Endurance training modifies exercise-induced activation of blood coagulation: RCT

Randomized controlled trials (RCTs) on the topic of physical training and blood coagulation are rare and the effects are unclear. The aim of this study was to investigate whether endurance training adjusts blood coagulation and fibrinolysis at rest and after exercise. The study included 50 healthy untrained non-smokers randomized into training (TR 49 ± 6 years) or control group (CO 48 ± 6 years). Each subject performed an exercise test adjusted at 80 % individual anaerobic threshold (IAT) for 60 min before and after 12 weeks (80 % IAT: before TR 123 ± 20, CO 125 ± 26 W; after TR 148 ± 23 W, CO 127 ± 25 W; mean ± SD). Blood was taken at rest and after exercise to determine coagulation (e.g., aPTT, thrombin potential, TAT, F1+2, several coagulation factors) and fibrinolytic (e.g., tPA, PAI) parameters. The training intervention induced an elevation of physical capacity in TR by 17 % (rel. VO_2max) that led to a statistical relevant prolongation of aPTT at rest. Although absolute power output during the second exercise test was 20 % higher in TR, we detected an attenuated exercise-induced decrease of aPTT and attenuated increase of F1+2 after training. Resting levels of tPA- and PAI-Ag decreased slightly but not significantly after training. Exercise-induced changes were comparable after training in spite of higher power output in TR. Although the effects are small in healthy men, training modifies exercise-induced blood coagulation positively. The fact that exercise-induced changes in blood coagulation and fibrinolysis are rather attenuated or unchanged in the training group, in spite of a 20 % higher absolute power output during exercise, substantiates the adjusting effect of endurance training and the importance of physical fitness in primary prevention.     

In vitro fertilization. Do short-term changes in estrogen levels produce increased fibrinolysis?

High estrogen levels have been implicated as a cause of thrombosis. Patients undergoing in vitro fertilization (IVF) present an opportunity to study isolated estrogen effects on the coagulation system, since hormonal manipulation is used to achieve varying estrogen concentrations. We evaluated the effect of estrogen levels on the fibrinolytic and clotting systems of 32 patients undergoing IVF from whom venous samples were obtained during a period of several weeks at baseline and retrieval times. Flow cytometric studies were performed to assay platelet activation. Hemostasis markers measured thrombin-antithrombin complexes (TAT), fibrinogen, plasmin-alpha 2-antiplasmin complexes (PAP), plasminogen activator inhibitor (PAI-1), and D-dimer. A significant decrease in PAI-1 and an increase in PAP were observed at high estrogen levels, suggesting an increase in fibrinolytic potential. However, the products of fibrinolysis, as measured by D-dimer levels, decreased at high estrogen levels. No changes were seen in platelet activation indicators or TAT levels. The fact that a decrease in products of fibrinolysis was seen at high estrogen levels despite concurrent changes in PAI-1 and PAP that normally accompany increased fibrinolysis may be due to alterations in the overall balance of the fibrinolytic system or to a delay in onset of fibrinolysis.     

Associative conditioning with leg cycling and inspiratory resistance enhances the early exercise ventilatory response in humans

Repeated trials of hypercapnic exercise [P_ETCO₂=7 (1) mmHg] augment the increase in inspired minute ventilation and tidal volume (V_T) in the early phase of subsequent trials of unencumbered exercise alone. The increase in V_T in the first 20 s of exercise was correlated to the increase in V_T evoked during hypercapnic exercise trials, suggesting that the evoked increase in V_T during conditioning may be a factor in mediating associative conditioning. To test this hypothesis, inspiratory resistive loading (IRL) was employed to evoke an increase in V_T [V_T=0.4 (0.1) l_BTPS] during conditioning exercise trials [IRL+EX; P_ETCO₂=2 (1) mmHg]. IRL+EX associative conditioning elicited a significant augmentation of the early minute ventilation (+46%) and V_T (+100%) responses to subsequent unencumbered exercise. The latter was correlated to the evoked increase in V_T during associative conditioning with IRL+EX. The results support the hypothesis that an evoked increase in V_T during associative conditioning could be a factor in eliciting long-term modulation of minute ventilation in subsequent unencumbered exercise. The results further indicated that the modulation of ventilation early in exercise is not due to sensitisation to repeated trials of either IRL or exercise alone. Associative conditioning may shape the ventilatory response to exercise through a process of motor learning. Data are presented as mean (SEM) unless otherwise stated.     

