Spatial Attentional Selection Modulates Early Visual Stimulus Processing Independently of Visual Alpha Modulations.

The capacity-limited human brain is constantly confronted with a huge amount of sensory information. Selective attention is needed for biasing neural processing towards relevant information and consequently allows meaningful interaction with the environment. Activity in the alpha-band has been proposed to be related to top-down modulation of neural inhibition and could thus represent a viable candidate to control the priority of stimulus processing. It is, however, unknown whether modulations in the alpha-band directly relate to changes in the sensory gain control of the early visual cortex. Here, we used a spatial cueing paradigm while simultaneously measuring ongoing alpha-band oscillations and steady-state visual evoked potentials (SSVEPs) as a marker of continuous early sensory processing in the human visual cortex. Thereby, the effects of spatial attention for both of these signals and their potential interactions were assessed. As expected, spatial attention modulated both alpha-band and SSVEP responses. However, their modulations were independent of each other and the corresponding activity profiles differed across task demands. Thus, our results challenge the view that modulations of alpha-band activity represent a mechanism that directly alters or controls sensory gain. The potential role of alpha-band oscillations beyond sensory processing will be discussed in light of the present results.

Cassava flour slurry as a low-cost alternative to commercially available gel for obstetrical ultrasound: a blinded non-inferiority trial comparison of image quality.

OBJECTIVE: To evaluate the quality of ultrasound images obtained with cassava flour slurry (CFS) compared with conventional gel in order to determine objectively whether CFS could be a true low-cost alternative. DESIGN: Blinded non-inferiority trial. SETTING: Obstetrical ultrasound unit in an academic medical centre. POPULATION OR SAMPLE: Women with a singleton pregnancy, undergoing anatomy ultrasounds. METHODS: Thirty pregnant women had standard biometry measures obtained with CFS and conventional gel. Images were compared side-by-side in random order by two blinded sonologists and rated for image resolution, detail and total image quality using a 10-cm visual analogue scale. Ratings were compared using paired t-tests. Participant and sonographer experience was measured using five-point Likert scales. MAIN OUTCOME MEASURES: Image resolution, detail, and total image quality. Participant experience of gel regarding irritation, messiness, and ease of removal. RESULTS: We found no significant difference between perceived image quality obtained with CFS (mean = 6.2, SD = 1.2) and commercial gel (mean = 6.4, SD = 1.2) [t (28) = -1.1; P = 0.3]. Images were not rated significantly differently for either reviewer in any measure, any standardized image or any view of a specific anatomic structure. All five sonographers rated CFS as easy to obtain clear images and easy for patient and machine cleanup. Only one participant reported itching with CFS. CONCLUSIONS: CFS produces comparable image quality to commercial ultrasound gel. The dissemination of these results and the simple CFS recipe could significantly increase access to ultrasound for screening, monitoring and diagnostic purposes in resource-limited settings. FUNDING: This study was internally funded by our department. TWEETABLE ABSTRACT: Low-cost homemade cassava flour slurry creates images equal to commercial ultrasound gel, improving access.

Moraxella catarrhalis induces CEACAM3-Syk-CARD9-dependent activation of human granulocytes.

The human restricted pathogen Moraxella catarrhalis is an important causal agent for exacerbations in chronic obstructive lung disease in adults. In such patients, increased numbers of granulocytes are present in the airways, which correlate with bacteria-induced exacerbations and severity of the disease. Our study investigated whether the interaction of M. catarrhalis with the human granulocyte-specific carcinoembryonic antigen-related cell adhesion molecule (CEACAM)-3 is linked to NF-κB activation, resulting in chemokine production. Granulocytes from healthy donors and NB4 cells were infected with M. catarrhalis in the presence of different inhibitors, blocking antibodies and siRNA. The supernatants were analysed by enzyme-linked immunosorbent assay for chemokines. NF-κB activation was determined using a luciferase reporter gene assay and chromatin-immunoprecipitation. We found evidence that the specific engagement of CEACAM3 by M. catarrhalis ubiquitous surface protein A1 (UspA1) results in the activation of pro-inflammatory events, such as degranulation of neutrophils, ROS production and chemokine secretion. The interaction of UspA1 with CEACAM3 induced the activation of the NF-κB pathway via Syk and the CARD9 pathway and was dependent on the phosphorylation of the CEACAM3 ITAM-like motif. These findings suggest that the CEACAM3 signalling in neutrophils is able to specifically modulate airway inflammation caused by infection with M. catarrhalis.

