Effect of sodium citrate on performance and metabolism of human skeletal muscle during supramaximal cycling exercise

The aim of this study was to examine whether the alkalosis-induced improvement in supramaximal performance could be explained by a less-altered muscle metabolic status. Eight subjects first performed exhausting exercise at 120% peak oxygen uptake after ingesting either a placebo (PLC) or sodium citrate (CIT) at a dose of 0.5 g · kg⁻¹ body mass to determine exhaustion time (t _exh). They then, performed exercise (Lim-EX) at the same relative intensity lasting PLCt _exh minus 20 s in both treatments. Samples were taken from vastus lateralis muscle at rest (90-min after the ingestion) and at the end of Lim-EX. Arterial blood samples were obtained at rest (immediately prior to and 90 min after ingesting the drug) and during the 20-min post-exercise recovery. The t _exh was significantly increased by CIT [PLC 258 (SD 29) s, CIT 297 (SD 45) s]. The CIT raised the rest [citrate] in blood [PLC 0.11 (SD 0.01) mmol · l⁻¹, CIT 0.34 (SD 0.07) mmol · l⁻¹] and in muscle [PLC 0.78 (SD 0.23) mmol · kg⁻¹ dry mass, CIT 1.00 (SD 0.21) mmol · kg⁻¹ dry mass]. Resting muscle pH and buffering capacity were unchanged by CIT. The same fall in muscle pH was observed during Lim-EX in the two conditions. This was associated with similar variations in both the cardio-respiratory response and muscle energy and metabolism status in spite of a better blood acid-base status after CIT. Thus, CIT would not seem to allow the alkalinization of the muscle cytosolic compartment. Though sodium citrate works in a similar way to NaHCO₃ on plasma alkalinization and exercise performance, the exact nature of the mechanisms involved in the delay of exhaustion could be different and remains to be elucidated. Accepted: 26 November 1996     

Effects of NaHCO3 loading on acid-base balance, lactate concentration, and performance in racing greyhounds

This investigation examined the effects ofNaHCO₃ loading on lactateconcentration ([La]), acid-base balance, and performance for a 603.5-m sprint task. Ten greyhounds completed aNaHCO₃ (300 mg/kg body weight) andcontrol trial in a crossover design. Results are expressed as means ± SE. Presprint differences (P < 0.05) were found for NaHCO₃ vs.control, respectively, for blood pH (7.47 ± 0.01 vs. 7.42 ± 0.01), HCO₃ (28.4 ± 0.4 vs. 23.5 ± 0.3 meq/l), and base excess (5.0 ± 0.3 vs. 0.2 ± 0.3 meq/l). Peak blood [La] increased(P < 0.05) inNaHCO₃ vs. control (20.4 ± 1.6 vs. 16.9 ± 1.3 mM, respectively). Relative to control,NaHCO₃ produced a greater(P < 0.05) reduction in blood baseexcess (18.5 ± 1.4 vs. 14.1 ± 0.8 meq/l) andHCO₃ (17.4 ± 1.2 vs.12.8 ± 0.7 meq/l) from presprint to postexercise. Postexercise peak muscle H⁺concentration ([H⁺])was higher (P < 0.05) inNaHCO₃ vs. control (158.8 ± 8.8 vs. 137.0 ± 5.3 nM, respectively). Muscle[H⁺] recoveryhalf-time (7.2 ± 1.6 vs. 11.3 ± 1.6 min) and time to predosevalues (22.2 ± 2.4 vs. 32.9 ± 4.0 min) were reduced(P < 0.05) inNaHCO₃ vs. control, respectively.No differences were found in blood[H⁺] or blood[La] recovery curves or performance times.NaHCO₃ increased postexerciseblood [La] but did not reduce the muscle or blood acid-basedisturbance associated with a 603.5-m sprint or significantly affectperformance.

