Inhibition of Factor XIa by Antithrombin I11

The inactivation of human factor XIa by human antithrombin III was studied under pseudo-first-order reaction conditions (excess antithrombin III) both in the absence and in the presence of heparin. The time course of inhibition was followed by using polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate. After electrophoresis, proteins were blotted onto nitrocellulose and stained either for glycoprotein or for antithrombin III using antibodies against antithrombin III. Concomitant with factor XIa inactivation, two new slower migrating bands, one of which represented the intermediate complex consisting of one antithrombin III complexed with factor XIa, appeared as a transient band. Complete inactivation resulted in a single band representing the complex of factor XIa with two antithrombin III molecules. Quantitative analysis of the time course of inactivation was accomplished by measurement of the disappearance of factor XIa amidolytic activity toward the chromogenic substrate S2366. Pseudo-first-order reaction kinetics were observed throughout. The rate constant of inactivation was found to be 10(3) M-1 s-1 in the absence of heparin and 26.7 X 10(3) M-1 s-1 in the presence of saturating amounts of heparin. From the kinetic data, a binding constant (Kd) of 0.14 microM was inferred for the binding of antithrombin III to heparin. The time course of inactivation and the distribution of the reaction products observed upon gel electrophoresis are best explained assuming a mechanism of inactivation in which the two active sites present in factor XIa are inhibited in random order (i.e., independent of each other) with the same rate constant of inhibition

Meizothrombin formation during factor Xa-catalyzed prothrombin activation:Formation in a purified system and in plasma

Meizothrombin and thrombin formation were quantitated during factor Xa-catalyzed activation of human prothrombin in reaction systems containing purified proteins and in plasma. In the purified system considerable amounts of meizothrombin accumulated when prothrombin was activated by factor Xa (with or without accessory components) under initial steady state conditions. The ratio of the rates of meizothrombin and thrombin formation was not influenced by variation of the pH, temperature, or ionic strength of the reaction medium. When 2-mu-M prothrombin was activated by the complete prothrombinase complex (factor Xa, factor Va, Ca2+, and phospholipid) 80-90% of the initially formed reaction product was meizothrombin. Lowering the prothrombin concentration from 2 to 0.03-mu-M caused a gradual decrease in the ratio of meizothrombin/thrombin formation from 5 to 0.6. When the phosphatidylserine content of the phospholipid vesicles was varied between 20 and 1 mol% and prothrombin activation was analyzed at 2-mu-M prothrombin the relative amount of meizothrombin formed decreased from 85 to 55%. With platelets, cephalin, or thromboplastin as procoagulant lipid, thrombin was the major reaction product and only 30-40% of the activation product was meizothrombin. We also analyzed complete time courses of prothrombin activation both with purified proteins and in plasma. In reaction systems with purified proteins substantial amounts of meizothrombin accumulated under a wide variety of experimental conditions. However, little or no meizothrombin was detected in plasma in which coagulation was initiated via the extrinsic pathway with thromboplastin or via the intrinsic pathway with kaolin plus phospholipid (cephalin, platelets, or phosphatidylserine-containing vesicles). Thus, thrombin was the only active prothrombin activation product that accumulated during ex vivo coagulation experiments in plasma

Downtown Waterville Feasibility Study Waterville, Maine

The Purpose and Need for this project is to: “Revitalize the Downtown to improve the aesthetics, support existing businesses and encourage economic growth, improve pedestrian and bicycle accommodations and provide adequate parking while maintaining vehicular capacity in the overall area.” Contributions and assistance in the completion of the study were provided by the City of Waterville, Colby College, the Maine Department of Transportation, and the General Public

Speckle Tracking Echocardiography for the Assessment of the Athlete's Heart: Is It Ready for Daily Practice?

PURPOSE OF REVIEW: To describe the use of speckle tracking echocardiography (STE) in the biventricular assessment of athletes' heart (AH). Can STE aid differential diagnosis during pre-participation cardiac screening (PCS) of athletes? RECENT FINDINGS: Data from recent patient, population and athlete studies suggest potential discriminatory value of STE, alongside standard echocardiographic measurements, in the early detection of clinically relevant systolic dysfunction. STE can also contribute to subsequent prognosis and risk stratification. Despite some heterogeneity in STE data in athletes, left ventricular global longitudinal strain (GLS) and right ventricular longitudinal strain (RV ɛ) indices can add to differential diagnostic protocols in PCS. STE should be used in addition to standard echocardiographic tools and be conducted by an experienced operator with significant knowledge of the AH. Other indices, including left ventricular circumferential strain and twist, may provide insight, but further research in clinical and athletic populations is warranted. This review also raises the potential role for STE measures performed during exercise as well as in serial follow-up as a method to improve diagnostic yield

Evaluatie van de rechter ventrikelfunctie tijdens inspanning bij atleten en patiënten met pulmonale hypertensie

It is increasingly recognized that the right ventricle (RV) is an important predictor of prognosis and exercise capacity in a broad range of cardiac and pulmonary vascular diseases. In healthy subjects with a normal pulmonary circulation, the hemodynamic load on the RV increases relatively more during exercise than that of the left ventricle (LV) and this disproportionate load is far greater in patients with pulmonary hypertension. Despite the notion that right heart function is an important contributor to cardiac output (CO) augmentation during exercise and, therefore, exercise capacity, RV function is generally only evaluated at rest. The purpose of this thesis is to characterize RV reserve and its interaction with the pulmonary circulation during exercise in a wide range of subjects, from patients with chronic thromboembolic pulmonary hypertension (CTEPH) and reduced RV functional reserve to endurance athletes (EAs) with super-normal RV performance during exercise. The general hypothesis is that in these different groups, RV dysfunction is more apparent under the hemodynamic stress of strenuous exercise as compared with resting conditions and that RV dysfunction may be an important constraint on CO augmentation and exercise capacity. We validated a novel cardiac magnetic resonance (CMR) imaging technique to assess biventricular volumes and function during strenuous exercise and free-breathing by comparing CMR measurements against an invasive reference technique. Interpretation of RV versus LV volumes requires careful definition of the exact respiratory time point for proper interpretation, both at rest and during exercise. Using CMR with simultaneous invasive pressure measurements we provide more evidence that exercise places a disproportionate load on the RV as compared to the LV, even in healthy subjects. During brief exercise, a healthy RV can cope with the increased work demands. However, after multiple hours of intense endurance exercise, the RV dilates and ejection fraction decreases. Further studies are needed to examine whether repeated bouts of strenuous endurance exercise may result in proarrhythmogenic RV remodeling in some athletes and whether exercise measurements may be useful to detect abnormalities in an early stage. In endurance athletes with documented ventricular arrhythmias (EA-VAs), RV contractile reserve during exercise is attenuated during exercise despite few abnormalities at rest. Therefore, RV stress testing may be promising as a non-invasive means of risk-stratifying athletes. In patients with pulmonary vascular disease, the changes in RV volumes and performance during exercise provide a better correlation with symptoms and objective metrics of exercise capacity than resting measures. Moreover, in CTEPH patients with normalized resting hemodynamics and RV function after pulmonary endarterectomy, impaired pulmonary vascular and RV functional reserve during exercise explains why exercise intolerance remains poor. Finally, we demonstrate that echocardiography is a feasible and accurate tool for the evaluation of pulmonary vascular and RV functional reserve during exercise. This is clinically very relevant given that echocardiography is the imaging modality of choice and provides support for the use of exercise evaluation to detect sub-clinical pulmonary vascular disease in clinical practice.status: publishe

To assess exertional breathlessness you must exert the breathless

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