高原低氧对机体无氧代谢阈值的影响

为了探讨高原低氧对机体无氧代谢阈值(AT)的影响,本研究采用Wasserman无创性方法,分别测定了11名新兵在平原(四川淮口,海拔500m)和经空运进驻高原 (西藏错那,海拔4370m)后的第3、5、7和14天的AT。结果表明:新兵进驻高原后AT由平原的813.6±147.4kg·m/min降低到395.5±194.5 kg·m/min(P<0.01);高原低氧引起AT的降低幅度与受试者平原AT的高低呈正相关(r=0.933,P<0.01);进驻高原后第3、5、7天AT维持在较低水平,随后呈上升趋势。但移居高原1年战士的AT仍低于平原水平(P<0.05)。提示,高原低氧能够显著地降低机体的AT,并且AT越高的个体进驻高原后受低氧环境的影响程度越大。     

噪声对豚鼠内耳组织能量代谢的影响——噪声致聋机理

豚鼠暴露于125dB SPL噪声下1小时后即刻、1天内耳组织中葡萄糖(46.0±18.3μg/mg蛋白,102.2±56.3μg/mg蛋白)及丙酮酸量(30.6±8.4μg/g蛋白,47.1±15.7μg/g蛋白)均显著地高于对照组(葡萄糖26.4±8.9μg/mg蛋白,丙酮酸23.7±8.9μg/g蛋白),p<0.05。与此同时豚鼠听功能耳廓反射阈衰减dB值(30.0±12.2dB,44.8±2.5dB)显著地低于暴露前水平(49.4±2.9dB,46.2±1.9dB),P相似文献   

Direct correlation between the circadian sleep-wakefulness rhythm and time estimation in humans under social and temporal isolation

Several bodily functions in humans vary on a 24 h pattern and most of these variations persist with a circadian period ofca 25 h when subjects are studied under conditions of social and temporal isolation. We report in this paper that the estimates of short time intervals (TE) of 2 h are strongly coupled to the circadian rhythm in sleepwakefulness. There is a linear correlation between the number of hours humans stay awake (α) and their estimation of 2 h intervals. The coupling of TE to α appears to obtain only under conditions of physical well-being.     

Effect of lowered muscle temperature on the physiological response to exercise in men

The effect of low muscle temperature on the response to dynamic exercise was studied in six healthy men who performed 42 min of exercise on a cycle ergometer at an intensity of 70% of their maximal O2 uptake. Experiments were performed under control conditions, i.e. from rest at room temperature, and following 45 min standing with legs immersed in a water bath at 12 degrees C. The water bath reduced quadriceps muscle temperature (at 3 cm depth) from 36.4 (SD 0.5) degrees C to 30.5 (SD 1.7) degrees C. Following cooling, exercise heart rate was initially lower, the mean difference ranged from 13 (SD 4) beats.min-1 after 6 min of exercise, to 4 (SD 2) beats.min-1 after 24 min of exercise. Steady-state oxygen uptake was consistently higher (0.2 l.min-1). However, no difference could be discerned in the kinetics of oxygen uptake at the onset of exercise. During exercise after cooling a significantly higher peak value was found for the blood lactate concentration compared to that under control conditions. The peak values were both reached after approximately 9 min of exercise. After 42 min of exercise the blood lactate concentrations did not differ significantly, indicating a faster rate of removal during exercise after cooling. We interpreted these observations as reflecting a relatively higher level of muscle hypoxia at the onset of exercise as a consequence of a cold-induced vasoconstriction. The elevated steady-state oxygen uptake may in part have been accounted for by the energetic costs of removal of the extra lactate released into the blood consequent upon initial tissue hypoxia.     

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

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 (%VO2max) as a normalising independent variable is valid despite significant differences in the absolute VO2max of trained and untrained subjects. The subjects underwent an exercise test to exhaustion on a cycle ergometer to determine VO2max and lactate threshold. The subjects were grouped as trained (T) if their VO2max exceeded 60 ml.kg-1.min-1, and untrained (UT) if their VO2max 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% VO2max. The allocation of each exercise session (50% or 70% VO2max) 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 (0 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+], [Cl-], glucose, free fatty acid, lactate [la-], [NH3], haemoglobin [Hb] and for packed cell volume. The oxygen consumption (VO2) 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% VO2max for heart rate (fc) and venous [la-].(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of growth temperature and media composition on the fatty acid composition of Bacillus stearothermophilus AN 002

The influence of growth temperature, media composition and cell age on the chemical composition of Bacillus stearothermophilus strain AN 002 has been determined. The total cellular protein decreased and the free amino acid content increased with growth temperature, in both exponential and stationary growth phase. The protein and free amino acid contents of cells were higher in the stationary phase than in the exponential phase, irrespective of growth temperature and media composition. The RNA content was only reduced in cells grown at 55° C. No significant variations were observed in the DNA and carbohydrate contents with respect to growth temperature and cell age. The total lipid and fatty acid compositions on the other hand varied as a function of growth temperature, cell age and media composition. Differences in the relative concentrations of even, odd and branched chain fatty acids were noticed. Novariation was observed in the antiiso and unsaturated fatty acids with respect to growth temperature. The unique variations in the fatty acid composition and total lipids at the growth temperature of 50° C and their variations in the stationary growth phase seem to be characteristic for B. stearothermophilus AN 002.     

