Preferences and illusions in quantified spatial relational reasoning

The following presents the results of an investigation of strategies and preferences in human reasoning about quantified spatial relational assertions. An empirical study revealed a clear preference effect for specific models: The initially constructed model depends on the number of mental model operations. The participants' strategies can be classified as follows: (1) Models with grouped elements are preferred; (2) Models are constructed according to a parsimonious representation strategy. Systematic reasoning errors and illusions can be identified with logical connectors (AND: 86 % valid initial models; XOR: 47 %; Wilcoxon z = 4.6; p < .001). Error rates were smallest when using two universal quantifiers (All-All), they increase significantly when using one (Some-All; All-Some) and again using none (Some-Some) (Page's L = 436; z = 3.40 p < .001). Although the different assertions allowed for multiple situations, the difficulty can be traced back to specific quantifiers and logical connectors.

Cross-Cultural Preferences in Spatial Reasoning

Abstract

How do people reason about spatial relations? Do people with different cultural backgrounds differ in how they reason about space? The aim of our cross-cultural study on spatial reasoning is to strengthen this link between spatial cognition and culture. We conducted two reasoning experiments, one in Germany and one in Mongolia. Topological relations, such as “A overlaps B” or “B lies within C”, were presented to the participants as premises and they had to find a conclusion that was consistent with the premises (“What is the relation between A and C?”). The problem description allowed multiple possible “conclusions”. Our results, however, indicate that the participants had strong preferences: They consistently preferred one of the possible conclusions and neglected other conclusions, although they were also logically consistent with the premises. The preferred and neglected conclusions were similar in Germany and Mongolia. We argue that the preferences are caused by universal cognitive principles that work the same way in the western culture and Mongolia.

Virologic and clinical outcomes of hepatitis B virus infection in HIV-HBV coinfected transplant recipients

Liver transplantation (LT) is the treatment of choice for end-stage liver disease, but is controversial in patients with human immunodeficiency virus (HIV) infection. Using a prospective cohort of HIV-hepatitis B virus (HBV) coinfected patients transplanted between 2001-2007; outcomes including survival and HBV clinical recurrence were determined. Twenty-two coinfected patients underwent LT; 45% had detectable HBV DNA pre-LT and 72% were receiving anti-HBV drugs with efficacy against lamivudine-resistant HBV. Post-LT, all patients received hepatitis B immune globulin (HBIG) plus nucleos(t)ide analogues and remained HBsAg negative without clinical evidence of HBV recurrence, with a median follow-up 3.5 years. Low-level HBV viremia (median 108 IU/mL, range 9-789) was intermittently detected in 7/13 but not associated with HBsAg detection or ALT elevation. Compared with 20 HBV monoinfected patients on similar HBV prophylaxis and median follow-up of 4.0 years, patient and graft survival were similar: 100% versus 85% in HBV mono- versus coinfected patients (p = 0.08, log rank test). LT is effective for HIV-HBV coinfected patients with complications of cirrhosis, including those who are HBV DNA positive at the time of LT. Combination HBIG and antivirals is effective as prophylaxis with no clinical evidence of HBV recurrence but low-level HBV DNA is detectable in approximately 50% of recipients.

Orthogonal coordinates and hyperquantization algorithm. The NH3 and H3O+ umbrella inversion levels

In order to describe the umbrella inversion mode, which is characteristic of AB(3)-type molecules, we have introduced an alternative hyperspherical coordinate set based on a parametrization of Radau-Smith orthogonal vectors and have considered constraints which allow us to enforce the C(3v) symmetry. Structural properties and electronic energies at equilibrium and barrier configurations have been obtained at MP2 and CCSD(T) levels of theory. Energy profiles have been calculated using the CCSD(T) method with an aug-cc-pVQZ basis set. The NH(3) and H(3)O(+) umbrella inversion levels are obtained by the hyperquantization algorithm for a one-dimensional calculation, using a specially defined hyperangle as the inversion coordinate. The results are compared with experimental and theoretical energy levels, in particular, with those obtained by calculations based on two-dimensional models. The emerging picture of the umbrella inversion based on this hyperangular coordinate compares favorably with respect to the usual valence-type description.

Immune tolerance therapy utilizing factor VIII/von Willebrand factor concentrate in haemophilia A patients with high titre factor VIII inhibitors

Factor VIII (FVIII) inhibitors remain a serious complication of treatment for patients with haemophilia A. Immune tolerance induction (ITI) can eliminate inhibitors in the majority of patients, but there are major concerns related with this therapy. Investigators have raised the possibility that the use of FVIII/von Willebrand factor (FVIII/VWF) concentrates may improve the success rate of ITI and may shorten the duration of therapy necessary to attain tolerance. This retrospective study describes 25 patients at five institutions in the USA, who were treated with FVIII/VWF concentrate as part of their ITI. These were all patients who were considered poor prognosis because of clinical and laboratory characteristics, which made ITI less likely to be successful or because of a poor response to initial ITI with a monoclonal/recombinant FVIII concentrate. Overall success (complete tolerization) was 32% with another 40% attaining partial tolerization, but not complete tolerization. Of those patients attaining only partial tolerization, two patients ultimately discontinued ITI and had return of their high titre inhibitors. Eight percent of patients failed to attain either partial or complete tolerization and discontinued ITI. Another 24% are continuing with ITI but have titres of >10 BU. This study adds further retrospective data to the information regarding the use of FVIII/VWF concentrate in ITI.

Thyroid-hormone effects on putative biochemical pathways involved in UCP3 activation in rat skeletal muscle mitochondria

In vitro, uncoupling protein 3 (UCP3)-mediated uncoupling requires cofactors [e.g., superoxides, coenzyme Q (CoQ) and fatty acids (FA)] or their derivatives, but it is not yet clear whether or how such activators interact with each other under given physiological or pathophysiological conditions. Since triiodothyronine (T3) stimulates lipid metabolism, UCP3 expression and mitochondrial uncoupling, we examined its effects on some biochemical pathways that may underlie UCP3-mediated uncoupling. T3-treated rats (Hyper) showed increased mitochondrial lipid-oxidation rates, increased expression and activity of enzymes involved in lipid handling and increased mitochondrial superoxide production and CoQ levels. Despite the higher mitochondrial superoxide production in Hyper, euthyroid and hyperthyroid mitochondria showed no differences in proton-conductance when FA were chelated by bovine serum albumin. However, mitochondria from Hyper showed a palmitoyl-carnitine-induced and GDP-inhibited increased proton-conductance in the presence of carboxyatractylate. We suggest that T3 stimulates the UCP3 activity in vivo by affecting the complex network of biochemical pathways underlying the UCP3 activation.