     

The Influence of Bicuculline-Induced Seizures on Free Fatty Acid Concentrations in Cerebral Cortex, Hippocampus, and Cerebellum

Abstract: Using ventilated rats maintained on N₂O-O₂ (70:30, vol/vol) we induced continuous seizures with i.v. bicuculline and analysed free fatty acids (FFA) in cerebral cortex, hippocampus, and cerebellum after seizure durations of 1–120 min. In the cerebral cortex, peak FFA concentrations were observed after 5 min, with a threefold increase in total FFA content. The values then remained unchanged for the next 15-20 min, but decreased thereafter. At 60 and 120 min, total FFA contents were only moderately increased above control. In the initial period, arachidonic acid increased about 10-fold and stearic acid 2- to 3-fold, with little change in palmitic acid and linoleic acid concentrations. At all times, the docosahexenoic acid concentration was markedly increased. Following its massive accumulation at 1 min, arachidonic acid gradually decreased in concentration. Pretreatment of animals with indomethacin did not alter this behaviour. After 20 and 120 min of seizure activity, changes in total and individual FFA concentrations in the hippocampus were similar to those observed in the cerebral cortex. The cerebellum behaved differently. Thus, at 20 min the only significant change was a 5- to 10-fold increase in arachidonic acid concentration and, after 120 min, total and individual FFA concentrations were similar to control values. Furthermore, since the control values for arachidonic acid were much lower in the cerebellum, the 20-min values were only about 20% of those observed in the cerebral cortex and the hippocampus.     

Flash dietary methionine supply over growth requirements in pigs: Multi-facetted effects on skeletal muscle metabolism

Dietary methionine affects protein metabolism, lean gain and growth performance and acts in the control of oxidative stress. When supplied in large excess relative to growth requirements in diets for pigs, positive effects on pork quality traits have been recently reported. This study aimed to decipher the molecular and biochemical mechanisms affected by a dietary methionine supply above growth requirements in the loin muscle of finishing pigs. During the last 14 days before slaughter, crossbred female pigs (n = 15 pigs/diet) were fed a diet supplemented with hydroxy-methionine (Met5; 1.1% of methionine) or not (CONT, 0.22% of methionine). Blood was sampled at slaughter to assess key metabolites. At the same time, free amino acid concentrations and expression or activity levels of genes involved in protein or energy metabolism were measured in the longissimus lumborum muscle (LM). The Met5 pigs exhibited a greater activity of creatine kinase in plasma when compared with CONT pigs. The concentrations of free methionine, alpha-aminobutyric acid, anserine, 3-methyl-histidine, lysine, and proline were greater in the LM of Met5 pigs than in CONT pigs. Expression levels of genes involved in protein synthesis, protein breakdown or autophagy were only scarcely affected by the diet. Among ubiquitin ligases, MURF1, a gene known to target creatine kinase and muscle contractile proteins, and OTUD1 coding for a deubiquitinase protease, were up-regulated in the LM of Met5 pigs. A lower activity of citrate synthase, a reduced expression level of ME1 acting in lipogenesis but a higher expression of PPARD regulating energy metabolism, were also observed in the LM of Met5 pigs compared with CONT pigs. Principal component analysis revealed that expression levels of many studied genes involved in protein and energy metabolism were correlated with meat quality traits across dietary treatments, suggesting that subtle modifications in expression of those genes had cumulative effects on the regulation of processes leading to the muscle transformation into meat. In conclusion, dietary methionine supplementation beyond nutritional requirements in pigs during the last days before slaughter modified the free amino acid profile in muscle and its redox capacities, and slightly affected molecular pathways related to protein breakdown and energy metabolism. These modifications were associated with benefits on pork quality traits.     