[Cost analysis of patient blood management]. / Kostenanalyse eines Patient-Blood-Management-Konzepts.

BACKGROUND: Patient blood management (PBM) is a multidisciplinary approach focusing on the diagnosis and treatment of preoperative anaemia, the minimisation of blood loss, and the optimisation of the patient-specific anaemia reserve to improve clinical outcomes. Economic aspects of PBM have not yet been sufficiently analysed. OBJECTIVES: The aim of this study is to analyse the costs associated with the clinical principles of PBM and the project costs associated with the implementation of a PBM program from an institutional perspective. MATERIALS AND METHODS: Patient-related costs of materials and services were analysed at the University Hospital Frankfurt for 2013. Personnel costs of all major processes were quantified based on the time required to perform each step. Furthermore, general project costs of the implementation phase were determined. RESULTS: Direct costs of transfusing a single unit of red blood cells can be calculated to a minimum of €147.43. PBM-associated costs varied depending on individual patient requirements. The following costs per patient were calculated: diagnosis of preoperative anaemia €48.69-123.88; treatment of preoperative anaemia (including iron-deficiency anaemia and megaloblastic anaemia) €12.61-127.99; minimising perioperative blood loss (including point-of-care diagnostics, coagulation management and cell salvage) €3.39-1,901.81; and costs associated with the optimisation of the tolerance to anaemia (including patient monitoring and volume therapy) €28.62. General project costs associated with the implementation of PBM were €24,998.24. CONCLUSIONS: PBM combines various alternatives to the transfusion of red blood cells and improves clinical outcome. Costs of PBM vary from institution to institution and depend on the extent to which different aspects of PBM have been implemented. The quantification of costs associated with PBM is essential in order to assess the economic impact of PBM, and thereby, to efficiently re-allocate health care resources. Costs were determined at a single university hospital. Thus, further analyses of both the costs of transfusion and the costs of PBM-principles will be necessary to evaluate the cost-effectiveness of PBM.

Evaluation of two, commercial, multi-dye, nucleic acid amplification technology tests, for HBV/HCV/HIV-1/HIV-2 and B19V/HAV, for screening blood and plasma for further manufacture.

BACKGROUND: The cobas TaqScreen MPX Test, version 2.0, a multiplex, multi-dye nucleic acid amplification technology (NAT) test from Roche was evaluated by two European Blood Banks, the German Red Cross Blood Donor Service, Frankfurt, Germany and Centro de Hemoterapia y Hemodonación de Castilla y León, Valladolid, Spain. In addition, the cobas TaqScreen DPX Test was evaluated for the simultaneous detection and quantitation of parvovirus B19 and the detection of hepatitis A virus (HAV). STUDY DESIGN AND METHODS: The performances of the two tests were evaluated regarding the analytical sensitivity, the reproducibility of the tests using samples containing low concentrations of each virus and cross-contamination using samples containing high titres of virus. RESULTS: The analytical sensitivity of the MPX Test, version 2.0, obtained by the German Red Cross Blood Donor Service was 1·1, 3·9 and 43·3 IU/ml for HBV, HCV and HIV-1, respectively. The comparable analytical sensitivity at Centro de Hemoterapia y Hemodonación de Castilla y León was 3·5, 17·6 and 50·6 IU/ml for HBV, HCV and HIV-1, respectively. The analytical sensitivity of the DPX test determined by the German Red Cross Blood Donor Service was 0·6 and 3·8 IU/ml for HAV and B19. CONCLUSION: These multiplex and multi-dye blood screening assays represent a flexible NAT screening system for mini-pools between 6 and 96 samples per pool and fulfil all requirements of the European Pharmacopoeia for HCV and B19V testing of plasma for fractionation. The inclusion of a new multi-dye technology means discriminatory assays are no longer required for either test thus improving workflow, turn-around time and minimize the risk of obtaining a reactive result for which the virus cannot be identified.

Behavioral performance follows the time course of neural facilitation and suppression during cued shifts of feature-selective attention.