Long-lasting antithrombotic effects of a single dose of human recombinant, active site-blocked factor VII: insights into possible mechanism(s) of action

Tissue factor (TF) is important in initiating intravascular thrombosis. We demonstrated that active-site blocked factor VII (FVIIai) inhibits intravascular thrombosis for at least 6 h following a single injection, despite FVIIai plasma half-life was approximately 45 min. The aims of the present study were: (a) to determine the duration of the antithrombotic effects of a single injection of FVIIai; and (b) to assess whether FVIIai prolonged effects can be explained by a slow dissociation rate from TF in the arterial wall. Cyclic flow variations (CFVs), obtained in stenotic rabbit carotid arteries with endothelial injury, were abolished by either FVIIai (100 micro g kg-1 min-1 for 10 min) or hirudin (1 mg kg-1). After CFVs were abolished, carotid blood flow velocity was recorded continuously for 24 h. CFVs restored in all hirudin-treated animals after 2.1 +/- 0.3 h, while they restored in only four of nine FVIIai-treated rabbits in 10.1 +/- 2.2 h. Five animals in this group did not show restoration of CFVs up to 24 h. Immunohistochemistry revealed that FVIIai was still bound to the arterial wall 24 h following its administration, despite at this time FVIIai plasma levels were undetectable. Prothrombin time and partial thromboplastin time did not change significantly. FVIIai exerts potent, long-lasting antithrombotic effects without affecting systemic hemostatic parameters; a possible mechanism is a slow dissociation rate of FVIIai from TF. These proprieties make FVIIai particularly attractive as an antithrombotic intervention.

Expression of exogenous tissue factor pathway inhibitor in vivo suppresses thrombus formation in injured rabbit carotid arteries

OBJECTIVES

The aim of the present study was to test the hypothesis that retrovirus-mediated in vivo tissue factor pathway inhibitor (TFPI) gene transfer to the arterial wall would efficiently inhibit thrombosis without causing significant changes in systemic hemostatic variables.

BACKGROUND

Acute coronary syndromes (unstable angina and acute myocardial infarction) are usually caused by atherosclerotic plaque rupture, with consequent activation of the coagulation cascade and circulating platelets. Tissue factor (TF) exposure represents an early event in this pathophysiologic sequence, leading to activation of the extrinsic coagulation pathway and thrombin formation. Tissue factor pathway inhibitor is a naturally occurring inhibitor of the extrinsic pathway.

METHODS

In the present study, the gene coding for rabbit TFPI was inserted in a retroviral vector under control of a tetracycline-inducible promoter. Replication-defective, infectious, recombinant retroviruses were used to transfect rabbit carotid arteries with either TFPI or a reporter gene--green fluorescent protein (GFP).

RESULTS

Retroviral-mediated arterial gene transfer of TFPI resulted in potent inhibition of intravascular thrombus formation in stenotic and injured rabbit carotid arteries, whereas transfection of the contralateral carotid artery with GFP had no effect on thrombosis. No significant changes in systemic hemostatic variables (prothrombin time and partial thromboplastin time) were observed when thrombosis was inhibited.

CONCLUSIONS

These data suggest that retroviral-mediated transfection of the arterial wall with TFPI might represent an attractive approach for the treatment of thrombotic disorders.

Fatty acid chain elongation synthesis in eel (Anguilla anguilla) liver mitochondria

The properties of fatty acid chain elongation synthesis have been investigated in liver mitochondria of the European eel (Anguilla anguilla). The incorporation of [1-(14)C]acetyl-CoA into fatty acids shows a specific activity of 0.43+/-0.05 nmol/min x mg protein (n=6), which is more than twice higher than that previously reported in rat liver mitochondria. Label incorporation into fatty acids was, in mitochondria disrupted by freezing and thawing, much higher than in intact organelles thus suggesting a probable localization of this pathway inside mitochondria. Only a negligible acetyl-CoA incorporation into fatty acids occurs in the absence of ATP, Mg2+ or reduced pyridine nucleotides; NADH alone seems to be as effective as NADH + NADPH as a hydrogen donor for the reducing steps. CoASH, without effect up to 10 microM, showed a strong inhibition at higher concentrations. From the ratio of total radioactivity and radioactivity in carboxyl carbon it can be inferred that in eel-liver mitochondria only chain elongation of preexisting fatty acids occurs. A significant fatty acid chain elongation activity is also present when, instead of acetyl-CoA, [2-(14)C]malonyl-CoA is used as a carbon unit donor. Moreover, the synthesized fatty acids were actively incorporated into phopholipids, mainly phosphatidylcholine, phosphatidylethanolamine and sphyngomyelin.

Efficacy of a sucrose-formulated recombinant factor VIII used for 22 surgical procedures in patients with severe haemophilia A

A sucrose-formulated recombinant FVIII (rFVIII-SF) was investigated under clinical trial conditions during surgical procedures in previously treated patients (PTPs). Fifteen PTPs with severe haemophilia A (FVIII < or = 1%) underwent 22 surgical procedures. The procedures performed cover a spectrum from minor to major surgery. Haemostatic outcome was assessed by the investigators to be excellent in 16 procedures and good in the remaining six procedures. It is concluded that rFVIII-SF is efficacious and safe in severe haemophilia A patients undergoing minor or major surgery.

Endogenous tissue factor pathway inhibitor modulates thrombus formation in an in vivo model of rabbit carotid artery stenosis and endothelial injury

BACKGROUND

Tissue factor pathway inhibitor (TFPI) is the sole known inhibitor of the extrinsic coagulation pathway of physiological importance; however, its role in modulating thrombosis in vivo is still unclear.

METHODS AND RESULTS

Intravascular thrombosis was initiated by placing an external constrictor around endothelially injured rabbit carotid arteries (n=10). Carotid blood flow velocity was measured by a Doppler flow probe. After placement of the constrictor, cyclic flow reductions (CFRs), due to recurrent thrombosis, developed at the site of stenosis. Transstenotic TFPI plasma activity was measured in blood samples before induction of CFRs and after 30, 60, and 180 minutes of CFRs. TFPI plasma activity distal to the site of thrombosis was significantly lower than the corresponding proximal values at 30, 60, and 180 minutes of CFRs. In addition, a progressive decrease in TFPI plasma activity was observed in both the proximal and the distal samples, indicating consumption of TFPI during thrombus formation. In 10 additional rabbits, CFRs were abolished by administration of aspirin (10 mg/kg). In the animals in which aspirin abolished CFRs, endogenous TFPI was depleted by a bolus of a polyclonal antibody against rabbit TFPI, and the effects on restoration of CFRs were monitored. In 5 of 6 animals in which aspirin abolished CFRs, depletion of endogenous TFPI activity caused full restoration of CFRs.

CONCLUSIONS

The data of the present study support the involvement of endogenous TFPI in the process of thrombus formation in vivo and its active role in modulating arterial thrombosis.