The effect of a free radical scavenger and platelet-activating factor antagonist on FFA accumulation in post-ischemic canine brain

The effects of the platelet-activating factor antagonist BN 50739 and a free radical scavenger dimethyl sulfoxide on the accumulation of free fatty acids in post-ischemic canine brain are reported. Following 14 min of complete normothermic ischemia and 60 min of reperfusion, the total brain FFAs were approximately 150% higher than in the control group (p<0.05). Perfusion with the platelet-activating factor antagonist BN50739 in its diluent dimethyl sulfoxide during 60 min of post-ischemic reoxygenation resulted in a 61.8% (p<0.01) reduction in the total brain free fatty acid accumulation. Palmitic, stearic, oleic, linoleic, and arachidonic acids decreased by 53.8%, 63.5%, 69.0%, 47.4%, and 57.2%, respectively. Although dimethyl sulfoxide alone caused stearic and arachidonic acids to return to the normal concentration range, BN 50739 had a significant influence on recovery of palmitic, oleic, and linoleic acids and was previously shown to provide significant therapeutic protection against damage to brain mitochondria following an ischemic episode. Because free fatty acid accumulation is one of the early phenomena in cerebral ischemia, this study provides evidence to support the hypothesis that both platelet-activating factor and free radicals are involved in initiating cerebral ischemic injury.     

The effect of a low-carbohydrate diet on performance, hormonal and metabolic responses to a 30-s bout of supramaximal exercise

The aim of this study was to find out whether a low-carbohydrate diet (L-CHO) affects: (1) the capacity for all-out anaerobic exercise, and (2) hormonal and metabolic responses to this type of exercise. To this purpose, eight healthy subjects underwent a 30-s bicycle Wingate test preceded by either 3 days of a controlled mixed diet (130 kJ/kg of body mass daily, 50% carbohydrate, 30% fat, 20% protein) or 3 days of an isoenergetic L-CHO diet (up to 5% carbohydrate, 50% fat, 45% protein) in a randomized order. Before and during 1 h after the exercise venous blood samples were taken for measurement of blood lactate (LA), β-hydroxybutyrate (β-HB), glucose, adrenaline (A), noradrenaline (NA) and insulin levels. Oxygen consumption (V˙O₂) was also determined. It was found that the L-CHO diet diminished the mean power output during the 30-s exercise bout [533 (7) W vs 581 (7) W, P < 0.05] without changing the maximal power attained during the first or second 5-s interval of the exercise. In comparison with the data obtained after the consumption of a mixed diet, after the consumption of a L-CHO diet resting plasma concentrations of β-HB [2.38 (0.18) vs 0.23 (0.01) mmol · l⁻¹, P < 0.001] and NA [4.81 (0.68) vs 2.2 (0.31) nmol · l⁻¹, P < 0.05] were higher, while glucose [4.6 (0.1) vs 5.7 (0.2) mmol · l⁻¹, P < 0.05] and insulin concentrations [11.9 (0.9) vs 21.8 (1.8) mU · l⁻¹] were lower. The 1-h post-exercise excess of V˙O₂ [9.1 (0.25) vs 10.6 (0.25) l, P < 0.05], and blood LA measured 3 min after the exercise [9.5 (0.4) vs 10.6 (0.5) mmol · l⁻¹, P < 0.05] were lower following the L-CHO treatment, whilst plasma NA and A concentrations reached higher values [2.24 (0.40) vs 1.21 (0.13) nmol · l⁻¹ and 14.30 (1.41) vs 8.20 (1.31) nmol · l⁻¹, P < 0.01, respectively]. In subjects on the L-CHO diet, the plasma β-HB concentration decreased quickly after exercise, attaining ≈30% of the pre-exercise value within 60 min, while insulin and glucose levels were elevated. The main conclusions of this study are: (1) a L-CHO diet is detrimental to anaerobic work capacity, possibly because of a reduced muscle glycogen store and decreased rate of glycolysis; (2) reduced carbohydrate intake for 3 days enhances activity of the sympathoadrenal system at rest and after exercise. Accepted: 31 January 1997     

