Muscle metabolism during prolonged physical exercise in dogs

In order to provide reference data, adenine nucleotide, creatine phosphate, glycogen, glycolytic intermediates and lactate muscle contents were measured in 49 dogs under resting conditions and during prolonged physical exercise of moderate intensity performed until exhaustion. Both the resting and exercise values of the measured variables were remarkably similar to those described in human subjects, except muscle lactate content which achieved higher values during submaximal exercise in dogs than in men.     

Drought stress during soybean seed filling affects storage compounds through regulation of lipid and protein metabolism

Soybean seeds have high lipid and protein contents. Adverse environmental conditions restrict seed yield and quality. We examined the changes in storage compounds caused by drought stress from R5 stage (beginning seed growth stage). Under drought stress, contents of lipid in seed were remarkably low compared to control at 24 and 29 days after treatment. Protein contents in seed were immediately decreased after water deficit treatment. On the other hand, soluble sugar contents in seed were increased by drought stress. Drought stress decreased the expression of genes involved in lipid biosynthesis (PK, BCCP2, and KAS1) and increased the genes expression involved in lipid degradation (ACX2, MS, and PEPCK). These results suggest that the increasing of sugar content in seed under drought stress was complemented by degradation of lipids. The expressions of genes encoding storage protein (Gy4 and β-conglycinin) were also decreased by drought stress. This study showed how drought stress during seed filling affects seed quality, especially lipid and protein contents, that may facilitate further research on seed storage compounds metabolism under environmental stresses.     

Amino Acid and protein metabolism in bermuda grass during water stress

The ability of Arizona Common and Coastal Bermuda grass [Cynodon dactylon (L.) Pers.] to synthesize amino acids and proteins during water stress was investigated. Amino acids were continually synthesized during the water stress treatments, but protein synthesis was inhibited and protein levels decreased.     

Photosynthesis and starch metabolism of chloroplasts during prolonged illumination

Summary The starch metabolism of the chloroplasts in the leaves of Stellaria media was studied by means of electron microscopy. During the night the starch grains diminished in size but did not disappear entirely. In the light they grew due to photosynthesis. After prolonged illumination of the plant the grains almost filled up the chloroplasts. However, after an illumination of 26–27 hr a sudded disintegration took place. This was apparently caused by the increased activity of -amylase observed in an earlier investigation to occur at this time in the chloroplasts. After the disintegration the starch grains of the chloroplasts showed irregular changes.The rate of photosynthesis and respiration was measured by an infra-red gas analyser. During prolonged illumination Stellaria media showed a rather intensive and constant rate of assimilation. The role of starch disintegration and -amylase synthesis in making possible this constant assimilation has been discussed.     

Metabolic effects of testosterone during prolonged physical exercise and fasting

Previous studies have shown a decrease in plasma testosterone during prolonged physical exercise and 72 h fasting in rats. To determine whether this hormonal change has an influence upon energy metabolism, two experiments were carried out, in which the plasma levels of testosterone were elevated during prolonged physical exercise and fasting in male wistar rats. The effects of acute and chronic increases in the levels of circulating testosterone were studied, on the one hand after human chorionic gonadotropin (H.C.G.) injection, and on the other by prolonged testosterone perfusion with an osmotic minipump. Blood and tissue sampling were performed to evaluate blood glucose, alanine, and lactate, and tissue glycogen. The results in fed and rest control rats showed no changes in blood parameters under the effect of hypertestosteronemia but there was an increase in muscle glycogen after testosterone perfusion. In 72 h fasted rats both types of hypertestosteronemia were associated with a decrease in blood alanine and lactate ranging from 25% to 35%. Only testosterone perfusion was associated with higher concentrations of muscle glycogen. After 7 h of treadmill running, testosterone perfusion and H.C.G. injection induced a 35% decrease in blood alanine and a slight decrease in blood glucose, with no change in other parameters. Whereas an elevation in the level of testosterone can induce muscle glycogen compensation in the fed resting state, it cannot counteract the exhaustion of muscle glycogen during running.     

Neuromuscular regulation and metabolism during exercise

This article reviews current evidence regarding neuromuscular regulation and metabolism during exercise. Particular emphases are given on the relationship between motor unit (MU) activity, including single MU analysis results and spinal alpha-motoneuron excitability, and cardio-respiratory response and blood lactate during dynamic exercise. In addition, a close physiological link between muscle energy metabolism and excitation-contraction processes (failure of one will affect the extent of the other) is summarized in the light of recent nuclear magnetic resonance (NMR) studies and results of neuromuscular disorder patients.     

Carnitine metabolism during prolonged exercise and recovery in humans

Lennon et al. (J. Appl. Physiol. 55: 489-495, 1983) have recently reported a large loss of muscle total carnitine (TC) after 40 min of moderate exercise. These authors have also suggested that elevations in plasma esterified carnitine (EC) were due to the release of these carnitine esters from muscle during exercise. After 10 male subjects underwent 90 min of cycle egometry we found no alteration in muscle TC from preexercise values. Plasma EC progressively increased above resting values during exercise and remained elevated above rest at 0.75 and 1.5 h into recovery. Elevations of plasma EC were largely due to a decrement in free carnitine (FC) in both conditions. Immediately postexercise the urinary fractional reabsorbsion of EC and FC were similar to that at rest. These results suggest that a net loss of TC from exercising muscle does not occur. As in other conditions marked by falling insulin concentrations, elevations in plasma EC could result from an exchange of carnitine with the hepatic carnitine pool.     

Self-cytoprotection against stress: feedback regulation of heme-dependent metabolism

This minireview provides insight into feedback regulation of heme-dependent metabolism as a defensive cellular response against stress. Interactions among heme-, iron-, porphyrin-, and CO/NO-dependent metabolic pathways during the stress-induced response are emphasized in the context of feedback regulation. The hypothetical model of the latter interactions is presented as tightly controlled feedback cycles.     

应激对同型半胱氨酸代谢的负性调节

基于应激对高同型半胱氨酸血症具有诱导作用,本文探索了应激致同型半胱氨酸(homocysteine,HCY)代谢变化的关键环节,并初步揭示了该作用的意义。以束缚应激法建立大鼠应激模型,采用高压液相-荧光检测法测定血浆HCY水平,用放射性酶学法检测不同组织中胱硫醚β合成酶(cystathionine beta-synthase,CBS)活性的变化,以及RT-PCR法和Northern blot法检测CBS mRNA水平的变化。结果可见,束缚应激可导致大鼠高同型半胱氨酸血症的发生;CBS在肝脏具有最强的代谢活性,肾脏其次,而心脏和血液中活性极低;应激大鼠肝脏CBS活性和mRNA水平均显著降低(P<0.05),应激3周时分别为对照组的70.6％±5.9％和55.9％±4.3％。以上研究结果表明,应激对HCY转硫代谢途径存在负性调节作用,其对肝脏CBS基因转录水平的调控是应激所致高同型半胱氨酸血症发生的重要诱因;肝脏是应激对HCY代谢调节的主要场所。