Effect of endothelin-1 on some hemostatic parameters in normotensive rats

Some parameters of hemostasis and fibrinolysis were investigated in rats administered with endothelin-1 (ET-1). ET-1 (0.5, 1.0, 5.0 nmol/kg) dose-dependently shortened the bleeding time (BT). Concomitantly significant shortening of the clotting time (CT) was observed. ET-1 produced prolongation of the activated partial thromboplastin time (APTT), whereas prothrombin time (PT) remained unchanged. ET-1 did not influence in vitro platelet aggregation induced by ADP and collagen. The euglobulin clot lysis time (ECLT) was significantly shortened after ET-1 administration. Our results suggest that ET-1 modulates the process of hemostasis and fibrinolysis in the rat.     

Red-wine polyphenols and inhibition of platelet aggregation: possible mechanisms, and potential use in health promotion and disease prevention

Correction of uremic platelet serotonin (5-HT) storage pool deficiency is one of the very early hemostatic effects of erythropoietin (Epo) therapy. In this work, platelet 5-HT with relation to primary hemostasis was studied in 15 hemodialysis patients treated with Epo for 8 months. Moreover, effects of ketanserin, a blocker of platelet and vascular smooth muscle cell 5-HT2A receptors, in these patients were followed. The parameters studied were compared with relevant values in healthy controls and in hemodialysis patients not treated with Epo, and remeasured in the long-term Epo patients after a 14-day oral ketanserin trial. Platelet 5-HT content in the eighth month of Epo therapy was not different from the one in untreated patients. Ristocetin- and collagen-induced platelet aggregation were enhanced in comparison with both control groups, as opposed to unaltered response to ADP and arachidonic acid. Fibrinogen concentration was lower than in the untreated group. An inverse correlation between ADP-induced platelet aggregation and the skin bleeding time (r=-0.536, p<0.05) and a positive one between the former and platelet 5-HT (r=0.644, p<0.01) were found. Platelet count correlated positively with both platelet 5-HT (r=0.823, p<0.0002) and ADP-induced platelet aggregation (r=0.596, p<0.02). Ketanserin produced a decrease in ristocetin-induced platelet aggregation, fibrinogen, and prolongation of the bleeding time. The first two of the changes correlated positively with their pre-ketanserin values (r=0.923, p<0.00001 and r=0.839, p< 0.0001, respectively). Post-ketanserin, positive correlations between depressed ristocetin- and arachidonic acid-induced platelet aggregation (r=0.760, p<0.005), and between collagen- and corresponding values of arachidonic acid- (r=0.622, p<0.02), ADP-induced platelet aggregation (r=0.396, p<0.01), and platelet 5-HT (r=0.654, p<0.05) were found. Efficient hemostasis in hemodialysis patients on protracted Epo therapy is, in part, dependent on enhanced platelet aggregability. Correction of platelet 5-HT storage pool deficiency is not evident in this stage but 5-HT still influences complex mechanisms of primary hemostasis. Ketanserin is of anticoagulant value in these patients but its effects must be weighted against possible exacerbation of the anemia.     

The antiplatelet activity of ancrod on administration to rabbits

Ancrod, a thrombin-like enzyme purified from the venom of Calloselasma rhodostoma, was administered to rabbits intravenously, and blood samples were obtained at 1, 3, 6, 10, and 24 hours after infusion. Ancrod caused a rapid and sustained defibrinogenation within the first 6 hours, with production of fibrinogen degradation products (FDPs) peaking at 1 hour and declining to background level at 6 hours. No significant changes in platelet count, white cell count, or hematocrit was observed. Citrated PRP prepared 1, 3, and 6 hours after ancrod infusion showed diminished aggregation, adenosine triphosphate (ATP) release, and thromboxane B2 formation on the addition of collagen. Although platelet suspension prepared from defibrinogenated platelet-rich plasma (PRP) at 3 hours showed no significant change in aggregation and ATP-releasing activity, the latent period of platelet aggregation was prolonged. When the remaining platelet-poor plasma obtained from defibrinogenated PRP at 3 hours was used to suspend the normal washed platelets prepared from PRP before ancrod infusion, the platelets showed a similar defect in aggregation and release action. Addition of fibrinogen (200 micrograms/ml to 2 mg/ml) to the above preparation partially restored aggregation but not capacity for secretion and thromboxane formation. When normal washed platelets were suspended with the defibrinogenated plasma, prepared by mixing ancrod with normal plasma in vitro and removing the formed fibrin, the platelet suspension showed impaired platelet aggregability, and the aggregability could be restored to the normal level by the addition of exogenous fibrinogen to this preparation.(ABSTRACT TRUNCATED AT 250 WORDS)     