Pure eccentric exercise does not activate blood coagulation

Eccentric exercise can cause skeletal muscle damage with ultrastructural disruption, inflammation and increased proteolytic enzyme activity. It may be possible that these changes are able to trigger blood coagulation in vivo. The aim of the study was to investigate changes in blood coagulation via the measurement of aPTT, the thrombin potential (total [TTP] and endogenous [ETP], both intrinsic [in] and extrinsic [ex]) and the thrombin generation (prothrombinfragment 1+2 [F1+2] and thrombin-antithrombin complex [TAT]) after pure eccentric exercise. Seventeen healthy non-smokers (28±6 years, VO₂-peak 59±7 ml/min/kg) underwent pure eccentric down jumps (9×28 isolated down jumps in 90 min, drop from a height of 55 cm), a cycle exercise (90% of the individual anaerobic threshold for 60–90 min) and a control experiment on different days. Blood samples were drawn after a 30-min rest, immediately, and 2 h after exercise. After the cycle exercise, a clear shortening by 12% (P<0.001) in aPTT and an increase in TTPin (13%; P<0.05) and TAT (33%; P<0.05) in comparison to the control experiment were seen, while after eccentric exercise only minimal changes in aPTT and thrombin potential (TTPin, ETPin) and no thrombin generation (F1+2 and TAT) were found. In contrast to concentric dynamic exercise, e.g. cycle ergometry, only insignificant changes in thrombin potential and no thrombin generation could be observed after skeletal muscle damage induced by pure eccentric exercise. It can be concluded that the mechanical impact associated with eccentric exercise does not activate blood coagulation.     

Reliability,reproducibility and validity of the individual anaerobic threshold

Summary The individual anaerobic threshold (IAT) has been defined as the highest metabolic rate at which blood lactate (La) concentrations are maintained at a steady state during prolonged exercise. The validity of this definition, however, has not been substantiated. Eleven men [maximum oxygen uptake ( ), mean (SD), 57.8 (6.9) ml·kg^–1 · min^–1) did two maximal incremental cycle exercise tests (30 W and 4 min per step). Blood was sampled repeatedly during exercise and for 9 min during the subsequent recovery period with light activity. The subjects then exercised at the power output equivalent of IAT for 45 min, until they could no longer continue or until rectal temperature reached 39°C. Subjects performed two additional exercise tests. The intensity of these tests depended upon the LA and acid-base responses during the last 15 min of at least 30 min of exercise at IAT. If a steady state was achieved (La, pH and PCO₂ changed by less than 0.5 mmol·l^–1, 0.005 pH units and 0.3 kPa, respectively) or decreasing La and increasing pH values were observed, then the second test was performed at IAT + 5% and the third session at either IAT + 2.5% or +7.5% . Conversely if a steady state was not achieved during exercise at the calculated IAT, the intensity of the second test was set at IAT–5% . Depending on the La and acid-base responses during this test, the final session was performed at either IAT –2.5% or –7.5% . Test-retest reliability for the determination of IAT was high (r = 0.98; estimated SE was 8 W or about 2% ) and the method was reproducible [mean (SD); 240.3 (41.7) W for test 1 and 236.6 (42.9) W for test 2]. However, only 4 subjects completed at least 30 min of exercise at IAT with steady-state La and acid-base responses. None of these subjects showed steady-state responses at +5% above IAT, and only 1 met the criteria at +2.5% above IAT. Therefore, for these individuals the incremental exercise test underestimated the true IAT by less than 5% . For the other 7 subjects, 4 met the steady-state criteria at both –5% and –2.5% below the calculated IAT, suggesting the true IAT was overestimated by less than 2.5% . For 2 of the remaining subjects, the incremental exercise test over-estimated the true IAT by at least 7.5% . Therefore, the maximal incremental exercise test followed by a light active recovery period will produce a reliable and reproducible estimate of IAT which is valid for the majority of subjects. However, since the method overestimates the true IAT for some individuals, the procedure cannot be assumed (without verification) to be valid for all subjects.     