Recombinant human, active site-blocked factor VIIa reduces infarct size and no-reflow phenomenon in rabbits

Oxygen free radicals induce de novo synthesis of tissue factor (TF), the initiator of the extrinsic pathway of coagulation, within the coronary vasculature during postischemic reperfusion. In the present study we wanted to assess whether TF expression might cause myocardial injury during postischemic reperfusion. Anesthetized rabbits underwent 30 min of coronary occlusion followed by 5.5 h of reperfusion. At reperfusion the animals received 1) saline (n = 8), 2) human recombinant, active site-blocked activated factor VII (FVIIai, 1 mg/kg, n = 8), or 3) human recombinant activated FVII (FVIIa, 1 mg/kg, n = 8). FVIIai binds to TF as native FVII, but with the active site blocked it inhibits TF procoagulant activity. The area at risk of infarction (AR), the infarct size (IS), and the no-reflow area (NR) were determined at the end of the experiment. FVIIai resulted in a significant reduction in IS and NR with respect to control animals (28.1 +/- 11.3 and 11.1 +/- 6.1% of AR vs. 59.8 +/- 12.8 and 24.4 +/- 2.7% of AR, respectively, P < 0.01), whereas FVIIa resulted in a significant increase in IS and NR to 80.1 +/- 13. 1 and 61.9 +/- 13.8% of AR, respectively (P < 0.01). In conclusion, TF-mediated activation of the extrinsic coagulation pathway makes an important contribution to myocardial injury during postischemic reperfusion.

Effects of recombinant active site-blocked activated factor VII in rabbit models of carotid stenosis and myocardial infarction

We tested the effects of human recombinant active site-blocked activated factor VII (rFVIIai) in a rabbit model of carotid artery thrombosis. Cyclic flow variations (CFVs), due to recurrent thrombus formation, were obtained in stenotic rabbit carotid arteries with endothelial injury. After 30 min of CFV, the animals received rFVIIai. If CFVs were abolished, animals were observed for 30 additional minutes, after which human recombinant activated factor VII was infused into the carotid artery to determine whether it could displace rFVIIai from tissue factor (TF), thus restoring CFV. An additional group of animals received rFVIIai to determine its duration of action. Recombinant FVIIai abolished CFVs in 8 of 9 rabbits (P < 0.01). This effect was reversible, as rFVIIa administration restored CFVs in all animals. A further study was initiated to assess whether TF-dependent reductions in coronary blood flow might contribute to the occurrence of myocardial injury during postischaemic reperfusion of rabbit hearts. Recombinant FVIIai resulted in significant reductions in both infarct size and no-reflow area, while rFVIIa produced a significant increase in both infarct size and no-reflow area. These data suggest that rFVIIai might be beneficial in patients with acute myocardial infarction undergoing reperfusion therapies.

Emerging antithrombotic treatments for acute coronary syndromes

In the last few years the hypothesis of coronary thrombosis, frequently triggered by plaque ulceration or fissuration, has gained wide acceptance as one of the key events in the pathophysiology of acute coronary syndromes. Plaque ulceration may activate both platelets and the coagulation cascade via exposure of a variety of substances, such as von Willebrand factor and tissue factor. It has been demonstrated that aspirin reduces mortality and improves the prognosis of patients with such syndromes. More recently, newer drugs have been identified for the treatment of acute coronary syndromes; in particular, platelet glycoprotein IIb/IIIa inhibitors have been found to be more effective than aspirin in a variety of clinical conditions, such as unstable angina, acute myocardial infarction, and coronary angioplasty. Other drugs with different mechanisms of action will be soon available for large scale clinical trials.

Activated platelets and leucocytes cooperatively stimulate smooth muscle cell proliferation and proto-oncogene expression via release of soluble growth factors

BACKGROUND

Previous studies indicate that platelets and leucocytes might contribute to the development of neointimal hyperplasia following arterial injury. The present study was aimed at further investigating the role of platelets and leucocytes, alone or in combination, in promoting vascular smooth muscle cell (SMC) proliferation in vitro, focusing on the relative contribution of different soluble growth factors released by these cells, and on the ability to induce proto-oncogene expression, such as c-fos.

METHODS

SMCs from rabbit aortas, made quiescent by serum deprivation, were stimulated with either activated platelets, leucocytes, or both, separated from SMCs by a membrane insert. SMC proliferation was evaluated by measuring the incorporation of 3H-thymidine. The relative contribution of different platelet-derived mediators to SMC growth was evaluated by adding either ketanserin, a 5-HT2 receptor antagonist, R68070, a TxA2 receptor antagonist, BN52021, a platelet activating factor (PAF) receptor antagonist, and trapidil, a platelet derived growth factor (PDGF) receptor antagonist. The role of different leucocyte sub-populations (neutrophils and monocytes + lymphocytes) was also determined in additional experiments.

RESULTS

SMC proliferation was significantly increased by activated platelets to 360 +/- 9% of control values (P < 0.05). This effect was reduced by ketanserin, R68070, BN 52021 or trapidil. Whole leucocytes, neutrophils or lymphocytes + monocytes also increased SMC proliferation with respect to control experiments. Simultaneous stimulation of SMCs by platelets and whole leucocytes was associated with a significant greater increase in SMC proliferation as compared to SMC stimulated with platelets or leucocytes alone. c-fos expression, almost undetectable in unstimulated SMCs, was markedly increased by activated platelets or leucocytes.

CONCLUSIONS

Activated platelets promote SMC proliferation in vitro via release of soluble mediators, including serotonin, thromboxane A2 PAF and PDGF; activated leucocytes also induce a significant SMC proliferation and exert an additive effect when activated together with platelets; SMCs stimulated with activated platelets and leucocytes show an early expression of the proto-oncogene c-fos.

Spontaneous spinal subdural hematoma in a young adult with hemophilia

Spontaneous spinal subdural hemorrhage is a rare clinical problem that usually manifests with a sudden onset of pain and paralysis. This article reports on an 18-year-old male with hemophilia A and cerebral palsy, who experienced a several month history of transient back, hip, and leg pain accompanied by gait difficulties that ultimately culminated in a more striking episode of lower extremity weakness, irritability, and diffuse pain involving the neck, back, and legs. In the absence of any clinical or radiographic evidence of hemarthrosis, osteomyelitis, or intracranial hemorrhage, imaging of the spine disclosed a large, apparently multicompartmentalized intraspinal lesion, consistent with old hemorrhage. This extended from the thoracic to the sacral region, with the largest extent at the lumbosacral junction. Following correction of factor VIII levels, surgical exploration was undertaken and demonstrated liquefied blood within the subdural space without violation of the underlying arachnoid. Because the chronic subdural blood flowed quite easily through the dural opening by simply angling the operating table, a limited exposure was required to achieve a substantial evacuation of the clot. This case calls attention to the often protean manifestations of this process, the potential for a chronic course to the clinical symptoms, and the possibility of achieving substantial clot evacuation and clinical recovery with a limited operative approach.

Clinical evaluation of recombinant factor IX

The pharmacokinetics, safety, and efficacy of recombinant factor IX (rFIX) have been evaluated in previously treated and untreated patients with hemophilia B. In a study of 56 previously treated patients, there was a total of 1,070 hemorrhages, which required 1,514 infusions of rFIX. Of the 1,070 episodes, 80% resolved after a single rFIX infusion. The majority of the remaining episodes requiring more than 1 infusion were either major or complicated hemorrhages. Eighty-seven percent of the 1,514 infusions were rated by the physicians or patients as providing an excellent or good response. These results are consistent with the efficacy data from other hemophilia product clinical trials. rFIX has also been administered as bolus doses or by continuous infusion in conjunction with 13 surgical procedures. Estimated blood loss during and after surgery was as expected when compared with blood loss for similar procedures in patients without hemophilia, and 97% of the clinical responses during and after surgery were rated by physicians or patients as excellent or good. Pharmacokinetic comparison of rFIX with one plasma-derived product showed a statistically significant lower recovery (28% less) of rFIX. The half-lives between the two products were comparable. Common adverse events associated with rFIX treatment have been comparable to other factor IX products. As expected, there has been no evidence of viral transmission by rFIX.