Glucocorticoid regulation of adrenomedullin in a rat model of endotoxic shock

Wistar rats were injected intravenously with bacterial lipopolysaccharide (LPS) and developed endotoxic shock with severe hypotension. This was accompanied by significantly elevated concentrations of adrenomedullin (AM) in the plasma and expression of high levels of AM mRNA in the lung. Pretreatment of the rats with dexamethasone (DEX) prevented hypotension caused by LPS administration, but plasma AM concentrations and AM mRNA levels in the lung remained elevated. Adrenalectomized (ADX) rats developed a more severe form of circulatory shock in response to a low-dose of LPS. This was accompanied by only a slight increase in circulating AM in the plasma. However, pretreatment of ADX rats with DEX caused substantial elevations of plasma AM concentrations and expression of AM mRNA in the lung. Our studies demonstrate that glucocorticoid upregulates the expression and secretion of AM in vivo, and endogenous glucocorticoid is required for increased AM secretion under certain conditions such as endotoxic shock.     

Delayed closed reduction of rotatory atlantoaxial dislocation: case report and literature review

The effect of inhaled nitric oxide (iNO) on bleeding time and platelet aggregation was studied in nine newborn infants with resolving pulmonary hypertension. Infants treated with iNO at 40 ppm for 30 minutes had bleeding times that were nearly twofold longer than those obtained 24 hours after iNO was discontinued. iNO had no effect on in vitro platelet aggregation studies.     

Tetrafibricin: a nonpeptidic fibrinogen receptor inhibitor from Streptomyces neyagawaensis. (II). Its antiplatelet activities

Tetrafibricin; a nonpeptidic fibrinogen inhibitor from microbial origin, showed potent antiaggregation activities on human platelet aggregation induced by either ADP, thrombin or collagen (IC50s = 5.6, 7.6 and 11 microM, respectively) in platelet rich plasma. The ability to inhibit aggregation in platelets treated with chymotrypsin confirmed the GPIIb/IIIa blockage of tetrafibricin. Tetrafibricin blocked the release of serotonin induced by ADP but it did not block the release reaction induced by thrombin. When added to platelets formerly aggregated with ADP, tetrafibricin caused rapid and complete deaggregation. As for the selectivity among other Arg-Gly-Asp -dependent integrins, tetrafibricin seems to be more specific for glycoprotein (GP) IIb/IIIa than RGDS is. This is because it had no effect on adhesion of bovine aortic endothelial cells to RGD-containing proteins. Tetrafibricin is the first nonpeptidic fibrinogen receptor inhibitor that may be valuable for the study on platelet aggregation inhibitors.     

Inhaled nitric oxide inhibits human platelet aggregation, P-selectin expression, and fibrinogen binding in vitro and in vivo