Alterations in coagulatory and fibrinolytic systems following an ultra-marathon

Purpose

The aim of this study was to examine coagulatory and fibrinolytic responses to the Western States Endurance Run (WSER, June 23 to 24, 2012). The WSER is a 161-km (100 mile) trail foot race through the Sierra Nevada Mountains that involves 6,030 m of climb and 7,001 m of descent.

Methods

We examined 12 men and 4 women [mean (95 % CI), age 44.6 years (38.7–50.6)] who completed the race (24.64 h; range 16.89–29.46). Blood samples were collected the morning before the race, immediately post-race, and 1 (D1) and 2 (D2) days post-race (corresponding to 51–54 h and 75–78 h from the start of the race, respectively). Hypercoagulable state was characterized by prothrombin fragment 1+2 (PTF 1+2) and thrombin–antithrombin complex (TAT). Fibrinolytic state was assessed by plasminogen activator inhibitor antigen (PAI-1 Ag), tissue plasminogen activator antigen (tPA Ag), and d-Dimer. Muscle damage was assessed by serum creatine kinase (CK) and myoglobin concentrations.

Results

Significant (P ≤ 0.05) increases were observed immediately post-race for thrombin generation markers, PTF 1+2 (3.9-fold) and TAT (2.4-fold); markers of fibrinolysis, tPA Ag (4.0-fold), PAI-1 Ag (4.5-fold), and d-Dimer (2.2-fold); and muscle damage markers, CK (154-fold) and myoglobin (114-fold). Most markers continued to be elevated at D1, as seen by PTF 1+2, TAT (1.5- and 1.3-fold increase at D1), and d-Dimer (2.5- and 2.1-fold increase at D1 and D2, respectively). Additionally, PTF 1+2:tPA and TAT:tPA ratios, which assessed balance between coagulation and fibrinolysis, were slightly, but significantly increased at D1 (69 and 36 %) and D2 (19 and 31 %). CK and myoglobin also remained elevated at D1 (54- and 7-fold) and D2 (25- and 2-fold) time points.

Conclusion

The WSER produced extensive muscle damage and activated the coagulation and fibrinolytic systems. Since we observed a slight imbalance response between the two systems, a limited potential for thrombotic episodes is apparent in these highly trained athletes.     

Alterations of coagulation and fibrinolysis in patients with angioedema due to C1-inhibitor deficiency

Patients with functional deficiency of C1-inhibitor (C1-INH) suffer from recurrent acute attacks (AA) of localized oedema associated with activation of the contact system, complement and fibrinolysis. To unravel further the role of coagulation and fibrinolysis in the pathophysiology of C1-INH deficiency, we performed simultaneous thrombin and plasmin generation measurements in plasma from patients with hereditary angioedema (HAE) due to C1-INH deficiency during AA (n = 23), in remission (R) (n = 20) and in controls (n = 20). During AA thrombin generation after in-vitro activation of plasma was higher than in controls, as demonstrated by shorter thrombin peak-time (P < 0·05), higher thrombin peak-height (P < 0·001) and increased area under the curve (AUC) (P < 0·05). Additionally, elevated levels of prothrombin fragment 1+2 (P < 0·0001) were observed in non-activated plasma from the same patients. In contrast, in activated plasma from patients during AA plasmin generation estimated as plasmin peak-height (P < 0·05) and plasmin potential (P < 0·05) was reduced, but non-activated plasma of the same patients showed elevated plasmin-anti-plasmin (PAP) complexes (P < 0·001). This apparent discrepancy can be reconciled by elevated soluble thrombomodulin (sTM) (P < 0·01) and thrombin activatable fibrinolysis inhibitor (TAFI) in patients during AA providing possible evidence for a regulatory effect on fibrinolysis. Plasminogen activator inhibitor-1 (PAI-1) was reduced in patients during AA indicating, together with the observed reduction of plasmin generation, the consumption of fibrinolytic factors. In conclusion, our results support the involvement of coagulation and fibrinolysis in the pathophysiology of HAE and show the possible application of simultaneous measurement of thrombin and plasmin generation to evaluate different clinical conditions in HAE patients.     