Antithrombotic effects of recombinant human, active site-blocked factor VIIa in a rabbit model of recurrent arterial thrombosis

The extrinsic coagulation pathway is activated when circulating factor VII (FVII) gains access to tissue factor (TF) exposed as a consequence of vascular injury. Increasing evidence indicates that this TF-dependent activation of the coagulation plays an important role in the pathophysiology of intravascular thrombus formation. In the present study, we tested the effects of recombinant human, active site-blocked activated FVII (FVIIai) in a rabbit model of carotid artery thrombosis. Cyclic flow variations (CFVs), due to recurrent thrombus formation, were obtained in stenotic rabbit carotid arteries with endothelial injury. Carotid blood flow velocity was measured by a Doppler flow probe. After 30 minutes of CFVs, the animals received FVIIai (100 microg x kg(-1) x min(-1) intracarotid infusion for 10 minutes, n=9). If CFVs were abolished, animals were followed for 30 additional minutes, after which recombinant human activated FVII (FVIIa) was infused into the carotid artery (100 microg x kg(-1) x min(-1) for 10 minutes) to determine whether FVIIai could be displaced from TF by FVIIa, thus restoring CFVs. To establish the duration of action of FVIIai, an additional group of animals received FVIIai at the same dose as above, and after CFVs were inhibited, they were followed until CFVs were restored or for up to 6 hours. To determine whether CFVs could be restored by epinephrine after their abolition with FVIIai, increasing doses of epinephrine were administered to a third group of 6 animals. FVIIai abolished CFVs in 8 of 9 rabbits (P<.01). This effect was reversible, as FVIIa administration restored CFVs in all animals. Prothrombin times and activated partial thromboplastin times did not change significantly throughout the study. One single 10-minute infusion exerted complete antithrombotic effects for at least 6 hours, despite the fact that at this time point, plasma FVIIai levels were well below threshold concentrations. Epinephrine restored CFVs in 3 of 6 animals in which CFVs were inhibited by FVIIai. FVIIai exerts potent antithrombotic effects in this model; these effects were prolonged even after FVIIai was almost completely cleared from the circulation, probably as a result of the tight binding of FVIIai to TF. Thus, FVIIai might represent an antithrombotic substance of potential interest.

Ceruloplasmin impairs endothelium-dependent relaxation of rabbit aorta

This study evaluated the effects of ceruloplasmin, the copper-containing blue oxidase of vertebrate plasma, on the relaxation of rabbit aortic rings after endothelial release of nitric oxide (NO). Ceruloplasmin at physiological, i.e., micromolar, concentrations inhibited relaxation of rabbit aorta induced by endothelium-dependent agonists like acetylcholine or ADP, whereas it was ineffective toward vasodilation due to direct stimulation of smooth muscle cells by nitroglycerin. The effect was reversible and specific for native, fully metalated ceruloplasmin, since relaxation was not impaired by the heat-treated or metal-depleted derivatives. A trapping mechanism, involving a direct interaction of NO or other NO-containing species (like nitrosothiols and iron-dinitrosyls) with the copper sites and/or with the free thiol of ceruloplasmin, could be safely excluded on the basis of spectroscopic and chemical analyses of the protein exposed to authentic NO, nitrosothiols, or iron-dinitrosyls. The data presented in this paper constitute the first evidence of impairment of the endothelium-dependent vasodilatation by a plasma protein and may shed some light on the still uncertain physiological role of ceruloplasmin.

Inhibition of leucocyte and platelet adhesion reduces neointimal hyperplasia after arterial injury

Restenosis following coronary angioplasty is though to result from migration and proliferation of medial smooth muscle cells. However, the factors that initiate this proliferation are still unknown. In a rabbit model of carotid artery injury, we tested the hypothesis that activated platelets and leucocytes might contribute to the development of neointimal hyperplasia. Following arterial injury, rabbits received either no treatment, R15.7, a monoclonal antibody against the leucocyte CD11/CD18 adhesion complex, aurintricarboxylic acid (ATA), a substance that inhibits platelet glycoprotein Ib-von Willebrand factor interaction, or the combination of R15.7 and ATA. After 21 days, the extent of neointimal hyperplasia was evaluated by planimetry on histological arterial sections. The area of neointima averaged 0.51 +/- 0.07 mm2 in control animals and it was significantly reduced by administration of either R15.7 or ATA alone to 0.12 +/- 0.05 and 0.20 +/- 0.01 mm2, respectively (p < 0.05 vs controls for both groups). The animals that received the combination of R15.7 and ATA showed a further reduction in neointimal hyperplasia, as compared to animals that received ATA alone (p < 0.05 vs ATA alone). These data indicate that platelets and leucocytes play an important role in the pathophysiology of neointimal hyperplasia in this experimental model. Interventions that reduce platelet and leucocyte adhesion to vessel wall might have beneficial effects in reducing restenosis following coronary angioplasty.

Monoclonal antibody against tissue factor shortens tissue plasminogen activator lysis time and prevents reocclusion in a rabbit model of carotid artery thrombosis

BACKGROUND

Tissue factor (TF)-dependent activation of the coagulation is important in the pathophysiology of intravascular thrombus formation. We tested the effects of a monoclonal antibody against TF (AP-1) on lysis time induced by tissue-type plasminogen activator (TPA) and on reocclusion rate in a rabbit model of carotid artery thrombosis.

METHODS AND RESULTS

Intravascular thrombosis was obtained by placing an external constrictor around carotid arteries with endothelial injury. Carotid blood flow velocity ws measured continuously with a Doppler flow probe. Thirty minutes after thrombus formation, the rabbits received either AP-1 (0.15 mg/kg IV, n=8) or placebo (n=8). All rabbits also received TPA (80 microg/kg bolus plus 8 microg x kg(-1) x min(-1) infusion for up to 90 minutes or until reperfusion was achieved) and heparin (200 U/kg IV as a bolus). At reperfusion, TPA was discontinued, and the rabbits were followed for an additional 90 minutes. AP-1 shortened lysis time from 44+/-8 minutes (mean+/-SEM) in control rabbits to 26+/-7 minutes in AP-1 rabbits (P<.01). Reocclusion occurred in all control rabbits in 10+/-3 minutes, whereas it occurred in only two of eight AP-1 treated rabbits in 72 and 55 minutes (P<.01). No changes in prothrombin time and ex vivo platelet aggregation in response to various agonists were observed after AP-1 administration, indicating the absence of systemic effects by this antibody.