A central question in the field of attention is whether visual processing is a strictly limited resource, which must be allocated by selective attention. If this were the case, attentional enhancement of one stimulus should invariably lead to suppression of unattended distracter stimuli. Here we examine voluntary cued shifts of feature-selective attention to either one of two superimposed red or blue random dot kinematograms (RDKs) to test whether such a reciprocal relationship between enhancement of an attended and suppression of an unattended stimulus can be observed. The steady-state visual evoked potential (SSVEP), an oscillatory brain response elicited by the flickering RDKs, was measured in human EEG. Supporting limited resources, we observed both an enhancement of the attended and a suppression of the unattended RDK, but this observed reciprocity did not occur concurrently: enhancement of the attended RDK started at 220 ms after cue onset and preceded suppression of the unattended RDK by about 130 ms. Furthermore, we found that behavior was significantly correlated with the SSVEP time course of a measure of selectivity (attended minus unattended) but not with a measure of total activity (attended plus unattended). The significant deviations from a temporally synchronized reciprocity between enhancement and suppression suggest that the enhancement of the attended stimulus may cause the suppression of the unattended stimulus in the present experiment.

[Potential of hematopoietic stem cells as the basis for generation of advanced therapy medicinal products]. / Potenzial hämatopoetischer Stammzellen als Ausgangsmaterial für Arzneimittel für neuartige Therapien.

Individualized, (stem) cell-based therapies of congenital and acquired illnesses are among the most exciting medical challenges of the twenty-first century. Before the full potential of such therapies can be achieved, many basic scientific and biotechnological questions remain to be answered. What is the ideal source for the generation of such cellular drugs is one of those issues. In many respects, hematopoietic stem cells fulfill the requirements for stem cells as starting material for novel cellular therapeutics, including the simple access to large amounts of stem cells, the availability of good phenotypic markers for their prospective isolation, and an extensive body of knowledge about the in vitro manipulation of these cells. This manuscript discusses the general and specific usability of hematopoietic stem cells as starting material for novel cellular therapeutics and presents some examples of hematological and nonhematological therapeutic approaches which are based on hematopoietic stem cells.

Sustained division of the attentional spotlight.

By voluntarily directing attention to a specific region of a visual scene, we can improve our perception of stimuli at that location. This ability to focus attention upon specific zones of the visual field has been described metaphorically as a moveable spotlight or zoom lens that facilitates the processing of stimuli within its 'beam'. A long-standing controversy has centred on the question of whether the spotlight of spatial attention has a unitary beam or whether it can be divided flexibly to disparate locations. Evidence supporting the unitary spotlight view has come from numerous behavioural and electrophysiological studies. Recent experiments, however, indicate that the spotlight of spatial attention may be divided between non-contiguous zones of the visual field for very brief stimulus exposures (&<100 ms). Here we use an electrophysiological measure of attentional allocation (the steady-state visual evoked potential) to show that the spotlight may be divided between spatially separated locations (excluding interposed locations) over more extended time periods. This spotlight division appears to be accomplished at an early stage of visual-cortical processing.

[Treatment recommendations for mechanical ventilation of COVID­19 patients]. / Behandlungsempfehlungen zur Beatmung von COVID­19-Patienten.

Background: Due to the novelty of COVID­19 there is lack of evidence-based recommendations regarding the mechanical ventilation of these patients. Objective: Identification and delineation of critical parameters enabling individualized lung and diaphragm protective mechanical ventilation. Material and methods: Selective literature search, critical evaluation and discussion of expert recommendations. Results: In the current literature a difference between ARDS in COVID­19 and classical ARDS is described; however, there are no evidence-based recommendations for dealing with this discrepancy. In the past parameters and approaches for a personalized mechanical ventilation strategy were already introduced and applied. Conclusion: Using the parameters presented here it is possible to individualize the mechanical ventilation of COVID­19 patients in order to adjust and increase its compatibility to the heterogeneous clinical presentation of the COVID­19 ARDS.

First Observations of Mycosphaerella pini on Scots Pine in Finland.