Blood lactate responses in incremental exercise as predictors of constant load performance

Summary Seven trained male cyclists ( =4.42±0.23 l·min⁻¹; weight 71.7±2.7 kg, mean ± SE) completed two incremental cycling tests on the cycle ergometer for the estimation of the “individual anaerobic threshold” (IAT). The cyclists completed three more exercises in which the work rate incremented by the same protocol, but upon reaching selected work rates of approximately 40, 60 and 80% , the subjects cycled for 60 min or until exhaustion. In these constant load studies, blood lactate concentration was determined on arterialized venous ([La⁻]a_v) and deep venous blood ([La⁻]_v) of the resting forearm. The a_v-v lactate gradient across the inactive forearm muscle was −0.08 mmol·l⁻¹ at rest. After 3 min at each of the constant load work rates, the gradients were +0.05, +0.65* and +1.60* mmol·l⁻¹ (*P<0.05). The gradients after 10 min at these same work rates were −0.09, +0.24 and +1.03* mmol·l⁻¹. For the two highest work rates taken together, the lactate gradient was less at 10 min than 3 min constant load exercise (P<0.05). The [La⁻]a_v was consistently higher during prolonged exercise at both 60 and 80% than that observed at the same work rate during progressive exercise. At the highest work rate (at or above the IAT), time to exhaustion ranged from 3 to 36 min in the different subjects. These data showed that [La⁻] uptake across resting muscle continued to increase to work rates above the IAT. Further, the greater a_v-v lactate gradient at 3 min than 10 min constant load exercise supports the concept that inactive muscle might act as a passive sink for lactate in addition to a metabolic site.     

Blood coagulation and fibrinolysis in healthy, untrained subjects: effects of different exercise intensities controlled by individual anaerobic threshold

The influence of different exercise intensities on haemostasis in healthy, untrained subjects has not been intensively studied. We investigated untrained subjects for alterations in coagulation and fibrinolysis induced by two exercise intensities, precisely controlled by individual anaerobic threshold (IAT). Twenty-five healthy, untrained non-smokers (age 25?±?3?years; relative VO₂ peak 43.1?±?5.2?ml/kg/min) underwent exercise tests at 80% (moderate) and 100% (strenuous) of IAT for 60?min. Blood samples were taken after 30?min rest and immediately after exercise. The present results reveal that an exercise intensity at 100% IAT induces a more pronounced coagulation activity than exercises at 80% IAT. 100% IAT led to a significant higher increase in FVIII (80% IAT 85?±?33 to 114?±?30% vs. 100% IAT 81?±?20 to 132?±?29%) and TAT (80% IAT 2.5?±?1.4 to 2.9?±?1.0???g/l vs. 100% IAT 2.6?±?1.0 to 5.4?±?4.2???g/l). Furthermore, both exercises affected fibrinolysis, but it was significantly higher at 100% IAT (tPA activity; 80% IAT 0.44?±?0.17 to 4.65?±?2.67?U/ml vs. 100% IAT 0.43?±?0.19 to 6.47?±?3.97?U/ml). The data show that fibrinolytic activity is significantly elevated already after moderate exercise (80% IAT). After strenuous exercise (100% IAT), coagulation is more sharply enhanced together with a higher increase of fibrinolysis in comparison with 80% IAT. However, haemostasis seems to be in balance after moderate as well as after strenuous exercise intensity in healthy, untrained participants. Based on these data, exercise-induced changes of both haemostatic systems should also be tested in patients with cardiovascular diseases in order to be in a position to give recommendations for endurance training modalities in rehabilitation training.     