CONCLUSIONS

TF exposure and activation of the extrinsic coagulation pathway play an important role in prolonging lysis time and mediating reocclusion after thrombolysis in this model. AP-1, a monoclonal antibody against TF, might be suitable as adjunctive therapy to TPA.

[Effect of platelets and leukocytes on in vitro proliferation of muscle cells: role of platelet-derived chemical mediators]

Some evidence indicate that platelets (PLTs) and leukocytes might contribute to the development of neointimal hyperplasia following arterial injury, via release of several growth factors. To study the relative contribution of these cells and of growth factors released in consequence of activation, smooth muscle cells (SMCs), isolated from the aorta of New Zealand White rabbits, were grown in Dulbecco's medium containing 10% fetal calf serum (FCS). At 70% confluence, SMCs were made quiescent by removing FCS from the medium. Twenty-four hours later, the cells were stimulated with activated platelets, neutrophils, lymphocytes+monocytes, whole leukocytes and platelets + whole leukocytes. Then, 1 microCi of O3H-thymidine were added to SMC cultures to evaluate the degree of proliferation. Relative contribution of different PLT-derived mediators to SMC growth was evaluated by adding either ketanserin, a 5-HT2 receptor antagonist, ridogrel, a thromboxane A2 (TxA2) receptor antagonist, BN52021, a platelet activating factor (PAF) receptor antagonist, and trapidil, a platelet-derived growth factor (PDGF) receptor antagonist, or all antagonists together. SMC proliferation was significantly increased by platelet activation. This effect was reduced by adding either ketanserin, ridogrel, BN 52021 or trapidil. Neutrophils, lymphocytes + monocytes and whole leukocytes also increased SMC proliferation. Simultaneous stimulation of SMCs by platelets and whole leukocytes was associated with a significant increase in SMC proliferation as compared to platelets or leukocytes alone. Thus, TxA2, 5-HT, PAF, and PDGF all contribute to SMC proliferation in vitro. Adding all antagonist together resulted in an additive antiproliferative effect. Leukocytes are also important in SMC proliferation. Interaction between platelets and leukocytes may play a pivotal role in the modulation of this phenomenon.

[Inactivated factor VII exercises a powerful antithrombotic activity in an experimental model of recurrent arterial thrombosis]

The extrinsic coagulation pathway is activated when tissue factor (TF) is exposed as a consequence of arterial damage. TF binds to factor VII (FVII) or activated FVII (FVIIa), generating a complex that activates both FX and FIX, ultimately leading to thrombin formation. To determine whether inhibition of FVII binding to TF would result in antithrombotic effects, active site-blocked FVIIa (FVIIai) was used in a rabbit model of intravascular thrombus formation. In addition, to study the interaction between extrinsic coagulation pathway activation and platelet aggregation, in the same model of intravascular thrombus formation, recombinant human FVIIa was administered in antiplatelet-treated rabbits. Cyclic flow variations (CFVs), due to recurrent thrombus formation, were initiated by placing an external constrictor around the endothelially-injured rabbit carotid arteries (Folt's model). Carotid blood flow was measured continuously by a Doppler flow probe placed proximally to the constrictor. CFVs were induced in 29 New Zealand White rabbits. After CFVs were observed for 30 min, the animals were randomly divided in four groups: 5 animals received via a small catheter (26G) placed proximally to the stenosis, an intra-arterial infusion of human recombinant FVIIai (0.1 mg/kg/min for 10 min); 9 animals received AP-1, a monoclonal antibody against rabbit TF (0.1 mg/kg i.v. bolus); 7 animals received ridogrel, a dual thromboxane A2 synthetase inhibitor and thromboxane A2 receptor antagonist (10 mg/kg i.v. bolus); finally, 8 rabbits received aurintrycarboxilic acid (ATA), an inhibitor of platelet glycoprotein Ib/von Willebrand factor interaction (10 mg/kg i.v. bolus). FVIIai abolished CFVs in 5 of 5 animals (CFV frequency minutes 0 cycles/hour; p < 0.05; carotid blood flow velocity minutes 106 +/- 9% of the baseline values; NS vs baseline). AP-1 abolished CFVs in 7 of 9 animals (CFV frequency minutes 0 cycles/hour; p < 0.05; carotid blood flow velocity minutes 58 +/- 35% of the baseline values; NS vs baseline). Finally, in all the animals receiving ridogrel or ATA CFVs were abolished (CFV frequency 0 cycles/hour; p < 0.05 in both groups; carotid blood flow velocity, respectively 62 +/- 32 and 66 +/- 40% of the baseline values; NS vs baseline in both groups). Thirty minutes following inhibition of CFVs, in the FVIIai treated rabbits, human recombinant FVIIa was infused, via the small catheter placed proximally to the stenosis, at the dose of 0.1 mg/kg/min for 10 min. In the other three groups, FVIIa, at the same dose, was infused i.v. Infusion of FVIIa restored CFVs in all FVIIai treated animals and in 6 of 7 AP-1 treated animals, thus indicating that AP-1 and FVIIai bindings to TF was competitive and was replaced by FVIIa. Infusion of FVIIa failed to restore CFVs in ridogrel e ATA treated rabbits (1 of 7 and 0 of 8 rabbits, respectively), showing that activation of extrinsic coagulation by FVIIa was overcome by inhibition of platelet function. Activated partial thromboplastin time, and ex vivo platelet aggregation in response to ADP and thrombin, were not different after FVIIai infusion, while prothrombin time was slightly but significantly prolonged as compared to baseline values. Thus, FVII-VIIa plays an important role in initiating thrombus formation in vivo. Administration of FVIIai exerts a potent antithrombotic effects in this model without affecting systemic coagulation. In addition, in this model platelets exert an important role in arterial thrombosis, since in the presence of inhibition of platelet function, activation of the extrinsic coagulation pathway failed to restore thrombus formation.

Effects of tissue factor induced by oxygen free radicals on coronary flow during reperfusion

Tissue factor is a transmembrane protein that activates the extrinsic coagulation pathway by binding factor VII. Endothelial cells, being in contact with circulating blood, do not normally express tissue factor. Here we provide evidence that oxygen free radicals induce tissue factor messenger RNA transcription and expression of tissue factor procoagulant activity in endothelial cells in culture. Isolated, perfused rabbit hearts exposed to exogenous oxygen free radicals also showed a marked increase in tissue factor activity within the coronary circulation. Furthermore, in ex vivo and in vivo hearts subjected to ischemia and reperfusion, a condition associated with a production of oxygen free radicals in large amounts, a marked increase in tissue factor activity occurred. This phenomenon could be abolished by oxygen radical scavengers. This increase in tissue factor activity during postischemic reperfusion was accompanied by a significant decrease in coronary flow, suggesting that increase in tissue factor activity with the consequent activation of the coagulation cascade might impair coronary flow during reperfusion and possibly contribute to the occurrence of reperfusion injury.