Red band needle blight of pines caused by Mycosphaerella pini (anamorph Dothistroma septosporum) has recently been recorded on Scots pine (Pinus sylvestris) at 14 rural districts in southern and central Finland. Scots pine is the most common and commercially most important tree species in Finland. Red bands with aggregations of conidial stromata on otherwise brown attached needles were frequently encountered on saplings and young trees in dense stands and sporadically on lower twigs of mature trees within 2 m of the ground. These symptoms and signs, typical for M. pini (1), were also observed on needles of P. contorta and P. cembra, which occur in Finland in low frequency. Symptoms of red band needle blight and abundant conidial stromata were found in March and April of 2008 after a mild and rainy winter. After this time, the frequency at which fresh acervuli were observed decreased. Conidia were isolated after squeezing conidial stromata into a drop of sterile water and rinsing out the drop onto water agar from where single conidia were picked up from under the microscope with a modified Pasteur pipette. The conidia were hyaline, smooth, thin walled, filiform, 2.0 to 2.7 (2.4) µm wide, and 15 to 37 (29.4) µm long. Germination of the conidia on water agar was 100%. The cultures grew slowly and reached a diameter of 4 to 10 mm within 3 weeks on modified orange serum agar (2) at 20°C and abundantly produced conidia. Complete sequences of the internal transcribed spacer (ITS) region including the 5.8S rRNA gene were obtained for three isolates from different rural districts: Hartola (61°34'N, 26°01'E), Kangasniemi (61°59'N, 26°39'E), and Suonenjoki (62°37'N, 27°07'E). These sequences are deposited in GenBank with Accession Nos. EU834294, EU834295, and EU834296 and are identical to each other and to more than 50 M. pini sequences in GenBank, including those of several Estonian and Austrian isolates. These isolates are deposited in the culture collection of the Finnish Forest Research Institute with identifiers Dot1, Dot2, and Dot8. Symptoms were reproduced after inoculation of 1-year-old Scots pine seedlings growing in seedling trays with 115 cm3 cavities. A conidial suspension (5 to 6·× 103 conidia ml-1) was prepared from two single-conidial cultures (Dot10 and Dot15), combined, and sprayed during July 2008 onto 192 seedlings until needles looked completely wet. Sixty-four seedlings were sprayed with distilled water as a control treatment. Seedlings were incubated outdoors in Suonenjoki and covered with a transparent plastic hood for the first 5 days after inoculation. The first symptoms (brown segments and red bands on needles) appeared on inoculated seedlings 1 month later, and conidial stromata appeared after another 2 to 4 weeks. M. pini was reisolated from the acervuli of 10 sample needles. Three months after inoculation, all inoculated seedlings showed symptoms while all noninoculated seedlings were healthy. It is possible that M. pini has spread recently from the south since it was identified for the first time in Estonia 2 years earlier (3). Although the Gulf of Finland separates Finnish pine forests from Estonian pine forests by approximately 50 to 100 km, spores may have been aerially disseminated over this distance. Alternatively, introduction of M. pini to Finland may have occurred on imported seedlings. References: (1) Anonymous. OEPP/EPPO Bull. 35, 303, 2005. (2) M. Hanso and R. Drenkhan. Plant Pathol. 57:170, 2008. (3) M. M. Müller et al. Mycol. Res. 98:593, 1994.

Sources of synchronized induced Gamma-Band responses during a simple object recognition task: a replication study in human MEG.

Natural stimuli are compiled of numerous features, which are cortically represented in dispersed structures. Synchronized oscillations in the Gamma-Band (>30 Hz; induced Gamma-Band Responses, iGBRs), are regarded as a plausible mechanism to re-integrate these regions into a meaningful cortical object representation. Using electroencephalography (EEG) it was demonstrated that the generators of iGBRs can be localized to temporal, parietal, posterior, and frontal areas. The present magnetoencephalogram (MEG) study intended to replicate these findings in order contribute to the ongoing debate regarding the possible functional difference of high-frequency signals as measured by both techniques. During a standard object recognition task we found an augmentation of the iGBR after the presentation of meaningful as opposed to meaningless stimuli at approximately 160-440 ms after stimulus onset. This peak was localized to inferior temporal gyri, superior parietal lobules and the right middle frontal gyrus. Importantly, most of these brain structures were significantly phase-locked to each other. The implications of these results are twofold: (1) they present further evidence for the view that iGBRs signify neuronal activity in a broadly distributed network during object recognition. (2) MEG is well suited to detect induced high-frequency oscillations with a very similar morphology as revealed by EEG recordings, thereby eliminating known problems with electroencephalographical methods (e.g. reference confounds). In contrast to the iGBR, the localization of event-related fields (ERFs) and evoked Gamma-Band Response (eGBRs) revealed generators in focal visual areas, and thus, seem to mirror early sensory processing.

The time course of cortical facilitation during cued shifts of spatial attention.

Adaptive behavior requires the rapid switching of attention among potentially relevant stimuli that appear in the environment. The present study used an electrophysiological approach to continuously measure the time course of visual pathway facilitation in human subjects as attention was shifted from one location to another. Steady-state visual evoked potentials (SSVEPs) were recorded to rapidly flickering lights at attended and unattended locations, and variations in SSVEP amplitude over time were calculated after a cue to shift attention. The build-up of cortical facilitation reflected in SSVEP amplitude was found to bear a close temporal relationship with the emergence of accurate target discriminations at the newly attended location.

