Changes in the infectivity, pyruvate kinase activity, acid phosphatase activity and P-glycoprotein expression in glibenclamide-resistant Leishmania mexicana

We previously demonstrated susceptibility of Leishmania sp. to glibenclamide, a K⁺-ATP transport blocker which interacts with members of the superfamily of adenosine 5′ triphosphate-binding cassette transporters. In order to characterize the molecular differences between a sensitive Leishmania strain, NR(Gs), and an experimentally selected glibenclamide-resistant strain, NR(Gr), specific biochemical and functional parameters have been evaluated both in the wild type and in the resistant strain. Most noteworthy, NR(Gr) exhibit an increased expression of P-glycoprotein and a decreased activity of functional key enzymes such as acid phosphatase, a prominent virulent factor of the parasite, and pyruvate kinase, a key control enzyme for both carbohydrate and protein metabolism. The specific biochemical, metabolic and functional changes observed in the resistant strain correlated with a reduced infectivity of stationary phase NR(Gr) in J774 macrophages and suggested a mechanism to overcome the effect of glibenclamide. Received: 21 January 2000 / Accepted: 1 March 2000     

Skeletal muscle monocarboxylate transporter content is not different between black and white runners

The superior performance of black African runners has been associated with lower plasma lactate concentrations at sub-maximal intensities compared to white runners. The aim was to investigate the monocarboxylate transporters 1 (MCT1) and MCT4 content in skeletal muscle of black and white runners. Although black runners exhibited lower plasma lactate concentrations after maximum exercise (8.8 ± 2.0 vs. 12.3 ± 2.7 mmol l⁻¹, P < 0.05) and a tendency to be lower at 16 km h⁻¹ (2.4 ± 0.7 vs. 3.8 ± 2.4 mmol l⁻¹, P = 0.07) than the white runners, there were no differences in MCT1 or MCT4 levels between the two groups. For black and white runners together, MCT4 content correlated significantly with 10 km personal best time (r = −0.74, P < 0.01) and peak treadmill speed (r = 0.88, P < 0.001), but MCT1 content did not. Although whole homogenate MCT content was not different between the groups, more research is required to explain the lower plasma lactate concentrations in black runners.     

萝摩甙抗自由基损伤作用的实验研究

目的:探讨萝摩甙对自由基所致脑损伤的神经元保护作用及机制。方法:复制脑缺血模型及H₂O₂诱导神经元损伤模型,分别测定大鼠脑组织、培养神经元中的丙二醛(MDA)含量以及培养神经元中的乳酸脱氢酶(LDH)漏出率、DNA断裂率和羟自由基清除率,观察萝摩甙对损伤神经元的保护作用。结果:萝摩甙可明显降低脑缺血造成的MDA的升高,亦可明显降低H₂O₂对神经元造成的LDH漏出率、DNA断裂率增加和丙二醛含量的升高,而且随着萝摩甙浓度的升高羟自由基清除率明显升高。结论:萝摩甙可通过清除自由基来保护神经元。     

The effect of physical conditioning on antipyrine clearance

The effects of physical conditioning on antipyrine clearance were studied in two groups of subjects. Healthy men not engaged in the systematic practice of any sport were compared with endurance runners (defined as men running >80 km/week). Studies were carried out at three different periods of the annual plan training at 4-month intervals. Antipyrine was administered orally and pharmacokinetic parameters were obtained from saliva samples by the multiple-sample method. Endurance performance, expressed in terms of the maximal oxygen uptake (V˙O_{2 max}), the ventilatory threshold and the 4-mM · l⁻¹ lactate threshold (OBLA), was higher in trained than in control subjects at each of the three periods. Antipyrine clearance was also significantly elevated and antipyrine half-life reduced in runners during all periods. No significant difference in V˙O_{2 max} or antipyrine clearance was found between the various periods in either trained or control subjects. Both ventilatory threshold and OBLA increased significantly along the training period in conditioned subjects. Significant correlations were found between antipyrine clearance and V˙O_{2 max}, ventilatory threshold and OBLA. In summary, these results indicate an association between aerobic conditioning and increased hepatic oxidative metabolism of low-clearance drugs. Accepted: 15 July 1997     

Luminal transport step of para-aminohippurate (PAH): transport from PAH-loaded proximal tubular cells into the tubular lumen of the rat kidney in vivo