The effect of a taurine-containing drink on performance in 10 endurance-athletes

Summary To determine the effect of a taurine-enriched drink Red Bull on performance, 10 endurance-athletes performed three trials. After 60 min. cycling at approximately 70% VO₂ max, the subjects pedalled to exhaustion on a cycle ergometer. During each exercise, the subjects received 500 ml of a test-drink after 30 min. submaximal cycling: Red Bull without taurine, without glucuronolacton (U1), Red Bull without taurine, without glucuronolacton, without caffeine (U2) and Red Bull original drink containing taurine, glucuronolacton and caffeine (U3).The heart rate level was significantly lower in U3 (p = 0,0031) 15 min. after application. The plasma catecholamines increased slightly from begin of exercise to 15 min. after application of the drinks in all trials but remained on a significantly lower level in U3 (epinephrine (p = 0,0011) and norepinephrine (p = 0,0003). Endurance time was significantly longer with Red Bull original in U3 (p = 0,015). The results of this study show a positive effect of a taurine-containing drink on hormonal responses which leads to a higher performance.     

The effect of alkanes on the physiology and metabolism of the entomopathogenic fungus,Isaria fumosorosea

The influence of different alkanes on spore morphology, glyoxlate pathway enzyme activities, total lipid contents and fatty acid composition of Isaria fumosorosea were investigated under laboratory conditions. Fungal spores grown on different alkanes showed higher germination and mycelial growth when compared to control. A strong induction of glyoxlate cycle enzymes in cell-free extracts was observed for cells grown on different alkanes when compared to glucose and control. Higher activities of glyoxlate cycle enzymes were observed for cells grown on alkanes when compared to other treatments. Even numbered fatty acids accounted for the majority of fatty acid production with a significant increase in relative amounts of linoleic acid and palmatic acid observed for conidia grown on alkanes. These results indicate that addition of alkanes to culture media can be a tool to pre-induce metabolic adaptations that can facilitate successful infection of insect host by entomopathogenic fungi.     

Changes in various plasma lipid components, glucose, and insulin in Spermophilus lateralis during hibernation

This study evaluated fat mobilization as related to gluconeogenesis in two age groups of hibernating golden-mantled ground squirrels (Spermophilus lateralis). Our experimental group consisted of a total of 16 male and 15 female squirrels. Plasma samples were collected from selected animals being killed weekly from January to March, and the concentration of triglycerides, glycerol (GY), free fatty acids (FFA), total cholesterol, lipase activity, glucose, and insulin, were determined by biochemical assays and radioimmunoassay. Our results showed a mean FFA/GY ratio of five, which was higher than the predicted value of three, suggesting a significant depletion of GY and an enhanced rate of gluconeogenesis via GY to maintain glucose homeostasis in the hibernating animals. The factor of age did not significantly affect plasma lipid components. However, in the male group, plasma glucose levels were significantly higher for adults than for juveniles. Overall, females had significantly higher plasma glucose levels than males (150 ± 11 vs. 110 ± 8 mg%, P < 0.05). In the adult group, a gender influence was also seen on plasma insulin levels, with females' being higher than males' (66 ± 13 vs. 25 ± 3 μIU/ml, P < 0.01). We suggest that during hibernation, female squirrels may have a higher rate of lipolysis and gluconeogenesis along with a lower glucose utilization than their male counterparts. Additionally, adult females may exhibit a higher peripheral insulin resistance during hibernation than adult males, a possibility which merits further study.     

