Glucose-6-phosphate dehydrogenase activity in monolayer cultures of thyroid epithelial cells: TSH and inhibition of nitrogen oxide synthase affect the enzyme activity and the oxygen sensitivity of the histochemical assay

The objective was to investigate glucose-6-phosphate dehydrogenase (G6PD) activity in monolayer cultures of thyroid epithelial cells and to examine whether inhibition of nitric oxide synthase affects activity of G6PD or oxygen sensitivity of the assay. Primary cultures without TSH addition prior to experiments demonstrated a TSH-dependent increase in G6PD activity. G6PD activity was higher in F12 medium than in a serum-free physiological medium. Secondary cultures grown in F12 medium demonstrated a diminished activity of G6PD and a lack of response to TSH. In the serum-free physiological medium, G6PD activity was comparable to that found in primary cultures and a response to high concentrations of TSH was maintained. In primary cultures grown in F12 medium devoid of TSH, G6PD activity decreased dose-dependently when nitric oxide synthase activity was inhibited. The oxygen sensitivity of the assay was comparable to that reported previously in malignant cells and correlated with the activity of G6PD in primary cultures. We suggest that thyroid epithelial cells may be an appropriate system to investigate oxygen sensitivity of the G6PD assay as the cells demonstrate a reduced oxygen sensitivity which can be influenced by culture conditions.     

阿霉素性心肌病之心肌线粒体酶的细胞化学研究

阿霉素性心肌病之心肌线粒体SDH和CCO的细胞化学观察发现,多数线粒体的酶活性较弱,少数较强或中等,并与ADR的累积用量和心肌损伤程度有关。作者认为SDH和CCO活性降低,线粒体能量代谢障碍在ADR引起心肌病的过程中起着重要作用。     

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.     

Characterization of the osmotic-stress response inSaccharomyces cerevisiae: osmotic stress and glucose repression regulate glycerol-3-phosphate dehydrogenase independently

Micro-organisms have developed systems to adapt to sudden changes in the environment. Here we describe the response of the yeastSaccharomyces cerevisiae to osmotic stress. A drop in the water activity (a_w) of the medium following the addition of NaCl led to an immediate shrinkage of the cells. During the 2 h following the osmotic shock the cells partially restored their cell volume. This process depended on active protein synthesis. During the recovery period the cells accumulated glycerol intracellularly as a compatible solute and very little glycerol was leaking out of the cell. We have investigated in more detail the enzymes of glycerol metabolism and found that only the cytoplasmic glycerol-3-phosphate dehydrogenase was strongly induced. The level of induction was dependent on the yeast strain used and the degree of osmotic stress. The synthesis of cytoplasmic glycerol-3-phosphate dehydrogenase is also regulated by glucose repression. Using mutants defective in glucose repression (hxk2), or derepression (snf1), and with invertase as a marker enzyme, we show that glucose repression and the osmotic-stress response system regulate glycerol-3-phosphate dehydrogenase synthesis independently. We infer that specific control mechanisms sense the osmotic situation of the cell and induce responses such as the production and retention of glycerol.     

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.     

Post-exercise ketosis and the glycogen content of liver and muscle in rats on a high carbohydrate diet

Summary Post-exercise ketosis is known to be suppressed by physical training and by a high carbohydrate diet. As a result it has often been presumed, but not proven, that the development of post-exercise ketosis is closely related to the glycogen content of the liver. We therefore studied the effect of 1 h of treadmill running on the blood 3-hydroxybutyrate and liver and muscle glycogen concentrations of carbohydrate-loaded trained (n=72) and untrained rats (n=72). Resting liver and muscle glycogen levels were 25%–30% higher in the trained than in the untrained animals. The resting 3-hydroxybutyrate concentrations of both groups of rats were very low: <0.08 mmol·1⁻¹. Exercise did not significantly influence the blood 3-hydroxybutyrate concentrations of trained rats, but caused a marked post-exercise ketosis (1.40±0.40 mmol·1⁻¹ 1 h after exercise) in the untrained animals, the time-course of which was the approximate inverse of the changes in liver glycogen concentration. Interpreting the results in the light of similar data obtained after a normal and low carbohydrate diet it has been concluded that trained animals probably owe their relative resistance to post-exercise ketosis to their higher liver glycogen concentrations as well as to greater peripheral stores of mobilizable carbohydrate.     

The cloning and sequencing of thealcB gene,coding for alcohol dehydrogenase II,inAspergillus nidulans

Alcohol dehydrogenase II (ADH II, structural genealcB) was purified from a strain H1035,biA1; alcE1; alc500 alcD1, which produces 100-times more ADH II activity than thealcAalcR deletion strain (alc500). Antibodies were raised against this ADH, and were used to screen a cDNA library in gt11. We have isolated the gene for an ADH which is over-expressed in H1035, and which we believe to be thealcB gene; cDNA and genomic clones were sequenced. The sequence contains three introns and encodes a protein of 367 amino acids. This protein shows a clear level of identity to a range of alcohol dehydrogenases, but is no more closely related to the ADH I and ADH III previously described inA. nidulans than to the ADHs ofS. pombe andS. cerevisiae. The significance of consensus sequences found in the 5 region of the gene is discussed in relation to the regulation of the gene.     

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.     

Energetics of karate kumite

It is speculated that anaerobic metabolism is the predominant source of energy in karate kumite. However, no experimental proof is currently available. The metabolic cost and fractions of aerobic and anaerobic energy of karate kumite fighting were investigated. Ten male nationally or internationally ranked karateka [means (SD) age 26.9 (3.8) years, height 1.80 (0.08) m, mass 77.2 (12.8) kg] performed two to four fights scheduled and judged like a championship. Oxygen uptake was measured continuously with a portable spirometric device. Blood lactate was determined immediately before, and minute by minute after, each fight. Aerobic, anaerobic alactic and anaerobic lactic energy were calculated from oxygen uptake during the fight (VO₂), the fast component of the post-fight oxygen uptake (VO_2PCr) above resting values and changes in blood lactate concentration (Net-BLC), respectively. Altogether, 36 fights lasting 267 (61) s were analysed. The referees decisions caused an activity-to-break ratio of approximately 2:1. VO₂, VO_2PCr, and Net-BLC per fight were 165.3 (52.4) ml^.kg^–1, 32.2 (7.2) ml^.kg^–1and 4.2 (1.9) mmol^.l^–1; the overall energy cost above rest was 334.3 (86.3) kJ per fight. Fractions of aerobic, anaerobic alactic, and lactic energy sources were 77.8 (5.8)%, 16.0 (4.6)%, and 6.2 (2.4)%, respectively. The results indicate a high metabolic rate in karate kumite. However, the acyclic activity profile implies that aerobic metabolism is the predominant source of energy and there is anaerobic supplementation, mainly by high-energy phosphates.