BACKGROUND: Recent data suggest that inhaled NO can inhibit platelet aggregation. This study investigates whether inhaled NO affects the expression level and avidity of platelet membrane receptors that mediate platelet adhesion and aggregation. METHODS AND RESULTS: In 30 healthy volunteers, platelet-rich plasma was incubated with an air/5% CO2 mixture containing 0, 100, 450, and 884 ppm inhaled NO. ADP- and collagen-induced platelet aggregation, the membrane expression of P-selectin, and the binding of fibrinogen to the platelet glycoprotein (GP) IIb/IIIa receptor were determined before (t0) and during the 240 minutes of incubation. In addition, eight patients suffering from severe adult respiratory distress syndrome (ARDS) were investigated before and 120 minutes after the beginning of administration of 10 ppm inhaled NO. In vitro, NO led to a dose-dependent inhibition of both ADP-induced (3+/-3% at 884 ppm versus 70+/-6% at 0 ppm after 240 minutes; P<.001) and collagen-induced (13+/-5% versus 62+/-5%; P<.01) platelet aggregation. Furthermore, P-selectin expression (36+/-7% of t0 value; P<.01) and fibrinogen binding (33+/-11%; P<.01) were inhibited. In patients with ARDS, after two who did not respond to NO inhalation with an improvement in oxygenation had been excluded, an increase in plasma cGMP, prolongation of in vitro bleeding time, and inhibition of platelet aggregation and P-selectin expression were observed, and fibrinogen binding was also inhibited (19+/-7% versus 30+/-8%; P<.05). CONCLUSIONS: NO-dependent inhibition of platelet aggregation may be caused by a decrease in fibrinogen binding to the platelet GP IIb/IIIa receptor.     

Adhesive ligand binding to integrin alpha IIb beta 3 stimulates tyrosine phosphorylation of novel protein substrates before phosphorylation of pp125FAK

Tyrosine phosphorylation of multiple platelet proteins is stimulated by thrombin and other agonists that cause platelet aggregation and secretion. The phosphorylation of a subset of these proteins, including a protein tyrosine kinase, pp125FAK, is dependent on the platelet aggregation that follows fibrinogen binding to integrin alpha IIb beta 3. In this report, we examined whether fibrinogen binding, per se, triggers a process of tyrosine phosphorylation in the absence of exogenous agonists. Binding of soluble fibrinogen was induced with Fab fragments of an anti-beta 3 antibody (anti-LIBS6) that directly exposes the fibrinogen binding site in alpha IIb beta3. Proteins of 50-68 KD and 140 kD became phosphorylated on tyrosine residues in a fibrinogen-dependent manner. This response did not require prostaglandin synthesis, an increase in cytosolic free calcium, platelet aggregation or granule secretion, nor was it associated with tyrosine phosphorylation of pp125FAK. Tyrosine phosphorylation of the 50-68-kD and 140-kD proteins was also observed when (a) fibrinogen binding was stimulated by agonists such as epinephrine, ADP, or thrombin instead of by anti-LIBS6; (b) fragment X, a dimeric plasmin-derived fragment of fibrinogen was used instead of fibrinogen; or (c) alpha IIb beta 3 complexes were cross-linked by antibodies, even in the absence of fibrinogen. In contrast, no tyrosine phosphorylation was observed when the ligand consisted of monomeric cell recognition peptides derived from fibrinogen (RGDS or gamma 400-411). Fibrinogen-dependent tyrosine phosphorylation was inhibited by cytochalasin D. These studies demonstrate that fibrinogen binding to alpha IIb beta 3 initiates a process of tyrosine phosphorylation that precedes platelet aggregation and the phosphorylation of pp125FAK. This reaction may depend on the oligomerization of integrin receptors and on the state of actin polymerization, organizational processes that may juxtapose tyrosine kinases with their substrates.     

SC-49992--a potent and specific inhibitor of platelet aggregation

Fibrinogen binding is required for platelet aggregation and subsequent thrombus formation. SC-49992 (SC), an RGDF mimetic, is a potent and specific inhibitor of the binding of fibrinogen to its receptor on activated platelets, glycoprotein IIb/IIIa (IC50 0.7 microM). SC was more potent (1-5 microM) than either RGDS, RGDF or the gamma chain dodecapeptide in blocking platelet aggregation to a variety of agonists in both dog and human platelet rich plasma. SC was more potent as an inhibitor of GP IIb/IIIa on platelets than it was against other integrin and non-integrin receptors, including the RGD-dependent vitronectin receptor and other non-RGD-dependent integrins such as CDII/CD18. SC had little effect on ristocetin induced agglutination. SC blocked ex vivo collagen induced aggregation in dogs and collagen induced thrombocytopenia in rats. These data suggest that elimination of the Arg-NH2 and the Arg-Gly amide bond of RGDF provided increased inhibitory potency and specificity. This structural modification may be of value in the development of other more potent RGDF mimetics for the inhibition of platelet aggregation.     