Fructose-induced hepatic gluconeogenesis: effect of L-carnitine

High fructose feeding (60 g/100 g diet) in rodents induces alterations in both glucose and lipid metabolism. The present study was aimed to evaluate whether intraperitoneal carnitine (CA), a transporter of fatty acyl-CoA into the mitochondria, could attenuate derangements in carbohydrate metabolizing enzymes and glucose overproduction in high fructose-diet fed rats. Male Wistar rats of body weight 150-160 g were divided into 4 groups of 6 rats each. Groups 1 and 4 animals received control diet while the groups 2 and 3 rats received high fructose-diet. Groups 3 and 4 animals were treated with CA (300 mg/Kg body weight/day, i.p.) for 30 days. At the end of the experimental period, levels of carnitine, glucose, insulin, lactate, pyruvate, glycerol, triglycerides and free fatty acids in plasma were determined. The activities of carbohydrate metabolizing enzymes and glycogen content in liver and muscle were assayed. Hepatocytes isolated from liver were studied for the gluconeogenic activity in the presence of substrates such as pyruvate, lactate, glycerol, fructose and alanine. Fructose-diet fed animals showed alterations in glucose metabolizing enzymes, increased circulating levels of gluconeogenic substrates and depletion of glycogen in liver and muscle. There was increased glucose output from hepatocytes of animals fed fructose-diet alone with all the gluconeogenic substrates. The abnormalities associated with fructose feeding such as increased gluconeogenesis, reduced glycogen content and other parameters were brought back to near normal levels by CA. Hepatocytes from these animals showed significant inhibition of glucose production from pyruvate (74.3%), lactate (65.4%), glycerol (69.6%), fructose (56.2%) and alanine (63.6%) as compared to CA untreated fructose-fed animals. The benefits observed could be attributed to the effect of CA on fatty acyl-CoA transport.     

The effect of acid-base balance on fatigue of skeletal muscle

H+ ions are generated rapidly when muscles are maximally activated. This results in an intracellular proton load. Typical proton loads in active muscles reach a level of 20-25 mumol X g-1, resulting in a fall in intracellular pH of 0.3-0.5 units in mammalian muscle and 0.6-0.8 units in frog muscle. In isolated frog muscles stimulated to fatigue a proton load of this magnitude is developed, and at the same time maximum isometric force is suppressed by 70-80%. Proton loss is slowed when external pH is kept low. This is paralleled by a slow recovery of contractile tension and seems to support the idea that suppression results from intracellular acidosis. Nonfatigued muscles subjected to similar intracellular proton loads by high CO2 levels show a suppression of maximal tension by only about 30%. This indicates that only a part of the suppression during fatigue is normally due to the direct effect of intracellular acidosis. Further evidence for a component of fatigue that is not due to intracellular acidosis is provided by the fact that some muscle preparations (rat diaphragm) can be fatigued with very little lactate accumulation and very low proton loads. Even under these conditions, a low external pH (6.2) can slow recovery of tension development 10-fold compared with normal pH (7.4). We must conclude that there are at least two components to fatigue. One, due to a direct effect of intracellular acidosis, acting directly on the myofibrils, accounts for a part of the suppression of contractile force. A second, which in many cases may be the major component, is not dependent on intracellular acidosis. This component seems to be due to a change of state in one or more of the steps of the excitation-contraction coupling process. Reversal of this state is sensitive to external pH which suggests that this component is accessible from the outside of the cell.     

Effect of prolonged exercise on the level of triglycerides in the rat liver

This study examined the effect of prolonged exercise on the level of triglycerides (TG) in rat liver. The rats were divided into groups: 1-control, 2-treated with nicotinic acid, 3-fed with glucose during exercise, 4-fasted, 5-adrenalectomized, 6-adrenalectomized and fed with oil. In the control group, there was gradual accumulation of TG in the liver and their level was doubled at exhaustion as compared to the resting value. Nicotinic acid lowered the resting level of TG and prevented their accumulation during exercise. Administration of glucose during exercise partially prevented the increase in TG level in the liver. In rats fasted for 24 h before exercise, the net increase in liver TG level during exercise was similar to that in the controls. Adrenalectomy, like nicotinic acid, lowered TG level at rest and prevented its increase during exercise. Feeding the adrenalectomized rats with oil elevated the plasma free fatty acid level but did not result in accumulation of TG in the liver, either at rest or during exercise. It is concluded that prolonged exercise results in accumulation of TG in the liver and that the process depends on the supply of free fatty acids and glucose and requires the presence of glucocorticoids.     

