Lactate dehydrogenase activity and isoform distribution in normal and hypertrophic smooth muscle tissue from the rat

The lactate dehydrogenase (LDH) activity and isoform distribution of LDH were investigated in tissue samples from the rat portal vein, aorta and urinary bladder. In addition, samples were obtained from hypertrophic urinary bladder. The total LDH activity per unit smooth muscle volume was higher in the urinary bladder compared to that in portal vein and aorta. Five LDH isoforms, reflecting different combinations of the two polypeptide chains denoted H and M, could be separated by agarose gel electrophoresis. The aorta contained more of the H form compared to the portal vein and urinary bladder. This difference suggests that the aorta, which is a slow smooth muscle, is more adapted for aerobic metabolism than the faster muscles of portal vein and urinary bladder. In the hypertrophic urinary bladder a shift in LDH isoform pattern towards less of the H form was found, which correlates with a better maintenance of contraction in anoxia in this type of hypertrophic smooth muscle.     

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。     

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     

Effects of prolonged cycle ergometer exercise on maximal muscle power and oxygen uptake in humans

Summary The mechanical power (W_tot, W·kg^–1) developed during ten revolutions of all-out periods of cycle ergometer exercise (4–9 s) was measured every 5–6 min in six subjects from rest or from a baseline of constant aerobic exercise [50%–80% of maximal oxygen uptake (VO_2max)] of 20–40 min duration. The oxygen uptake [VO₂ (W·kg^–1, 1 ml O₂ = 20.9 J)] and venous blood lactate concentration ([la]_b, mM) were also measured every 15 s and 2 min, respectively. During the first all-out period, W_tot decreased linearly with the intensity of the priming exercise (W_tot = 11.9–0.25·VO₂). After the first all-out period (i greater than 5–6 min), and if the exercise intensity was less than 60% VO_2max, W_tot, VO₂ and [la]_b remained constant until the end of the exercise. For exercise intensities greater than 60% VO_2max, VO₂ and [la]_b showed continuous upward drifts and W_tot continued decreasing. Under these conditions, the rate of decrease of W_tot was linearly related to the rate of increase of V [(d W_tot/dt) (W·kg^–1·s^–1) = 5.0·10^–5 –0.20·(d VO₂/dt) (W·kg^–1·s^–1)] and this was linearly related to the rate of increase of [la]_b [(d VO₂/dt) (W·kg^–1·s^–1) = 2.310^–4 + 5.910^–5·(d [la]_b/dt) (mM·s^–1)]. These findings would suggest that the decrease of W_tot during the first all-out period was due to the decay of phosphocreatine concentration in the exercising muscles occurring at the onset of exercise and the slow drifts of VO₂ (upwards) and of W_tot (downwards) during intense exercise at constant W_tot could be attributed to the continuous accumulation of lactate in the blood (and in the working muscles).     

急性鸭乙型肝炎病毒感染病毒清除机理研究

目的 :进一步阐明嗜肝病毒自然感染过程中病毒清除机理。方法 :7只 2～ 3月龄成年重庆麻鸭静脉接种 10～ 2 0mlDHBV阳性血清 (5× 10 8～ 1× 10 9genome) ,接种后每周采血检测外周血中DHBVDNA、DHBsAg和特异抗体的产生 ;感染后第10、35天分离外周血单个核细胞用于抗原特异细胞增殖实验 ;第 5、30、6 0天取肝组织标本进行DHBVDNASouthern杂交、DHB sAg免疫组化及肝组织病理检测。结果 :DHBV感染成年鸭在 1～ 2w潜伏期后出现急性、一过性感染 ,感染高峰期肝内存在多拷贝的DHBV所有复制中间体形式 ,包括cccDNA。进一步分析显示病毒血症的消失是在快速抗原特异细胞增殖反应和高滴度特异抗体产生之后 ;与此同时 ,整个急性感染期间 ,肝细胞并无明显的损害。结论 :非细胞直接损伤机制在嗜肝病毒清除过程中发挥了重要作用。     

Effect of endurance and sprint exercise on the sensitivity of glucose metabolism to insulin in the epitrochlearis muscle of sedentary and trained rats

Summary The effects of two types of acute exercise (1 h treadmill running at 20 m· min^–1, or 6 × 10-s periods at 43 m · min^–1, 0° inclination), as well as two training regimes (endurance and sprint) on the sensitivity of epitrochlearis muscle [fast twitch (FT) fibres] to insulin were measured in vitro in rats. The hormone concentration in the incubation medium producing the half maximal stimulation of lactate (la) production and glycogen synthesis was determined and used as an index of the muscle insulin sensitivity. A single period of moderate endurance as well as the sprint-type exercise increased the sensitivity of la production to insulin although the rate of la production enhanced markedly only after sprint exercise at 10 and 100 U· ml^–1 of insulin. These effects persisted for up to 2 h after the termination of exercise. Both types of exercise significantly decreased the muscle glycogen content, causing a moderate enhancement in the insulin-stimulated rates of glycogen synthesis in vitro for up to 2 h after exercise. However, a significant increase in the sensitivity of this process to insulin was found only in the muscle removed 0.25 h after the sprint effort. Training of the sprint and endurance types increased insulin-stimulated rates of glycolysis 24 h after the last period of exercise. The sensitivity of this process to insulin was also increased at this instant. Both types of training increased the basal and maximal rates of glycogen snythesis, as well as the sensitivity of this process to insulin at the 24^th following the last training session. It was concluded that in the epitrochlearis muscle, containing mainly FT fibres, both moderate and intensive exercise (acute and repeated) were effective in increasing sensitivity of glucose utilization to insulin. Thus, the response in this muscle type to increased physical activity differs from that reported previously in the soleus muscle, representing the slow-twitch, oxidative fibres in which sprint exercise did not produce any changes in the muscle insulin sensitivity.     