Searching behaviour and cereal aphid consumption by Bembidion lampros and Pterostichus cupreus, in relation to temperature and prey density

Maximum consumption rates were determined for two carabids, Bembidion lampros Herbst. and Pterostichus cupreus L., feeding on the cereal aphid Rhopalosiphum padi L. at different temperatures in the laboratory. Mean daily consumption increased with increasing temperature for both species, B. lampros consuming a maximum of 16 1–3 instar nymphs and 9 apterous adult aphids at 25°C. P. cupreus was particularly voracious and consumed 125 apterous adult R. padi per day at 20°C. The behaviour of both species was analysed by video filming starved beetles, maintained at different constant temperatures, in arenas sown with spring barley. The behavioural components (1) still; (2) run/walk; (3) search and (4) confrontation were identified and were common to both species. P. cupreus was more active over the temperature range tested; B. lampros was inactive under 10°C. The proportion of time spent searching, number of plants searched, and velocity increased with increasing temperature for both species. When observed in similar arenas seeded with R. padi colonies, individuals of P. cupreus significantly increased their time spent searching in arenas with increasing aphid density. Following discovery of an aphid colony, individuals climbed and searched the host plant and its nearest neighbours. Plants in aphid free arenas were rarely climbed. B. lampros was not observed climbing in either aphid free arenas or in arenas with increasing aphid densities, and did not significantly increase its time spent searching in response to increased prey density. The few B. lampros that found aphids caught them walking on the soil surface. The relative efficiences of these two carabids as predators of R. padi are discussed, and the results are compared with similar studies elsewhere with predators of Sitobion avenae on winter wheat.

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Résumé Les taux maximum de consommation de R. padi L. à différentes températures ont été déterminés au laboratoire chez deux carabes, B. lampros Herbstet P. cupreus L. La consommation moyenne a augmenté avec la température chez les deux espèces, B. lampros consommant un maximum de 15,9 larves des stades 1 à 3 et 9,1 pucerons adultes aptères, à 25°C. P. cupreus a été particulièrement vorace et a consommé 125,3 adultes aptères par jour à 20°C. Le comportement des deux espèces a été observé en filmant en vidéo des carabes à jeun, maintenus à différentes températures constantes, dans des enceintes semées en orge de printemps. Des éléments du comportement, communs aux deux espèces, ont été définis: 1) immabilité, 2) marche et course, 3) recherche, 4) affrontement. P. cupreus a été plus actif à toutes les températures, B. lamprosa été inactif au-dessous de 10°C. La part de temps consacrée à la recherche, le nombre de plantes prospectées, et la vitesse ont augmenté avec la température chez les deux espèces. Dans des enceintes similaires colonisées par R. padi, P. cupreus a significativement augmenté le temps consacré à la recherche dans les enceintes, parallèlement à l'augmentation de la densité des pucerons. Après la découverte d'une colonie de pucerons, P. cupreus escalade et prospecte la plante et ses voisines immédiates; tandis que les plantes des enceintes sans pucerons sont rarement escaladées. B. lampros n'a pas été observé escaladant des plantes d'enceintes avec ou sans pucerons, et il n'a pas accru son temps de prospection en fonction de la densité de pucerons. Les quelques B. lampros qui ont capturé des pucerons l'ont fait lorsque ceux-ci marchaient sur la surface du sol. La discussion a porté sur l'efficacité relative des deux carabes comme prédateurs de R. padi, et les résultats ont été comparés à ceux d'études du même type, menées ailleurs, avec des prédateurs de Sitobion avenae sur blé d'hiver.

     

Factors influencing nitrate depletion in a rural stream

A mass balance procedure was used to analyze rates of nitrate depletion in three adjacent reaches of West Duffin Creek, Ontario, Canada. Daily nitrate losses in individual reaches were highly variable (0.5–24 kg N) during low and moderate stream flows in May–October, 1982–1985. Nitrate removal efficiency (nitrate loss as a % of nitrate input) showed a rapid exponential decline with increased nitrate inputs to each reach. Nitrate losses and nitrate removal efficiency also had a significant negative correlation with stream discharge. The association of large nitrate loads with high stream discharge reduced the nitrate removal capacity of the stream because of shorter residence times and a higher ratio of water volume to stream bed area. Water temperature exhibited a significant positive correlation with nitrate loss which may reflect increased denitrification at higher temperatures.Variations in nitrate losses and nitrate removal efficiency between the three reaches were highly influenced by differences in water residence time. Standarized nitrate losses with respect to water residence time revealed a longitudinal decline in nitrate depletion between the reaches which was associated with a downstream decrease in stream nitrate concentration and in the organic carbon content of fine textured sediments from pool habitats.     

Temperature and the biology and predation of Ilione albiseta (Diptera: Sciomyzidae) — Potential biological control agent of liver fluke

The effect of temperature on predation by Ilione albiseta (Diptera: Sciomyzidae) on Lymnaea peregra was investigated at 14°, 17°, 20°, 23° and 26°C. The mean dry weight of snail tissue (Lymnaea peregra) attacked and consumed per day by first and second instar I. albiseta larvae was highest at 20°C while for third instar and total larval duration period it was greatest at 23°C. The mean number of snails killed per day during the third instar was also highest at 23°C. The total amount of snail tissue consumed by I. albiseta larvae increased significantly from first to second instar and from second to third instar at each constant temperature. Mean survival period of unfed first instar larvae decreased from 28.4 days at 14°C to 11 days at 26°C and the mean length of the second instar cephalopharyngeal skeleton decreased with increasing temperatures. As temperature increased the rate of consumption of oxygen (dissolved in water) by first and third instar larvae rose.