The effect of hypoxia on performance during 30 s or 45 s of supramaximal exercise

The purpose of this study was to evaluate the effect of hypoxia (10.8 +/- 0.6% oxygen) on performance of 30 s and 45 s of supramaximal dynamic exercise. Twelve males were randomly allocated to perform either a 30 s or 45 s Wingate test (WT) on two occasions (hypoxia and room air) with a minimum of 1 week between tests. After a 5-min warm-up at 120 W subjects breathed the appropriate gas mixture from a wet spirometer during a 5-min rest period. Resting blood oxygen saturation was monitored with an ear oximeter and averaged 97.8 +/- 1.5% and 83.2 +/- 1.9% for the air (normoxic) and hypoxic conditions, respectively, immediately prior to the WT. Following all WT trials, subjects breathed room air for a 10-min passive recovery period. Muscle biopsies from the vastus lateralis were taken prior to and immediately following WT. Arterialized blood samples, for lactate and blood gases, were taken before and after both the warm-up and the performance of WT, and throughout the recovery period. Open-circuit spirometry was used to calculate the total oxygen consumption (VO2), carbon dioxide production and expired ventilation during WT. Hypoxia did not impair the performance of the 30-s or 45-s WT. VO2 was reduced during the 45-s hypoxic WT (1.71 +/- 0.21 l) compared with the normoxic trial (2.16 +/- 0.26 l), but there was no change during the 30-s test (1.22 +/- 0.11 vs 1.04 +/- 0.17 l for the normoxic and hypoxic conditions, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)     

The effect of exercise and restraint on pectoral muscle metabolism in pigeons

The effect of various activity regimes on metabolism of pigeon pectoralis was examined by measurement of blood lactate following exercise, total lactate dehydrogenase activity of pectoral muscle, and proportions of specific isoenzymes of pectoral muscle lactate dehydrogenase. Sprint-trained birds had the highest pectoral muscle lactate dehydrogenase activity (1409 IU · g⁻¹ wet tissue), while endurance-trained birds had the highest peak lactate levels (287 mg · dl⁻¹, extrapolated from decay curves) and fastest half-time of the lactate response (4.8 min) following exercise, but the lowest lactate dehydrogenase activity (115 IU · g⁻¹ wet tissue). Immobilization of one wing for 3 weeks following endurance training produced a marked increase in lactate dehydrogenase activity of the immobilized muscle, compared to that in the contralateral pectoralis and endurance-trained muscle. Aerobic forms of the lactate dehydrogenase enzyme (that favor conversion of lactate to pyruvate) predominated in pectoral muscle of endurance-trained birds, while cage-confined birds exhibited primarily the anaerobic isoenzymes. These results demonstrate that conversion of pectoral muscle lactate dehydrogenase isoenzymes, total lactate dehydrogenase activity, and half-time of lactate response after exercise is dependent on activity regime in pigeons. In this respect, pigeon pectoral muscle responds to training and disuse in a manner similar to that of mammalian skeletal muscle. Accepted: 10 September 1996     