Effects of mental and physical stress on platelet function in patients with stable angina pectoris and healthy controls

The effects of mental and physical stress on platelet function in patients with stable angina pectoris and healthy controls were investigated. Platelet function was studied at rest, and during mental stress (colour word test), or after exercise (bicycle ergometry), in 113 angina patients (21 on aspirin) and 50 matched controls. Platelet function was assessed by filtragometry ex vivo (reflecting platelet aggregability), by measuring platelet secretion (beta-thromboglobulin and platelet factor 4 levels in plasma), and by Born aggregometry in vitro. At rest, platelet function did not differ between patients and controls. Exercise increased platelet aggregability and secretion similarly in both groups. Aspirin did not attenuate the platelet activating effect of exercise despite inhibition at rest. Mental stress increased heart rate, blood pressure and plasma catecholamines, but platelet responses were highly variable. However, mental stress tended to shorten filtragometry readings in patients but not in controls (P < 0.05 between the groups); plasma beta-thromboglobulin showed a similar difference between patients and controls (P < 0.05 between the groups; aspirin-treated patients included). Physical exercise activates platelets in patients with stable angina pectoris and healthy controls. Aspirin is not an effective inhibitor of exercise-induced platelet aggregation. Platelet responses to mental stress are variable, but more pronounced in angina patients.     

Effect of inhibition of nitric oxide synthesis on the uptake of LDL and fibrinogen by arterial walls and other organs of the rat

1. The effects of administering 3 mg ml-1 NG-nitro-L-arginine methyl ester (L-NAME), an inhibitor of nitric oxide (NO), on the uptake of low density lipoprotein (LDL), fibrinogen and blood pressure were determined in conscious, unrestrained, cannulated normotensive and spontaneously hypertensive (SHR) Wistar rats. 2. The uptake of LDL and fibrinogen, labelled respectively with 125I or 131I via the adduct tyramine cellobiose ([125I]TC-LDL and [131I]TC-fibrinogen), were compared in aortic walls, heart, skeletal muscle, lung, liver, kidney and adrenal during the final 24 h of 6 days' administration of L-NAME in the drinking water. 3. In control normotensive rats, the systolic blood pressure did not change significantly over 6 days, while administration of L-NAME in normotensive rats increased the blood pressure progressively and significantly to about 170 mmHg over the same period. 4. In normotensive rats L-NAME increased significantly the uptake of both LDL and fibrinogen by aortic walls and heart, but not by muscle, lung, liver, kidney and adrenal. 5. The blood pressure in SHR was about 170 mmHg before administration of L-NAME and did not increase significantly after 6 days of treatment. In these rats the uptake of LDL or of fibrinogen was increased only in the heart but not in aortic walls nor in any of the other organs. 6. In normotensive rats the increase in blood pressure caused by inhibition of NO generation was associated with increases in the uptake of the atherogenic plasma proteins LDL and fibrinogen by the wall of the aorta and by the heart but not by the skeletal muscle, lung, liver, kidney and adrenal. The slightly higher blood pressure of SHR treated with L-NAME was not associated with increased uptake of LDL or fibrinogen by aorta nor by any organ except heart. Thus, while in normotensive rats the increase in blood pressure caused by inhibition of NO generation was associated with increase in the uptake of atherogenic plasma proteins LDL and fibrinogen by the wall of the aorta and by the heart, in SHR which showed uptakes similar to the normotensive animals, the non-significant increase in blood pressure induced by inhibition of NO generation was not associated with increased uptake of LDL or fibrinogen in any organ except the heart.7. These results are consistent with effects, demonstrated earlier, of infusing the pressor agents noradrenaline, adrenaline and angiotensin II, which produce increases in uptake of LDL and fibrinogen by aortic wall, whereas this is not so in spontaneously hypertensive rats.     