Human gamma band activity and perception of a gestalt.

Neuronal oscillations in the gamma band (above 30 Hz) have been proposed to be a possible mechanism for the visual representation of objects. The present study examined the topography of gamma band spectral power and event-related potentials in human EEG associated with perceptual switching effected by rotating ambiguous (bistable) figures. Eleven healthy human subjects were presented two rotating bistable figures: first, a face figure that allowed perception of a sad or happy face depending on orientation and therefore caused a perceptual switch at defined points in time when rotated, and, second, a modified version of the Rubin vase, allowing perception as a vase or two faces whereby the switch was orientation-independent. Nonrotating figures served as further control stimuli. EEG was recorded using a high-density array with 128 electrodes. We found a negative event-related potential associated with the switching of the sad-happy figure, which was most pronounced at central prefrontal sites. Gamma band activity (GBA) was enhanced at occipital electrode sites in the rotating bistable figures compared with the standing stimuli, being maximal at vertical stimulus orientations that allowed an easy recognition of the sad and happy face or the vase-faces, respectively. At anterior electrodes, GBA showed a complementary pattern, being maximal when stimuli were oriented horizontally. The findings support the notion that formation of a visual percept may involve oscillations in a distributed neuronal assembly.

Alterations of purine salvage pathways during differentiation of rat heart myoblasts towards myocytes.

Enzyme activities of purine catabolism and salvage, the concentrations of high-energy phosphates and the reutilisation of purine bases and purine nucleosides were studied in rat heart myoblasts and myocytes. Rat heart myoblasts H9c2(2-1) were grown in Dulbecco's modified Eagle's minimum essential medium supplemented with 10% fetal calf serum. Reduction of fetal calf serum to 2% for 1 week resulted in a differentiation into myocytes with respect to their morphological features and their enzyme pattern. In differentiated myocytes, activity of 5'-nucleotidase was increased more than 2-fold, and AMP deaminase and creatine kinase activities were more than 10-fold elevated. The concentration of creatine phosphate in differentiated myocytes was doubled compared to that in myoblasts. The uptake into myoblasts and myocytes and the incorporation into adenine nucleotides was highest using adenosine, inosine and adenine uptake rates were intermediate, and hypoxanthine was utilised least. Differentiation of myoblasts into myocytes resulted in a slightly lower overall uptake of adenosine and adenine, whereas about 40% more inosine and hypoxanthine were utilised by myocytes. Increasing the phosphate concentration in the incubation medium up to 50 mmol/l resulted in a stimulation of uptake of all purine compounds tested. This stimulation was more pronounced in myoblasts.

Intracellular acidification by inhibition of the Na+/H+-exchanger leads to caspase-independent death of cerebellar granule neurons resembling paraptosis.

Potassium withdrawal is commonly used to induce caspase-mediated apoptosis in cerebellar granule neurons in vitro. However, the underlying and cell death-initiating mechanisms are unknown. We firstly investigated potassium efflux through the outward delayed rectifier K+ current (Ik) as a potential mediator. However, tetraethylammoniumchloride, an inhibitor of Ik, was ineffective to block apoptosis after potassium withdrawal. Since potassium withdrawal reduced intracellular pH (pHi) from 7.4 to 7.2, we secondly investigated the effects of intracellular acidosis. To study intracellular acidosis in cerebellar granule neurons, we inhibited the Na+/H+ exchanger (NHE) with 4-isopropyl-3-methylsulfonylbenzoyl-guanidine methanesulfonate (HOE 642) and 5-(N-ethyl-N-isopropyl)-amiloride. Both inhibitors concentration-dependently induced cell death and potentiated cell death after potassium withdrawal. Although inhibition of the NHE induced cell death with morphological criteria of apoptosis in light and electron microscopy including chromatin condensation, positive TUNEL staining and cell shrinkage, no internucleosomal DNA cleavage or activation of caspases was detected. In contrast to potassium withdrawal-induced apoptosis, cell death induced by intracellular acidification was not prevented by insulin-like growth factor-1, cyclo-adenosine-monophosphate, caspase inhibitors and transfection with an adenovirus expressing Bcl-XL. However, cycloheximide protected cerebellar granule neurons from death induced by potassium withdrawal as well as from death after treatment with HOE 642. Therefore, the molecular mechanisms leading to cell death after acidification appear to be different from the mechanisms after potassium withdrawal and resemble the biochemical but not the morphological characteristics of paraptosis.

Functional correlates of macroscopic high-frequency brain activity in the human visual system.