Day/Night Rhythm of Hemostatic Factors in Obstructive Sleep Apnea

Study Objectives:

To investigate the hypothesis that day/night patterns of prothrombotic activity differ between patients with obstructive sleep apnea (OSA) and individuals with no OSA.

Design:

Prothrombotic markers'' day/night rhythms recorded over one 24-h period.

Setting:

General clinical research center.

Patients:

38 untreated OSA patients as verified by polysomnography (apnea-hypopnea index ≥10/h sleep) and 22 non-OSA controls.

Measurements and Results:

Blood samples were collected every 2 h to measure plasma levels of fibrinolysis-inhibiting plasminogen activator inhibitor (PAI)-1 and the primary fibrin degradation product D-dimer. Day/night variation in hemostasis factors was examined using a cosinor analysis. Mesor (mean) PAI-1 over the 24-h period was higher (P = 0.015), and mesor of D-dimer was lower (P = 0.001) in patients with OSA than in the non-OSA controls. These group differences stayed significant when controlling for age and gender. After further adjustment for body mass index, mean arterial pressure, and smoking, the relationship between OSA and PAI-1 became non-significant, but the relationship between OSA and D-dimer continued to be significant (P = 0.006). In the fully adjusted analysis, the amplitude (peak) for D-dimer was lower in OSA patients than in non-OSA controls (P = 0.048). The acrophase (time of the peak) for PAI-1 and D-dimer did not significantly differ between groups.

Conclusions:

The relatively higher average level of PAI-1 and lower average level of D-dimer across the 24-h in OSA patients might reflect decreased fibrinolytic capacity and fibrin degradation, respectively. The findings provide some evidence for a prothrombotic state in OSA, but were only partially independent of metabolic variables.

Citation:

von Käanel R; Natarajan L; Ancoli-Israel S; Mills PJ; Loredo JS; Dimsdale JE. Day/night rhythm of hemostatic factors in obstructive sleep apnea. SLEEP 2010;33(3):371-377.     

Coagulation cascade and fibrinolysis in patients with multiple-drug allergy syndrome.

BACKGROUND: Previous studies have shown that patients with multiple-drug allergy syndrome (MDAS) frequently have positive autologous serum skin test results, similar to patients with chronic urticaria (CU). Recent investigations have found that patients with CU show signs of thrombin generation and activation of the tissue factor pathway of the coagulation cascade. OBJECTIVE: To study thrombin generation and fibrinolysis in patients with MDAS. METHODS: Nine patients with MDAS underwent autologous plasma skin testing (APST) and measurement of plasma prothrombin fragment F(1 + 2) and D-dimer levels. Furthermore, the basophil histamine-releasing activity of plasma from patients with MDAS was evaluated. Plasma samples from 74 healthy control subjects and 13 patients with CU were used as negative and positive controls, respectively. RESULTS: All 9 patients with MDAS had positive APST results, and 7 showed elevated plasma levels of fragment F(1 + 2). In patients with MDAS, the median F(1 + 2) level (339 pmol/L; interquartile range [IQR], 250-401 pmol/L) significantly exceeded that in healthy controls (159 pmol/L; IQR, 123-196 pmol/L) (P = .001) but did not significantly differ from that in controls with CU (292 pmol/L; IQR, 182-564 pmol/L; P = .38). Plasma D-dimer levels were normal in all the patients with MDAS and were significantly lower than in controls with CU (P = .009). Finally, the histamine-releasing activity of plasma from patients with MDAS was significantly increased and correlated with F(1+ 2) levels (r = 0.68; P = .04). CONCLUSION: Positive APST results and thrombin generation indicate a common physiopathologic background in MDAS and CU. The lower D-dimer levels suggest that fibrinolysis occurs less intensely in MDAS than in CU.     