Priming of platelet alphaIIbbeta3 by oxidants is associated with tyrosine phosphorylation of beta3

Reactive oxygen species play an important role at the site of vascular injuries and arterial thromboses. We studied the mechanism mediating platelet aggregation induced by H2O2, a major cellular oxidant. Exposure to H2O2 triggered platelet aggregation, but only when the platelets were stirred. Strong platelet aggregation induced99032416 required the presence of the tyrosine phosphatase inhibitor sodium orthovanadate (NaVO4) and was dependent on the participation of integrin alphaIIbbeta3 (glycoprotein IIb-IIIa). A specific inhibitor of alphaIIbbeta3 blocked platelet aggregation induced by H2O2 and NaVO4, thus confirming that aggregation requires this receptor. In the presence of H2O2 and NaVO4, multiple platelet substrates were phosphorylated on tyrosine. Such tyrosine kinase response was necessary but not sufficient to activate alphaIIbbeta3, as detected by binding of soluble fibrinogen to platelets. Stirring of the platelets exposed to H2O2 and NaVO4 was also needed to allow for binding of fibrinogen to alphaIIbbeta3. The tyrosine kinase inhibitor genistein was able to block platelet aggregation induced by H2O2 and NaVO4, thus confirming that tyrosine kinase activity was needed to trigger alphaIIbbeta3 activation on stirring. N-Acetyl-L-cysteine, a cell-permeant antioxidant, blocked the tyrosine phosphorylation of platelet substrates and also the platelet aggregation induced by H2O2 and NaVO4. We found that beta3 was phosphorylated on tyrosine in platelets exposed to H2O2 and NaVO4, even in the absence of aggregation. Hence, tyrosine phosphorylation of beta3 might contribute to the "priming" of alphaIIbbeta3 induced by H2O2 and NaVO4, whereby the receptor can become activated on stirring of the platelets.     

Anesthesia with sodium pentobarbital enhances lipopolysaccharide-induced cardiovascular dysfunction in rats

Lipopolysaccharide (LPS)-induced hypotension and impaired aortic contraction to norepinephrine (NE) are thought to be consequent to induction of nitric oxide synthase (iNOS). Anesthesia is often employed in studies of the mechanisms mediating LPS-induced cardiovascular dysfunction in rats. Since sympathetic nervous system activity and compensatory mechanisms can be altered by anesthesia, this study was designed to determine a) if the cardiovascular dysfunction associated with LPS (5 mg/kg, i.v.)-induced endotoxin shock is enhanced in anesthetized compared with conscious male Wistar rats, and b) the potential role of iNOS in these responses to LPS. Arterial pressure and heart rate were continuously measured via a femoral arterial cannula. Six hours after LPS, conscious rats had a stable mean arterial pressure (MAP) and were tachycardic, while anesthetized rats showed a significant decrease in MAP without tachycardia. Small mesenteric arterioles (200-300 microns) were isolated, and the endothelium was removed six h after LPS. Intraluminal diameter was continuously recorded while vessels were maintained at a constant intraluminal pressure of 40 mmHg. Norepinephrine-induced contraction and oscillations/min were impaired to a greater extent in arterioles from LPS-treated anesthetized rats than in those from conscious rats. Calcium-dependent and -independent nitric oxide formation, reflected as cGMP accumulation, were also determined in aortic rings treated with a chelator of Ca2+, EGTA, or the inhibitor of nitric oxide synthase activity, L-NAME. In rings from saline-treated conscious and anesthetized rats, cGMP accumulation was significantly reduced by EGTA and L-NAME, indicating calcium-dependent constitutive (cNOS) activity. However, in aortic rings from LPS-treated conscious and anesthetized rats, cGMP accumulation was not affected by EGTA and was significantly greater in rings from anesthetized vs. conscious rats. These results suggest that cardiovascular dysfunction is more prominent in LPS-treated anesthetized vs. conscious rats. This effect may be related to increased induction of iNOS in the presence of anesthesia.     

