Simplate method, and venous blood cell counts of platelets (Plt), erythrocytes (RBC), leukocytes (WBC) were determined at rest and immediately after exercise. We found that bleeding time of Chinese in our study was longer than those of the westerners in other studies and that bleeding time was significantly shortened after exercise from 8.3 +/- .7 to 6.5 +/- .5 min in men and from 11.4 +/- .9 to 8.6 +/- .8 min in women (p less than 0.001). In men, but not in women, acute exercise also augmented the initial bleeding rate and bleeding amount from standard incisions. We also observed that RBC, WBC and Plt counts were greatly increased. The increased percentages for RBC, WBC and Plt in men were 7 +/- 1%, 59 +/- 7%, 16 +/- 3%, and those in women were 5 +/- 1%, 42 +/- 6% and 17 +/- 2% respectively.

Adult↗

PubMed1989

Turnover of platelets adhered to fibrinogen-coated surfaces.

The dynamic interactions between platelets and fibrinogen-coated surfaces were investigated by using a tube-flow device and a rotating rod device. The net platelet accumulation to the fibrinogen-coated surfaces in both devices reached maximal values of 30-40 platelets/1000 um2. This adhesion phenomenon was completely inhibited by EDTA. In the tube-flow device, the density of platelets adhered to the tube surface increased with flow time and decreased with distance from the tube inlet. These adhered platelets were difficult to be washed off the tube surface and showed little turnover. The platelet accumulation kinetics in a rotating rod device increased with rotation speed from 300 rpm to 1200 rpm. At 1200 rpm, about half of these platelets adhered to the rod were exchangeable with platelets in the suspension whereas the rest of them were permanent. The detachment of platelets from the rod surface depended on the presence of erythrocytes and platelets in the suspension and it was facilitated by the presence of EDTA in the suspension. These observations suggest that the turnover of platelets adhered to fibrinogen-coated surfaces depends on experimental conditions.

Blood Platelets↗