Changes in von Willebrand factor and fibrinolysis following a post-exercise cool-down

The purpose of this study was to determine the effect of a post-exercise active cool-down on von Willebrand factor and fibrinolysis. Ten subjects performed two maximal oxygen uptake (O_2max) tests followed by a 10-min passive (PC) or an active (AC) cool-down. Blood samples were obtained pre-exercise, post-exercise, post-PC/AC, and 1 h post-exercise and analyzed for von Willebrand factor antigen (vWf:Ag), tissue plasminogen activator (tPA) antigen and activity and plasminogen activator inhibitor-1 (PAI-1) activity. Data were analyzed using repeated measures analysis of variance. No significant differences were found between O_2max tests for treadmill time, O_2max, respiratory exchange ratio, maximal heart rate, or maximal blood lactate concentration. vWf:Ag was significantly elevated (P<0.05) following PC [198.4 (18.3)% normal] versus AC [174.5 (15.6)% normal] and remained elevated 1-h post-exercise [179.4 (16.4)% normal for PC vs 158.6 (13.8)% normal for AC]. There were no differences between tests for tPA or PAI-1 activity, although tPA antigen was significantly elevated following PC versus AC (P <0.05). Following the cool-down, hematocrit was higher (P <0.05) for the PC test [48.90 (0.36)] compared with AC [47.43 (0.51)]. An AC reduces post-exercise vWf:Ag and tPA antigen without affecting tPA or PAI-1 activity.     

Severe chronic urticaria is associated with elevated plasma levels of D-dimer

Background:  Patients with chronic urticaria (CU) frequently show signs of thrombin generation as a result of the activation of the extrinsic pathway of coagulation and signs of fibrinolysis as shown by slightly increased mean D-dimer plasma levels. Here, we studied patients with severe CU to see whether the activation of coagulation and fibrinolysis parallels the severity of the disease.
Methods:  Eight consecutive patients with severe exacerbations of CU and 13 with slight CU were studied. Plasma prothrombin fragment F₁₊₂ as well as D-dimer were measured by ELISA. Serum histamine-releasing activity was assessed by basophil histamine release assay. Seventy-four normal subjects were used as controls.
Results:  In patients with severe CU, median levels of both D-dimer (11.20 nmol/l) and F₁₊₂ (592 pmol/l) largely exceeded those found in patients with slight CU [D-dimer: 2.66 nmol/l ( P  = 0.001) and F₁₊₂: 228 pmol/l ( P  = 0.003)] and in normal subjects [D-dimer: 1.41 nmol/l ( P  = 0.0001) and F₁₊₂: 159 pmol/l ( P  = 0.0001)]. Sera from 25% of patients with severe CU and 31% of those with slight CU, but from none of normal subjects, showed in vitro histamine-releasing activity. D-dimer and F₁₊₂ levels were significantly correlated each other ( r  = 0.64, P  = 0.002) and with CU severity score ( r  = 0.80–0.90, P  = 0.0001), but no correlation was observed between serum histamine-releasing activity and coagulation parameters or severity score.
Conclusions:  Severe exacerbations of CU are associated with a strong activation of coagulation cascade and fibrinolysis. Whether this activation is the cause of CU or acts as an amplification system is still a matter of debate.     

Do haemostasis activation markers that predict cardiovascular disease exist?

Recognition of the central role of thrombosis in the pathogenesis of cardiovascular disease has prompted growing interest in the association of haemostatic variables with cardiovascular disease. In investigating the predictive value of haemostasis markers, a promising type of measurement is that of the activation products of coagulation and fibrinolysis: prothrombin fragment 1+2 (F1+2), fibrinopeptide A (FPA), soluble fibrin,thrombin-antithrombin (TAT), plasmin-antiplasmin(PAP) complexes and D-dimer. D-dimer was most extensively studied and there is substantial evidence that D-dimer is a strong, consistent predictor of cardiovascular events in the general population and inpatients with cardiovascular disease. Data on other markers are considerably less abundant and more controversial. The prognostic value of these markers remains to be fully defined in future epidemiological and clinical studies.     