The present article reviews empirical findings of large-scale gamma oscillations in the human brain, in the context of their functional correlates. Evidence supporting the fact that high-frequency neuronal oscillations are involved in several aspects of visual processing is presented, with a focus on bottom-up and top-down visual feature processing, selective attention, and emotional evaluation. This evidence suggests that visual processing involves the integrated activity of wide spread neuronal assemblies that can be studied with respect to time course and topography, employing frequency-domain analyses. Possible mechanisms underlying these phenomena are considered. Furthermore, the effects of attention and motivation, as well as characteristics of experimental paradigms are discussed as determinants of reliability and validity of measures of high-frequency oscillations.

A transcriptional enhancer located between adult beta-globin and embryonic epsilon-globin genes in chicken and duck.

We have detected a transcriptional enhancer sequence downstream from the adult beta-globin (beta A-globin) genes of chicken and duck. DNA segments from the beta-globin coding and flanking sequences were cloned into expression vectors containing the SV40 promoter linked to either the T antigen gene or the cat gene. The expression of these genes was measured in a chicken erythroid cell line transfected with the recombinant plasmids. We found that segments located about 400 bp downstream from the poly(A) site of both the chicken and duck beta A-globin genes (and about 1.5 kb upstream from the embryonic epsilon-globin gene) stimulate transcription of the test genes about five-fold. In chicken essentially the same segment was also found by others to act as an erythroid cell-specific enhancer [Hesse et al., Proc. Natl. Acad. Sci. USA 83 (1986) 4312-4316; Choi and Engel, Nature 323 (1986) 731-734]. The sequence containing this enhancer is conserved in evolution. A high degree of homology, reaching 84% in a segment 180 bp in length, was found between chicken and duck despite an evolutionary divergence of 70 myr.

Endothelial cell lining of bioprosthetic heart valve materials.

To investigate the conditions for endothelial cell lining of glutaraldehyde-treated bioprosthetic heart valves, we examined in vitro the growth properties of endothelial cells on clinically used pericardial valve material and on glutaraldehyde-fixed pericardium treated with L-glutamic acid. To improve endothelial cell attachment to the valvular surface, we precoated both materials either with fibronectin or with fibrillar collagen (95% type I, 5% type III). Toxicity of glutaraldehyde, released from clinically used valve material, caused endothelial cell death, independent of the type of precoating. Treatment of the valve material with L-glutamic acid resulted in regular endothelial cell proliferation. We found that collagenous precoating, compared with fibronectin precoating, markedly enhanced endothelial cell proliferation and attachment (p less than 0.05). Maintenance of antithrombogenic potency of the seeded cells on L-glutamic acid-treated valve material was proved by regular release of prostacyclin. We conclude that bioprosthetic heart valve materials can be lined with endothelial cells if toxic glutaraldehyde released from the bioprostheses is eliminated.

Aprotinin decreases release of 6-keto-prostaglandin F1 alpha and increases release of thromboxane B2 in cultured human umbilical vein endothelial cells.

Use of the proteinase inhibitor aprotinin significantly improves hemostasis and reduces bleeding after operations in which extracorporeal circulation is used. The mechanism of action, however, has been only partially clarified. In this work we investigated whether aprotinin influenced the production and release of the eicosanoids prostacyclin, measured as the stable metabolite 6-keto-prostaglandin F1 alpha, and thromboxane A2, measured as the stable metabolite thromboxane B2, from endothelial cells. Human umbilical vein endothelial cells were incubated with different concentrations of aprotinin (5.5, 20, 55, and 100 mumol/L). The levels of 6-keto-prostaglandin F1 alpha and thromboxane B2 were measured at baseline and after thrombin stimulation. A concentration-dependent effect of aprotinin on 6-keto-prostaglandin F1 alpha synthesis was demonstrated. After incubation with 100 mumol/L of aprotinin, a 90% reduction in 6-keto-prostaglandin F1 alpha production was seen (31.69 versus 307.44 picograms per million cells; p less than 0.001). Conversely, thromboxane B2 production showed a 345% increase after incubation with aprotinin (287.80 versus 83.82 picograms per million cells; p less than 0.0001). Since 6-keto-prostaglandin F1 alpha inhibits and thromboxane B2 strongly enhances platelet aggregation, it appears that one mechanism of the clinically observed effectiveness of aprotinin lies in the altered ratio of 6-keto-prostaglandin F1 alpha: thromboxane B2 in endothelial cells, which leads to enhanced platelet aggregation and improved vessel sealing.