Losartan inhibits experimental venous thrombosis in spontaneously hypertensive rats

The potential antithrombotic action of losartan, the AT1 receptor antagonist, in an experimental model of venous thrombosis in spontaneously hypertensive rats (SHR) and Wistar Kyoto rats (WKY) was tested. The involvement of nitric oxide and prostacyclin in this effect was also studied. Venous stasis was induced by ligation of the vena cava. Losartan, after administration of a single, hypotensive dose (10 mg/kg, p.o.), significantly reduced the thrombus weight in SHR but not in WKY. The antithrombotic activity of losartan in SHR was abolished by NG-nitro L-arginine methyl ester (L-NAME) (30 mg/kg s.c.) but not by indomethacin (2.5 mg/kg s.c.). No changes in primary hemostasis, platelet aggregation, coagulation parameters such as activated partial thromboplastin time, prothrombin time, euglobulin clot lysis time, and fibrinogen level, either in SHR or in WKY rats, were found. Our results indicate the NO-dependent mechanism in the antithrombotic effect of losartan on venous thrombosis in SHR.     

Protection of platelet glycoprotein IIb/IIIa receptor complex preserves platelet function during in vitro ventricular assisted circulation

Platelet dysfunction probably contributes to bleeding associated with ventricular assist devices (VADs). Previous evidence suggests that VAD associated platelet dysfunction may be due to dysfunction of the platelet fibrinogen receptor. The purpose of this investigation was to test the hypothesis that selective protection of platelet fibrinogen receptor preserves platelet aggregating ability during in vitro ventricular assisted circulation. Eight in vitro nonpulsatile centrifugal VAD circuits were simulated for four days using 450 ml of fresh human whole blood. Temperature, activated clotting time, pH, PCO2, PO2, Ca2+, and glucose were maintained at physiologic values. Flow was maintained at a constant 2.0 L/min/m2. We examined whole blood platelet aggregation induced by ristocetin, collagen, and adenosine diphosphate (ADP). We added a highly specific reversible inhibitor (MK-383) of the glycoprotein (GP) IIb/IIIa receptor complex before start of circulation to the final four VAD experiments. ADP induced aggregation decreased within the first hour of circulation. Ristocetin and collagen induced aggregation decreased to negligible levels after 10 hours of circulation. With MK-383, ristocetin induced aggregation was preserved. Addition of MK-383 did not alter the decrease of ADP and collagen induced aggregation. These results suggest platelet aggregating ability is maintained with protection of the platelet fibrinogen receptor during in vitro ventricular assisted circulation.     

Specific interaction of HLA antibodies (eluates) with washed platelets

The mechanism of complement-independent action of HLA-A2 antibodies (eluates) on washed platelets was investigated. HLA-specific alteration was confirmed by serological (platelet micro-complement fixation), morphological (platelet spreading) and functional parameters (platelet aggregation, inhibition of collagen-induced platelet aggregation, [14C]serotonin release). In the presence of fibrinogen and calcium ions, HLA antibodies induced instantaneous platelet aggregation and release. Although no morphological (spreading) and functional changes (collagen-induded aggregation) were seen, these platelets did not aggregate or release when fibrinogen was subsequently added. When platelets--in the presence of fibrinogen--were incubated with antibody concentrations too low to induce platelet aggregation or release, specific reduction of platelet reactivity was observed by subsequent collagen aggregation. HLA-specific action of antibodies on washed platelets was inhibited by apyrase and acetyl-salicylic acid, indicating an active participation of platelets in HLA antibody-induced platelet alteration.     

Effect of intensified red blood cell aggregability on arterial pressure and mesenteric microcirculation

Intensified aggregability of red blood cells (RBC) was produced in adult white rats by the step-by-step intravascular administration of a high-molecular-weight dextran, with a molecular weight approximating that of blood fibrinogen. As a result, the systemic arterial pressure was elevated by more than one-third of the initial level, whereas the diameter of arterioles in the intestinal mesentery remained practically unchanged. This provided sufficient grounds for the conclusion that the increase in the total peripheral resistance was due to disturbances in blood rheological properties. Despite the elevated arterial pressure, the blood flow velocity in mesenteric arterioles displayed a clear-cut tendency to slow down. Simultaneously, a large number of RBC aggregates appeared in the mesenteric microvessels. In patients with a stable form of arterial hypertension the RBC aggregability index was found to be significantly increased as compared with that of the healthy control group. Following treatment with Ca(2+)- and beta-adrenergic blockers the index decreased significantly in parallel with the lowering of arterial pressure. The obtained results suggest that the intensified RBC aggregation in microvessels causing a disturbance of normal blood flow structure, and hence of blood rheological properties, might be an important factor responsible for the elevation of systemic arterial pressure in humans with arterial hypertension.     