3-Isobutyl-1-methylxanthine (IBMX) affects potassium permeability in rat sensory neurones via pathways that are sensitive and insensitive to [Ca2+]in

The effects of externally applied 3-isobutyl-1-methylxanthine (IBMX), in millimolar concentrations, on the membrane currents in dorsal root ganglia (DRG) neurones isolated from newborn rats were investigated using the amphotericin-based perforated patch-clamp technique. In some experiments, simultaneous measurements of intracellular Ca²⁺ concentration ([Ca²⁺]_in) were performed using fura-2 microfluorimetry. Applications of IBMX induced elevation of [Ca²⁺]_in resulting from Ca²⁺ release from caffeine-ryanodine-sensitive internal stores. In addition to Ca²⁺ release, IBMX produced a biphasic membrane current response comprised of an inward current transiently interrupted by outward current. The onset of the inward current slightly preceded the onset of the [Ca²⁺]_in transient, while the interrupting outward current developed synchronously with the [Ca²⁺]_in rise. The development of IBMX-induced outward current ultimately needed the [Ca²⁺]_in elevation. After the depletion of Ca²⁺ stores by IBMX or caffeine exposure, the subsequent IBMX challenge failed to produce both the [Ca²⁺]_in transient and outward membrane current, although the inward current remained unchanged. Both components of the IBMX-induced membrane current response had a reversal potential close to the K⁺ equilibrium potential and the IBMX-induced membrane current response disappeared while dialysing the cell interior with K⁺-free, Cs⁺-containing solutions suggesting their association with K⁺ channel activity. External administration of 10 mM tetraethylammonium chloride (TEA-Cl) evoked an inward current similar to that observed in response to IBMX; in the presence of TEA-Cl, IBMX application was almost unable to induce additional inward current. IBMX (5 mM) effectively (50%) inhibited K⁺ currents evoked by step depolarizations of membrane potential. We suggest that IBMX affects membrane permeability via activation of Ca²⁺-regulated K⁺ channels and direct inhibition of TEA-sensitive K⁺ channels.     

Prothrombotic coagulation abnormalities preceding the hemolytic-uremic syndrome.

BACKGROUND: The hemolytic-uremic syndrome is a thrombotic complication of Escherichia coli O157:H7 infection. It is not known whether the coagulation abnormalities precede, and potentially cause, this disorder. METHODS: In 53 children infected with E. coli O157:H7, we measured a panel of markers indicating activation of the clotting cascade and renal function within four days after the onset of illness. These markers were measured again in as many as possible of the 16 children in whom the hemolytic-uremic syndrome developed. RESULTS: The children in whom the hemolytic-uremic syndrome subsequently developed had significantly higher median plasma concentrations of prothrombin fragment 1+2, tissue plasminogen activator (t-PA) antigen, t-PA-plasminogen-activator inhibitor type 1 (PAI-1) complex, and D-dimer than children with uncomplicated infection. These abnormalities preceded the development of azotemia and thrombocytopenia. When the hemolytic-uremic syndrome developed, the urinary concentrations of beta2-microglobulin and N-acetyl-beta-glucosaminidase rose significantly (P=0.03 for both increases); the plasma concentrations of t-PA antigen, t-PA-PAI-1 complex, D-dimer, and plasmin-antiplasmin complex also increased significantly. The concentration of t-PA antigen correlated with that of the t-PA-PAI-1 complex in a linear regression model (squared correlation coefficient, 0.80; P<0.001). CONCLUSIONS: In the hemolytic-uremic syndrome, thrombin generation (probably due to accelerated thrombogenesis) and inhibition of fibrinolysis precede renal injury and may be the cause of such injury.     