Aurintricarboxylic acid reduces platelet deposition in stenosed and endothelially injured rabbit carotid arteries more effectively than other antiplatelet interventions

In the present study we tested the effects of different antithrombotic interventions on platelet deposition in experimentally-stenotic rabbit carotid arteries with endothelial injury. Platelet deposition, quantitated by labeling autologous platelets with 111In-oxine, was significantly reduced compared to control animals by all interventions tested, i.e., R 68070, a drug with thromboxane A2 synthase and receptor blocking properties, BN 52021, a PAF receptor antagonist, aurintricarboxylic acid (ATA), an inhibitor of platelet glycoprotein (Gp) Ib/von Willebrand factor (vWf) interaction, AZ-1, a monoclonal antibody against rabbit GP IIb/IIIa, the platelet receptor for fibrinogen, and AP-1, a monoclonal antibody against rabbit tissue factor. ATA was significantly more effective than all the other interventions in reducing platelet deposition in the stenotic vessels. We conclude that inhibition of Gp Ib/vWf interaction may be a more suitable target for antithrombotic therapy under conditions of high shear stress, like those produced in this model.

Pharmacokinetics of zidovudine and didanosine during combination therapy

While the combination of zidovudine and didanosine is used in HIV-infected patients with more advanced disease, the possibility of a pharmacokinetic interaction between these two drugs remains controversial. Zidovudine doses of 50, 100, and 200 mg, combined with 67, 167, and 250 mg of didanosine were evaluated in 11 asymptomatic HIV-infected patients after receiving 24 weeks of combination therapy in AIDS Clinical Trials Group protocol 143. The pharmacokinetic parameters of zidovudine and didanosine were similar to those obtained with each drug given as monotherapy in other previously published studies. The renal clearance and urinary recovery of glucuronidated zidovudine was reduced when zidovudine was given in combination with didanosine, possibly due to competition for renal tubular secretion. These data suggest that no clinically important pharmacokinetic interaction occurs when zidovudine and didanosine are given together.

A monoclonal antibody against rabbit tissue factor inhibits thrombus formation in stenotic injured rabbit carotid arteries

Tissue factor (TF) is a transmembrane protein that binds factor VII/VIIa, thus activating the extrinsic blood coagulation pathway. Since this pathway appears to be involved in the formation of intravascular thrombi, the anti-rabbit TF monoclonal antibody, AP-1, was produced and tested as an antithrombotic agent in a rabbit model of recurrent intravascular thrombosis. In this model, a plastic constrictor is positioned around the injured rabbit carotid arteries, and flow is monitored with a Doppler flow probe. This produces cyclic flow variation (CFV) in the carotid artery, which is caused by recurrent formation and dislodgment of thrombi at the site of the stenosis. After monitoring CFV pattern for 30 minutes, AP-1 was infused intravenously into nine rabbits at doses of 0.05 to 1.5 mg/kg body weight, and a control monoclonal antibody that does not react with rabbit TF was infused into four additional rabbits. In all rabbits receiving AP-1, CFV was abolished, and a steady normal blood flow was restored, indicating that thrombus formation had been blocked by AP-1. By contrast, in all rabbits that received the control monoclonal antibody, CFV continued unaltered. There was no change in the partial thromboplastin time and ex vivo platelet aggregation to several different agonists after infusion of AP-1, indicating an absence of systemic effects on the coagulation process. We conclude that activation of the extrinsic coagulation pathway has a key role in triggering intravascular thrombosis and that an anti-TF monoclonal antibody is an effective antithrombotic agent that could have therapeutic potential for humans.

Short-term and long-term role of platelet activating factor as a mediator of in vivo platelet aggregation

BACKGROUND

Platelet activating factor (PAF) is a phospholipid released upon stimulation by a variety of cells and has been implicated in several pathophysiological events such as asthma and inflammatory diseases. However, although the ability to aggregate platelets in vitro was the first biological activity ascribed to PAF, its role in contributing to the in vivo formation of arterial thrombi has not been thoroughly clarified.

METHODS AND RESULTS

Intravascular platelet aggregation was initiated in two different animal models of arterial stenosis and endothelial injury. An external constrictor was positioned around rabbit carotid arteries and canine coronary arteries. After placement of the constrictor, a typical pattern of flow developed in the stenotic vessels. This pattern of flow, characterized by progressive reductions of carotid or coronary blood flow followed by spontaneous or induced restorations of flow (cyclic flow variations, CFVs), is related to recurrent platelet aggregation at the site of the stenosis followed by dislodgment of the thrombus. After observing CFVs for 30 minutes, BN52021 (up to 1.2 mg/kg), a potent and selective PAF antagonist, was given intravenously to rabbits (n = 12) and dogs (n = 10). BN52021 completely inhibited CFVs in 10 of 12 rabbits, whereas it was relatively ineffective in abolishing CFVs in dogs (only 2 of 10 animals inhibited). This different effect of BN52021 was not explained by too small a dose of the drug to achieve a complete blockade of PAF receptors in dogs, since ex vivo platelet aggregation was completely inhibited in both rabbits and dogs in response to exogenous PAF at concentrations up to 10(-5) mol/L. In a second group of 10 dogs, the hypothesis that PAF may become an important mediator of CFVs in dogs only several hours after endothelial injury was tested. After 30 minutes of baseline CFVs, these animals received a bolus of BN52021 up to 1.2 mg/kg. After this treatment, CFVs were completely abolished in 2 of 10 animals. The remaining 8 dogs were followed for an additional 8-hour period, at the end of which a second bolus of BN52021 was given. At this time, BN52021 was effective, as CFVs were abolished in 6 of 8 animals. These effects of BN52021 at 8 hours were not the consequence of a cumulative dose of the compound, since ex vivo platelet aggregation in response to PAF returned to baseline values immediately before administering the second dose. To identify possible sources of PAF other than aggregating platelets at the site of arterial stenosis, dogs in a third group were killed after 30 minutes (n = 7) and after 8 hours (n = 8) of CFVs. Histological sections of the stenotic coronary artery showed a marked leukocyte infiltration in these arterial segments after 8 hours of CFVs, whereas sections from dogs killed after 30 minutes showed only moderate or no infiltration.

CONCLUSIONS

These data demonstrate that PAF plays an important role as a mediator of platelet aggregation in vivo in rabbits and dogs. In the canine model, PAF appears to become more important after leukocyte infiltration of the arterial wall, as it may contribute to initiating enough platelet activation to lead to cyclic flow variations at sites of arterial stenosis and endothelial injury. Data from the present study suggest that PAF antagonists may be used as antiplatelet agents.