The significance of an increased RQ after sucrose ingestion during prolonged aerobic exercise

Summary Four well-trained male subjects worked for periods of 6 h on bicycle ergometers at work loads requiring about 47% of their maximal aerobic capacity. In one series of studies they received only water; in a second series they received 100 g of sucrose containing 100 c U-C¹⁴-labelled sucrose at the beginning of the fourth hour of work. In a third series of experiments, the same subjects received 100 g of non-labelled sucrose at the beginning of the fourth hour. During the experiment without U-C¹⁴-labelled sucrose, blood samples were withdrawn and analysed for glucose, lactate and pyruvate content. Data from C¹⁴O₂ recovery in expired air showed a good correlation with the amount of carbohydrate oxidized during the sucrose experiment. Peak values for the respiratory exchange ratio showed the same time response as those observed for the C¹⁴O₂ in the expired air. It is concluded that the observed rise in RQ after sucrose ingestion, under the conditions studied, is of metabolic origin, resulting from a complete conversion of pyruvate to CO₂.     

Proximal tubular function in adult rats treated neonatally with enalapril

Neonatal treatment with angiotensin-converting enzyme (ACE) inhibitors or the angiotensin II type-1 receptor antagonist losartan in rats induces irreversible renal histological abnormalities, mainly papillary atrophy, in association with an impairment in urinary concentrating ability. The aim of the present study was to assess proximal tubular function in adult rats treated neonatally with enalapril. Male Wistar rats received daily, intraperitoneal injections of either enalapril (10 mg kg^?1) or isotonic saline vehicle from 3 to 24 days of age. In 15-week-old, hydropenic rats we analysed: (i) proximal tubular iso-osmotic fluid reabsorption using the method of lithium clearance; and (ii) maximal tubular D -glucose reabsorption (Tm_G), under pentobarbital anaesthesia. The main findings were that neonatally enalapril-treated rats showed: (i) reductions in absolute (APRH₂O) and fractional (FPRH₂O) iso-osmotic fluid reabsorption in the proximal tubules (APRH₂O: 0.50 ± 0.02 vs. 0.64 ± 0.03 mL min^?1 g KW^?1, P < 0.05; FPRH₂O: 58 ± 3 vs. 68 ± 2%, P < 0.05); and (ii) a normal Tm_G. In addition, during baseline clearance measurements neonatally enalapril-treated rats showed increases in urine volume and fractional excretion rates of sodium and potassium, a reduction in urine osmolality, whereas glomerular filtration rate and effective renal plasma flow were unaltered. These results suggest that neonatal ACE inhibition produces an irreversible, but differentiated, abnormality in proximal tubular function. Thus, the development of a normal proximal tubular function in the rat seems to be dependent on an intact renin-angiotensin system, (RAS) neonatally.     

Effects of prolonged exercise at a similar percentage of maximal oxygen consumption in trained and untrained subjects

Summary Six trained male cyclists and six untrained but physically active men participated in this study to test the hypothesis that the use of percentage maximal oxygen consumption (% , as a normalising independent variable is valid despite significant differences in the absolute of trained and untrained subjects. The subjects underwent an exercise test to exhaustion on a cycle ergometer to determine and lactate threshold. The subjects were grouped as trained (T) if their exceeded 60 ml ·kg^–1 ·min^–1, and untrained (UT) if their was less than 50 ml · kg^–1 · min-^–1. The subjects were required to exercise on the ergometer for up to 40 min at power outputs that corresponded to approximately 50% and 70% The allocation of each exercise session (50% or 70% was random and each session was separated by at least 5 days. During these tests venous blood was taken 10 min before exercise (–10 min), just prior to the commencement of exercise (–10 min), after 20 min of exercise (20 min), at the end of exercise and 10 min postexercise (+ 10 min) and analysed for concentrations of cortisol, [Na⁺], [K⁺], [CI^–], glucose, free fatty acid, lactate [la-], [NH₃], haemoglobin [Hb] and for packed cell volume. The oxygen consumption ( ) and related variables were measured at two time intervals (14–15 and 34–35 min) during the prolonged exercise tests. Rectal temperature was measured throughout both exercise sessions. There was a significant interaction effect between the level of training and exercise time at 50% for heart rate ( _c:) and venous [la^–]. At 70% and ventilation ( ) for the T group and and carbon dioxide production for the UT group increased significantly with time and there was a significant interaction effect forf _c, ]Ia^–1], [Hb] and [NH₃]. The change in body mass at 50% and 70% was significantly greater in the T group. The present study found that when two groups of male subjects with different absolute exercised at a similar percentage of some effector responses were significantly different, questioning the validity of selecting % as a normalising independent variable.