Energy cost and energy sources of a ballet dance exercise in female adolescents with different technical ability

This study evaluated energy cost and energy sources of a ballet exercise (grand adage) in young female dancers with different technical ability, and then related the energy sources to the subject’s and anaerobic threshold (IAT). Twenty-five dancers (13–16 years) were divided into two different technical ability groups: low-level (n = 13) and high-level (n = 12). The overall energy requirement of dance exercise (VO_2eq) was obtained by adding the amount of VO₂ during exercise above resting (aerobic source or VO_2ex) to the VO₂ up to the fast component of recovery (anaerobic alactic source or VO_2al) and to the energy equivalent of peak blood lactate accumulation (anaerobic lactic source or ) of recovery. VO_2eq of exercise amounted to 81 ± 10 and 94 ± 9 ml kg⁻¹ in low-level and high-level groups, respectively. VO_2ex represented the higher fraction (65 ± 4% and 77 ± 5%) in low-level and high-level groups, respectively, of VO_2eq in both the groups. In the low-level group the remaining fractions were: 23 ± 2 % for VO_2al and 12 ± 1% for . In high-level group the remaining fractions were: 18 ± 2 % for VO_2al and 4 ± 1% for . Between two groups, significant differences were found in VO_2ex (P < 0.01), (P < 0.01), and VO_2al (P < 0.05). IAT was 55 and 60% of for low-level and high-level dancers, respectively. Low-level dancers performed more exercise above IAT than high-level. For these reasons, it should be better to define exercise intensity according to the IAT parameter and not only to      

Prothrombin activation by thrombolytic agents

Previous studies showed an early increase of fibrinopeptide A and thrombin-anti-thrombin III complex (TAT) plasma levels during thrombolytic therapy. This might be caused not only by liberation of preformed thrombin from the thrombus or reperfused tissue, but also by activation of prothrombin.In 11 patients with acute myocardial infarction treated with 1.5 million U streptokinase (SK) over 30 min, and in 6 patients with deep vein thrombosis receiving standard dose urokinase (UK) infusion, TAT and the prothrombin fragment F1+2 increased significantly 3h after commencing thrombolytic therapy, and decreased again thereafter.In vitro, TAT and F1+2 levels increased in anticoagulated normal plasma after incubation with SK, UK or tissue-type plasminogen activator (t-PA). By incubation of purified prothrombin with SK+plasminogen (PLG), UK, UK+PLG, t-PA, t-PA+PLG, or plasmin, F1+2 immunoreactivity was generated. Also the generation of thrombin-like activity from purified prothrombin could be demonstrated by means of a chromogenic substrate assay with inhibition of non-specific cleavage by purified plasminogen activator inhibitor type 2 (PAI-2) or α₂-antiplasmin (APL).These results demonstrate an activation of prothrombin associated with stimulation of fibrinolysis. Further studies should clarify the clinical significance of this phenomenon, and whether it could have implications for optimizing the concomitant anticoagulation in order to prevent reocclusion in patients undergoing thrombolysis.     

Regional location of α1-antichymotrypsin and α1-antitrypsin genes on human chromosome 14

The human protease inhibitor genes ₁ antitrypsin (₁-PI) and ₁-antichymotrypsin (₁-ACT) are acute-phase proteins which are induced in response to inflammation. These inhibitors function to limit the activity of serine proteases in vivo. ₁-PI acts as an inhibitor of neutrophil elastase to protect the elastin fibers of the lung. Genetic deficiencies of ₁-PI result in development of chronic pulmonary emphysema. The physiologic role of ₁-ACT has not been clearly defined, but it also appears to function in the maintenance of protease-protease inhibitor equilibrium in the lung. Nucleic acid and protein sequence homologies detected between ₁-PI and ₁ t-ACT suggested an evolutionary relationship. Gene mapping experiments were performed to determine if these protease inhibitor genes reside at the same chromosomal locus in man. In situ hybridization data demonstrate that both ₁-PI and ₁-ACT map to the same region, q31–q32.3, on chromosome 14.