The in vivo antiplatelet effects of thromboxane A2 synthase inhibitors are potentiated by simultaneous thromboxane A2/prostaglandin H2 receptor blockade

The aim of the present study was twofold: 1) to assess whether inhibition of thromboxane A2 (TxA2) synthase exerts more potent antiplatelet effects when applied concomitantly with TxA2 and prostaglandin (PG)H2 receptor blockade and 2) whether these effects are mediated through redirection of PG endoperoxides toward the synthesis of antiplatelet PGs, such as PGI2 and PGE2. Thus, cyclic flow variations (CFVs), due to recurrent platelet aggregation, were initiated in the stenotic, endothelially injured carotid arteries of 39 rabbits. After 30 min of CFVs, the animals received: 1) SQ29548 (up to 0.6 mg/kg bolus + 0.2 mg kg-1 hr-1, n = 13), a TxA2/PGH2 receptor antagonist; 2) dazoxiben (up to 15 mg/kg bolus + 5 mg kg-1 hr-1, n = 13), a TxA2 synthase inhibitor and 3) picotamide (up to 20 mg/kg bolus + 20 mg kg-1 hr-1, n = 13), a drug with simultaneous TxA2 synthase and receptor blocking properties. CFVs were abolished in 6, 7, and 12 animals treated with SQ29548, dazoxiben, and picotamide, respectively (P < .01 for picotamide versus SQ29548 and dazoxiben). The animals in which CFVs were not abolished by SQ29548 or dazoxiben received the other drug at the same dose. CFVs were abolished by dazoxiben in five of seven rabbits that initially did not respond to SQ29548 and by SQ29548 in five of six animals that did not respond to dazoxiben. All animals that responded to the combination of SQ29548 and dazoxiben, as well as those that responded to picotamide, received increasing intravenous infusions of epinephrine to restore CFVs.(ABSTRACT TRUNCATED AT 250 WORDS)

Measurement of HIV virus load and genotypic resistance by gene amplification in asymptomatic subjects treated with combination therapy

Quantification of viral load in HIV disease has become increasingly important as a marker of antiviral efficacy. We applied gene amplification techniques in vivo to asses antiretroviral activity of combination therapy. Five HIV-infected subjects, four of whom were drug naive, were administered combination therapy with zidovudine (ZDV) and didanosine (ddI). Plasma and peripheral blood mononuclear cells (PBMC) were obtained twice at baseline and then at 1, 3, 6, 9, and 12 months after the initiation of therapy. Results show that plasma HIV RNA copy number fell from 2,170 +/- 660/ml to undetectable at 1 month, with continued suppression at 12 months. HIV proviral DNA copy number decreased from 3.9 to 3.0 log10/10(6) CD4+ T cells at 12 months. Cell dilution cultures were positive in 4 of 5 subjects at baseline and in only 1 of 5 after 12 months. CD4+ T-cell count increased from 390 +/- 30/mm3 pretherapy, to 505 +/- 66/mm3 after 6 months of therapy, but returned to baseline levels after 12 months of therapy. No mutations were detected from PBMC DNA for codon 215 and 74 in the HIV pol gene from the drug-naive subjects. These findings suggest that gene amplification techniques can be used to study changes in viral load or genotype and can be applied in real time to samples from patients involved in clinical trials.

Endogenous prostaglandin endoperoxides may alter infarct size in the presence of thromboxane synthase inhibition: studies in a rabbit model of coronary artery occlusion-reperfusion

OBJECTIVES

The aim of this study was to assess whether prostaglandin endoperoxides, which continue to be formed in the setting of thromboxane A2 synthase inhibition, might influence the fate of ischemic myocardium in a model of coronary occlusion and reperfusion.

BACKGROUND

It was recently demonstrated that thromboxane A2 synthase inhibitors reduce ischemic myocardial injury through a redirection of prostaglandin (PG) endoperoxides toward the synthesis of "cardioprotective" prostaglandins, such as PGI2, PGE2 and PGD2. However, part of these prostaglandin endoperoxides may also stimulate a receptor, shared with thromboxane A2, mediating platelet aggregation and vasoconstriction.

METHODS

New Zealand White rabbits were subjected to 30 min of coronary occlusion, followed by 5.5 h of reperfusion. Fifteen minutes before reperfusion, the animals were randomized to receive 1) saline solution (control animals, n = 8); 2) SQ 29548, a potent and selective thromboxane A2/PGH2 receptor antagonist (n = 8); 3) dazoxiben, a selective thromboxane A2 synthase inhibitor (n = 8); 4) R 68070 (Ridogrel), a drug with dual thromboxane A2 synthase-inhibiting and thromboxane A2/PGH2 receptor-blocking properties (n = 8); or 5) aspirin + R 68070 (n = 8).

RESULTS

Dazoxiben and R 68070, but not SQ 29548, significantly reduced thromboxane B2 formation and increased plasma levels of 6-keto-PGF1 alpha, PGE2 and PGF2 alpha. Ex vivo platelet aggregation induced by U46619 (a thromboxane A2 mimetic) was inhibited by SQ 29548 and R 68070 but not by dazoxiben. In control animals, infarct size determined at the end of the experiment by triphenyltetrazolium chloride staining averaged 57.7 +/- 3.2% of the area at risk of infarction. The administration of SQ 29548 did not significantly reduce infarct size compared with that in control animals, whereas dazoxiben and R 68070 significantly reduced infarct size to 36.7 +/- 2.8% and 16.6 +/- 3.6% of area at risk of infarction, respectively (p < 0.001 vs. control values). In rabbits treated with R 68070, infarct size was also significantly smaller than that of dazoxiben-treated rabbits (p < 0.01). This protective effect of R 68070 was completely abolished when the drug was administered with aspirin, infarct size in this group averaging 59.7 +/- 1.6% (p = NS vs. control values). No differences in regional myocardial blood flow, systemic blood pressure, heart rate or extent of area at risk were observed among groups.

CONCLUSIONS

Thus, prostaglandin endoperoxides play an important role in modulating the cardioprotective effects of thromboxane A2 synthase inhibitors. The simultaneous inhibition of thromboxane A2 synthase and blockade of thromboxane A2/PGH2 receptors by R 68070 identify a pharmacologic interaction of potential therapeutic importance.

A multicenter study of viral hepatitis in a United States hemophilic population

Hemophilia A and B patients seen at nine US regional treatment centers were tested for serologic markers of hepatitis B virus (HBV), hepatitis C virus (HCV), and hepatitis delta virus (HDV) during 1987 and 1988. Because human immunodeficiency virus (HIV) infection, a potentially confounding variable, was present in 53% of the group, the population was divided by HIV status for analysis purposes. In the HIV-positive group (N = 382), less than 1% had not been infected with HBV, HCV, or HDV, whereas 75% had evidence of infection with HBV and 98% with HCV. HBsAg, a marker of active HBV infection, was present in 12% of subjects; 96% of these were HCV positive. Anti-HDV was detected in 35 subjects (9.1%); all were anti-HBc positive. Ten of the 35 (29%) also were positive for IgM anti-HDV, indicating current infection. All 10 were HBsAg positive and 7 of the 9 tested were HDV RNA positive. Severe/moderate hemophilia B patients were more likely to have experienced an HBV infection and to be anti-HDV positive than were similar hemophilia A patients (22% v 8%, P < .05). In the HIV-negative group (N = 345), the subjects were younger and had less severe hemophilia than the HIV-positive patients. No evidence of HBV, HCV, or HDV infection was found in 18%, whereas 33% had experienced HBV infection and 79% were anti-HCV positive. Within this group, 4% were HBsAg positive. All 13 subjects with anti-HDV (4% of the HIV-negative group) also possessed anti-HBc. One (7.7%) was IgM anti-HDV positive and the serum from another contained HDV RNA. Both of these individuals were HBsAg positive. As in the HIV-positive group, severe/moderate hemophilia B patients were more likely to be HBV and HDV positive than were hemophilia A patients (9% v 3%, P < .05). A prevalence study of viral hepatitis in a large US hemophilic population showed that active infection with HCV is common, occurring in 89% of all study patients regardless of HIV status. Evidence of active HBV infection was found in 8%; 19% of these were actively infected with HDV. HDV was more common in hemophilia B patients after controlling for disease severity.