 Proximal tubular cells were loaded for 10 s with [³H]para-aminohippurate ([³H]PAH) by microperfusing the peritubular capillaries with Ringer solution containing 0.05 mmol/l PAH. Immediately thereafter [³H]PAH influx from cells into a column of equilibrium solution injected into the oil-filled tubular lumen was measured by re-aspirating the fluid after 1–10 s of contact time. The rise of luminal PAH concentration within 2 s of contact time was almost linear, reaching a luminal / capillary concentation ratio of 1.6 after 2 s and of 3.2 after 5 s. The 2-s PAH concentration ratio was not changed when different manoeuvres were applied to depolarize proximal tubular cells. Also, the 2-s PAH concentration ratio was not influenced by varying the luminal pH from 6.0 to 8.0 or the luminal Cl^–concentration from zero to 134 mmol/l or when either 5 mmol/l urate or 25 mmol/l lactate was in the luminal perfusate. A decrease in the 2-s PAH concentration ratio, i.e. trans-inhibition, was observed when 25 or 50 mmol/l HCO₃ ^–(–50%) was in the luminal perfusate. Trans-inhibition was also seen with 5 mmol/l of the following substituted benzoates: 2-hydroxy-benzoate (–58%), 2-methoxy-benzoate (–46%), 2-hydroxy-benzoate-acetyl ester (–36%), 2-hydroxy-3,5-dinitro-benzoate (–48%), 3,5-dichloro-benzoate (–49%), and 2,3,5-trichloro-benzoate (–45%). No effect was seen with benzoate, 3-hydroxy-benzoate, 2-chloro-benzoate, 2-nitro-benzoate, 2,5-dinitro-benzoate, 3-sulfamoyl-benzoate and 4-sulfamoyl-benzoate. However, analogues of the latter two compounds possessing two additional side groups, such as furosemide and piretanide, or a hydrophobic moiety, such as probenecid, were inhibitory (by –62, –41 and –49% respectively). Phenoxyacetate had no effect; however, it inhibited if in addition it had three chloro groups, as in 2,4,5-trichlorophenoxyacetate (–71%) or a hydrophobic carbamoyl side group, as in mersalylic acid (salyrgan, –75%). Benzene-sulfonate trans-inhibited (–33%), as did phenolsulfonphthalein (phenol red, –39%) and sulfofluorescein (–55%). However, the trans-inhibitory effect of the corresponding carboxy-compounds was absent (phenolphthalein) or weaker (fluorescein, –42%). The trans-inhibitory effect of the uricosurics ethacrynic acid (–53%), tienilic acid (–55%) indacrinone (–72%) and benzbromarone (–42%) could be attributed to two chloro or bromo side groups on the benzene ring. Other trans-inhibiting uricosuric substances were indomethacin (–42%), sulfinpyrazone (–38%), losartan (–80%) its metabolite EXP 3174 (–55%), and AA 193 (–65%). These organic acids, with pKa values between 2.8 and 4.9, possess chloro and sulfin groups, as well as heterocyclic 5-ring and hydrophobic ring or chain areas. No significant effect was seen with 5 mmol/l PAH, 2-oxo-glutarate, DIDS, cGMP, prostaglandin E₂, cortisol, benzylamiloride, pyrazinoic acid and 25 mmol/l lactate. Our data indicate that in situ the secretory luminal PAH transport proceeds in a non-rheogenic fashion, per exclusionem by anion exchange. The observed trans-inhibition of PAH secretion seems to correlate with the affinity for the luminal PAH transporter and, for uricosuric substances, with their uricosuric potency. Received: 15 October 1996 / Received after revision: 17 December 1996 / Accepted: 18 December 1996     

Nitric oxide donors offer protection to RBC from storage lesion

BackgroundRed blood cell (RBC), which is the most commonly transfused blood component, due to its ability to save a life in absence of any other blood components, can be stored up to maximum 6 weeks by following standard preservation procedure. During storage, RBC undergoes various biophysical and biochemical changes (commonly known as storage lesion) for which blood transfusion with “old RBC” shows a lot of clinical problems especially relevant to critically ill patients. Recent research on S-nitrosylation of haemoglobin to improve oxygen delivery of banked blood revealed the important role of nitric oxide (NO) in protecting storage lesion.Materials and methodsIn the present study, we used various “NO donating” chemicals with different NO release dynamics and chemistries in RBC storage cocktails to test the effects of NO on storage lesion. Changes in different storage markers were evaluated after 7 days storage of pre-treated RBC.ResultsAll the NO donors have shown protection against hemolysis. However, S-nitroso glutathione (GSNO) ranks first in shielding RBCs from storage lesion and additionally, it helps in elevating the value of 2, 3-di phosphoglycerate (2, 3-DPG), improving the RBC membrane fluidity and decreasing the adhesion towards endothelial monolayer.DiscussionPresent study reveals that NO released from NO donors confers protection against storage lesions of the RBC. Further, the study confirms that pre-treatment with GSNO, a NO donor and a nitrosylating agent, ensures the best protection to RBC during low temperature storage, when compared to other NO donor treatments.     