Primary fibrinolysis during supraceliac aortic clamping

PURPOSE: An increased incidence of bleeding complications has been observed after supraceliac aortic clamping (SCC). This study was performed to identify possible hemostatic abnormalities that contribute to this problem. METHODS: A prospective cohort study over a 3-month period was performed by comparing hemostatic parameters in 10 consecutive patients who required elective SCC with those of eight concurrent randomly selected control subjects who required infrarenal clamping (IRC) for abdominal aortic reconstruction. Measures of coagulation, fibrinolysis, platelet function, temperature, hemodilution, and hepatic function were performed at selected times before, during, and after operation. RESULTS: Aneurysm size, fibrinogen, D-dimers, prothrombin, partial thromboplastin time, platelet counts, bleeding times, hemodilution, and temperature were comparable in both groups. Patients in the SCC group, however, consistently developed a primary fibrinolytic state within 20 minutes after supraceliac clamping, reflected by significantly decreased euglobulin clot lysis times (ECLT; p < 0.0001), elevated tissue plasminogen activator (t-PA) levels (p < 0.0006), elevated t-PA-to-plasminogen activator inhibitor-1 ratios (p < 0.0001), and reduced alpha 2-antiplasmin levels (p < 0.002). SCC produced hepatocellular injury documented by elevations in both aspartate transaminase (p < 0.0001) and lactate dehydrogenase (p < 0.009). CONCLUSIONS: SCC rapidly induces a primary fibrinolytic state manifested by increased circulating t-PA, reduced alpha 2-antiplasmin, and increased fibrinolytic activator-to-inhibitor ratios. These effects may be a result of hepatic hypoperfusion caused by SCC leading to insufficient clearance of t-PA. Antifibrinolytic agents may be of benefit if bleeding develops after aortic procedures that require supraceliac clamping.     

The changes of blood gas analysis values and platelet aggregability on acute phase in the experimental model of pulmonary embolism prepared by sephadex G-75 (SG-75) injection

To study pathophysiologic phenomena in acute pulmonary embolism, we injected sephadex G-75 (SG-75) into rabbit auricular veins and measured the changes in blood gases and in platelet aggregability. Severe hypoxemia developed within 10 minutes of SG-75 injection. Microscopic examination of samples taken 120 minutes after SG-75 injection pulmonary artery had been embolized by the SG-75 particles, and that thrombin had formed around the particles. The lowest platelet counts were measured 10 minutes after SG-75 injection. The rates of platelet aggregation induced by adenosine diphosphate and by platelet-activating factor were abnormally low until 40 minutes after SG-75 injection. These results suggest that platelets were activated by anoxia and that the activated platelets moved around the emboli after obstruction of the pulmonary artery. We conclude that decreases in PaO2 and changes in platelet aggregability exacerbate the pathophysiologic processes in acute pulmonary embolism.     

A new model of dual interacting ligand binding sites on integrin alphaIIbbeta3

The platelet integrin alphaIIbbeta3 mediates platelet aggregation and platelet adhesion. This integrin is the key to hemostasis and also to pathologic vascular occlusion. A key domain on alphaIIbbeta3 is the ligand binding site, which can bind to plasma fibrinogen and to a number of Arg-Gly-Asp (RGD)-type ligands. However, the nature and function of the ligand binding pocket on alphaIIbbeta3 remains controversial. Some studies suggest the presence of two ligand binding pockets, whereas other reports indicate a single binding pocket. Here we use surface plasmon resonance to show that alphaIIbbeta3 contains two distinct ligand binding pockets. One site binds to fibrinogen, and a separate site binds to RGD-type ligands. More importantly, however, the two ligand binding pockets are interactive. RGD-type ligands are capable of binding to alphaIIbbeta3 even when it is already occupied by fibrinogen. Once bound, RGD-type ligands induce the dissociation of fibrinogen from alphaIIbbeta3. This allosteric cross-talk has important implications for anti-platelet therapy because it suggests a novel approach for the dissolution of existing platelet thrombi.