The effects of calcium channel antagonist treatment and oxygen radical scavenging on infarct size and the no-reflow phenomenon in reperfused hearts

Calcium antagonists reduce ischemic injury, and anti-free-radical interventions may reduce reperfusion injury. However, the effects of treatment with both interventions have never been investigated. In the present study, anesthetized rabbits underwent 30 minutes of coronary artery ligation, which was followed by 5.5 hours of reflow. Eight animals in each group received: (1) the calcium antagonist gallopamil during ischemia, (2) the oxygen radical scavenger superoxide dismutase during reperfusion, (3) combined treatment with gallopamil and superoxide dismutase, and (4) saline solution. All groups were similar with respect to collateral flow during ischemia and extent of risk region. Infarct size averaged 60.2% +/- 5.5% of risk region in controls and was significantly smaller (p < 0.001) in rabbits that were treated with either gallopamil (28.1% +/- 3.4%) of superoxide dismutase (29.3% +/- 3.2%). Little further reduction in infarct size was observed with combination therapy (22.9% +/- 3.2% of risk region; p = NS). Superoxide dismutase had no effects on hemodynamics, whereas gallopamil significantly reduced heart rate, mean arterial pressure, and rate-pressure product. However, the reduction in infarct size that was observed in gallopamil-treated rabbits significantly exceeded the expected value in this group after corrections were made for changes in these determinants of ischemic injury. Therefore we investigated whether other factors may have contributed to the beneficial effects of gallopamil. In vitro the drug had no oxygen radical scavenging activity, nor did it exert antioxidant effects. In addition, gallopamil did not affect neutrophil function. In conclusion, in this acute model myocardial cell necrosis was significantly reduced either by administration of a calcium antagonist during ischemia or by removing oxygen radicals during reperfusion. However, superoxide dismutase administration did not further reduce infarct size when given to animals that had been treated with gallopamil. Since gallopamil has no direct effect on several mechanisms of reperfusion injury, these data suggest that calcium antagonists, by decreasing myocardial oxygen demand during ischemia, may indirectly reduce oxygen radical damage during subsequent reperfusion.

Endothelium-derived relaxing factor modulates platelet aggregation in an in vivo model of recurrent platelet activation

It has been shown that endothelium-derived relaxing factor (EDRF) may inhibit platelet aggregation in vitro through activation of platelet-soluble guanylate cyclase. To assess whether EDRF may also affect platelet function in vivo, intravascular platelet aggregation was initiated by placing an external constrictor around endothelially injured rabbit carotid arteries. Carotid blood flow velocity was measured continuously by a Doppler flow probe placed proximal to the constrictor. After placement of the constrictor, cyclic flow reductions (CFRs), due to recurrent platelet aggregation, developed at the site of the stenosis. After CFRs were observed for 30 minutes, a solution of authentic nitric oxide (NO, n = 10) was infused into the carotid artery via a small catheter placed proximally to the stenosis. Before infusion of NO, CFR frequency averaged 18.3 +/- 2.9 cycles per hour, and CFR severity (lowest carotid blood flow as percentage of baseline values) was 6 +/- 1%. NO completely inhibited CFRs in all animals, as shown by the normal and constant pattern of carotid blood flow (CFR frequency, 0 cycles per hour, p < 0.001; carotid blood flow, 92 +/- 5%, p = NS versus baseline). These effects were transient; CFRs were restored spontaneously within 10 minutes after cessation of NO infusion. After CFRs returned, S-nitroso-cysteine (S-NO-cys), a proposed form of EDRF, was infused into the carotid artery. S-NO-cys also abolished CFRs in all animals but at a significantly lower dose than NO (0.3 +/- 0.1 versus 12 +/- 4 nmol/min). The role of endogenously released EDRF in modulating in vivo platelet function was then tested in additional experiments. In 10 animals, endogenous release of EDRF was stimulated by infusing acetylcholine into the aortic root during CFRs. Infusion of acetylcholine was also associated with a complete inhibition of CFRs, similar to that observed during exogenous infusion of NO or S-NO-cys. These antithrombotic effects of acetylcholine were completely lost when EDRF synthesis was prevented by administration of the L-arginine analogue NG-monomethyl L-arginine (L-NMMA). Furthermore, in six additional rabbits the basal release of EDRF was blocked by L-NMMA after CFRs had been previously abolished with aspirin or the combination of aspirin and ketanserin, a serotonin S2 receptor antagonist. L-NMMA caused restoration of CFRs in all animals, indicating that even the basal release of EDRF is important in modulating platelet reactivity in vivo. Taken together, the data of the present study demonstrate that endogenous EDRF might importantly contribute to the modulation of platelet function in vivo.

Experimental carotid stenosis and endothelial injury in the rabbit: an in vivo model to study intravascular platelet aggregation

Previous studies have shown that experimental canine coronary artery stenosis associated with endothelial injury results in a typical pattern of coronary flow characterized by gradual decreases in coronary flow to almost zero values followed by restorations of flow to normal values. This pattern of flow, called cyclic flow reductions (CFRs), is the consequence of recurrent platelet aggregation at the site of the stenosis and endothelial injury and subsequent dislodgement of the thrombus. In the present study, platelet activation and aggregation in vivo was induced by placing an external constrictor around carotid arteries with endothelial injury in anesthetized rabbits. Carotid blood flow velocity was measured continuously with a Doppler flow probe positioned proximally to the constrictor. After placement of the constrictor, CFRs developed in 14 of 14 rabbits with a mean frequency of 16.5 +/- 2.3 cycles/h. CFRs were observed for 30 min, and the animals were treated with either an i.v. bolus of aspirin (10 mg/kg) or R 68070 (20 mg/kg), a drug with simultaneous TxA2 synthase and TxA2/PGH2 receptor blocking properties. Aspirin completely inhibited CFRs in 4 of 7 rabbits, whereas R 68070 eliminated CFRs in 7 of 7 animals. In the 3 animals that did not respond to aspirin, administration of ketanserin (0.25 mg/kg i.v.), a selective serotonin S2 receptor antagonist, completely abolished CFRs. Both aspirin and R 68070 resulted in a marked reduction in serum TxB2 formation and in a complete inhibition of ex vivo platelet aggregation in response to arachidonic acid, whereas aggregation in response to U46619, a TxA2 mimetic, was inhibited only in R 68070-treated rabbits.(ABSTRACT TRUNCATED AT 250 WORDS)