Changes in blood lactate and respiratory gas exchange measures in sports with discontinuous load profiles

This study compares two different sport events (orienteering = OTC; tennis = TEC) with discontinuous load profiles and different activity/recovery patterns by means of blood lactate (LA), heart rate (HR), and respiratory gas exchange measures (RGME) determined via a portable respiratory system. During the TEC, 20 tennis-ranked male subjects [age: 26.0 (3.7) years; height: 181.0 (5.7) cm; weight: 73.2 (6.8) kg; maximal oxygen consumption (V˙O₂max): 57.3 (5.1) ml·kg⁻¹·min⁻¹] played ten matches of 50 min. During the OTC, 11 male members of the Austrian National Team [age: 23.5 (3.9) years; height: 183.6 (6.8) cm; weight: 72.4 (3.9) kg; V˙O₂max: 67.9 (3.8) ml·kg⁻¹·min⁻¹] performed a simulated OTC (six sections; average length: 10.090 m). In both studies data from the maximal treadmill tests (TT) were used as reference values for the comparison of energy expenditure of OTC and TEC. During TEC, the average V˙O₂ was considerably lower [29.1 (5.6) ml^·kg^−1·min⁻¹] or 51.1 (10.9)% of VO₂max and 64.8.0 (13.3)% of V˙O₂ determined at the individual anaerobic threshold (IAT) on the TT. The short high-intensity periods (activity/recovery = 1/6) did not result in higher LA levels [average LA of games: 2.07 (0.9) mmol·l⁻¹]. The highest average V˙O₂ value for a whole game was 47.8 ml·kg^−1·min⁻¹ and may provide a reference for energy demands required to sustain high-intensity periods of tennis predominately via aerobic mechanism of energy delivery. During OTC, we found an average V˙O₂ of 56.4 (4.5) ml·kg⁻¹·min⁻¹ or 83.0 (3.8)% of V˙O₂max and 94.6 (5.2)% of V˙O₂ at IAT. In contrast to TEC, LA were relatively high [5.16 (1.5) mmol·l⁻¹) although the average V˙O₂ was significantly lower than V˙O₂ at IAT. Our data suggest that portable RGEM provides valuable information concerning the energy expenditure in sports that cannot be interpreted from LA or HR measures alone. Portable RGEM systems provide valuable assessment of under- or over-estimation of requirements of sports and assist in the optimization and interpretation of training in athletes. Electronic Publication     

Negative accumulated oxygen deficit during heavy and very heavy intensity cycle ergometry in humans

The concept of the accumulated O₂ deficit (AOD) assumes that the O₂ deficit increases monotonically with increasing work rate (WR), to plateau at the maximum AOD, and is based on linear extrapolation of the relationship between measured steady-state oxygen uptake (O₂) and WR for moderate exercise. However, for high WRs, the measured O₂ increases above that expected from such linear extrapolation, reflecting the superimposition of a "slow component" on the fundamental O₂ mono-exponential kinetics. We were therefore interested in determining the effect of the O₂ slow component on the computed AOD. Ten subjects [31 (12) years] performed square-wave cycle ergometry of moderate (40%, 60%, 80% and 90% ), heavy (40%), very heavy (80%) and severe (110% O_{2 peak}) intensities for 10–15 min, where is the estimated lactate threshold and is the WR difference between and O_{2 peak}. O₂ was determined breath-by-breath. Projected "steady-state" O₂ values were determined from sub- tests. The measured O₂ exceeded the projected value after ~3 min for both heavy and very heavy intensity exercise. This led to the AOD actually becoming negative. Thus, for heavy exercise, while the AOD was positive [0.63 (0.41) l] at 5 min, it was negative by 10 min [–0.61 (1.05) l], and more so by 15 min [–1.70 (1.64) l]. For the very heavy WRs, the AOD was [0.42 (0.67) l] by 5 min and reached –2.68 (2.09) l at exhaustion. For severe exercise, however, the AOD at exhaustion was positive in each case: +1.69 (0.39) l. We therefore conclude that the assumptions underlying the computation of the AOD are invalid for heavy and very heavy cycle ergometry (at least). Physiological inferences, such as the "anaerobic work capacity", are therefore prone to misinterpretation.     

The effects of training intensity on muscle buffer capacity in females

We examined changes in muscle buffer capacity (βm_{in vitro}), and the lactate threshold (LT) after 5 weeks of high-intensity interval training (INT) above the LT or moderate-intensity continuous training (CON) just below the LT. Prior to and immediately after training, 16 female subjects performed a graded exercise test to determine and the LT, followed 2 days later by a resting muscle biopsy from the vastus lateralis muscle to determine βm_{in vitro}. Following baseline testing, the subjects were randomly placed into the INT (n=8) or CON training group (n=8). Subjects then performed 5 weeks of cycle training (3 days per week), performing either high-intensity INT (6–10×2 min at 120–140% LT with 1 min rest) or moderate-intensity CON (80–95% LT) training. Total training volume was matched between the two groups. After the training period, both groups had significant improvements in (12–14%; P<0.05) and the LT (7–10%; P<0.05), with no significant differences between groups. The INT group, however, had significantly greater improvements in βm_{in vitro} (25%; 123±5–153±7 μmol H⁺·g muscle dm⁻¹·pH⁻¹; P<0.05) than the CON group (2%; 130±12–133±7 μmol H⁺·g muscle dm⁻¹·pH⁻¹, P>0.05). Our results show that when matched for training volume, high-intensity interval training above the LT results in similar improvements in and the LT, but greater improvements in βm_{in vitro} than moderate-intensity continuous training below the LT. This suggests that training intensity is an important determinant of changes to βm_{in vitro}.