Leptin、TNF-alpha、FFA 在肥胖症患者血清中的表达及临床意义

目的：研究瘦素（Leptin）、肿瘤坏死因子alpha（TNF-alpha）和游离脂肪酸（FFA）在肥胖患者血清中的表达以及其临床意义。方法：选 取2013 年5 月到2014 年5 月我院体检的肥胖症患者30 例（研究组）,另选取非肥胖症者30 例（对照组）,测量两组空腹血糖 （FPG）、空腹胰岛素（FINS）、血脂和Leptin、TNF- alpha、FFA 等指标,并比较两组之间的差异,观察Leptin、TNF- alpha、FFA 和肥胖相关指 标的相关关系。结果：研究组甘油三脂（TG）、极低密度脂蛋白- 胆固醇（VLDL-C）、Leptin、FINS 、FPG、TNF- alpha、FFA 以及HOMA 模型胰岛素抵抗指数（HOMA-IR）分别为（1.98± 0.31）mmol/L、（0.76± 0.02）mmol/L、（15.14± 0.04）ug/L、（20.56± 0.04）mmol/L、 （5.93± 0.04）mmol/L、（43.98± 0.14）ng/L、（0.17± 0.01）mmol/L 和（5.37± 0.25）均显著高于对照组,两组比较差异具有统计学意 义（t=9.423,8.979,9.074,10.082,9.089,9.562,9.065,10.083,均P＜0.05）;研究组胰岛素敏感指数（ISI）为（0.011± 0.002）显著低于 对照组（0.021± 0.001）,两组比较差异具有统计学意义（t=11.428,P=0.012）;FFA 与TG、HOMA-IR、FINS 呈正相关关系（r=0. 842,0.796,0.879,P=0.017.0.019,0.023）,与ISI 呈负相关关系（r=-0.958,P=0.021）;Leptin 与BMI、HOMA-IR、FINS 呈正相关关系 （r=0.793,0.869,0.837,P=0.018,0.022,0.017）,与ISI 呈负相关关系（r=-0.905,P=0.011）;TNF-alpha与ISI 呈负相关关系（r=-0.807, P=0.013）。结论：肥胖者血清中Leptin、TNF- alpha、FFA 显著高于正常者,且和肥胖等项指标具有相关关系。     

Alterations in lipid and calcium metabolism associated with seizure activity in the postischemic brain

Transient ischemia is known to lead to a long-lasting depression of cerebral metabolic rate and blood flow and to an attenuated metabolic and circulatory response to physiological stimuli. However, the corresponding responses to induced seizures are retained, demonstrating preserved metabolic and circulatory capacity. The objective of the present study was to explore how a preceding period of ischemia (15 min) alters the release of free fatty acids (FFAs) and diacylglycerides (DAGs), the formation of cyclic nucleotides, and the influx/efflux of Ca(2+), following intense neuronal stimulation. For that purpose, seizure activity was induced with bicuculline for 30 s or 5 min at 6 h after the ischemia. Extracellular Ca(2+) concentration (Ca(2+)(e)) was recorded, and the tissue was frozen in situ for measurements of levels of FFAs, DAGs, and cyclic nucleotides. Six hours after ischemia, the FFA concentrations were normalized, but there was a lowering of the content of 20:4 in the DAG fraction. Cyclic AMP levels returned to normal values, but cyclic GMP content was reduced. Seizures induced in postischemic animals showed similar changes in Ca(2+)(e), as well as in levels of FFAs, DAGs, and cyclic nucleotides, as did seizures induced in nonischemic control animals, with the exception of an attenuated rise in 20:4 content in the DAG fraction. We conclude that, at least in the neocortex, seizure-induced phospholipid hydrolysis and cyclic cAMP/cyclic GMP formation are not altered by a preceding period of ischemia, nor is there a change in the influx/efflux of Ca(2+) during seizure discharge or in associated spreading depression.     

Chronobiological effects on exercise performance and selected physiological responses

Previous studies investigating the impact of circadian rhythms on physiological variables during exercise have yielded conflicting results. The purpose of the present investigation was to examine maximal aerobic exercise performance, as well as the physiological and psychophysiological responses to exercise, at four different intervals (0800 hours, 1200 hours, 1600 hours, and 2000 hours) within the segment of the 24-h day in which strenuous physical activity is typically performed. Ten physically fit, but untrained, male university students served as subjects. The results revealed that exercise performance was unaffected by chronobiological effects. Similarly, oxygen uptake, minute ventilation and heart rate showed no time of day influences under pre-, submaximal, and maximal exercise conditions. Ratings of perceived exertion were unaffected by time of day effects during submaximal and maximal exercise. In contrast, rectal temperature exhibited a significant chronobiological rhythm under all three conditions. Under pre- and submaximal exercise conditions, significant time of day effects were noted for respiratory exchange ratio, while a significant rhythmicity of blood pressure was evident during maximal exercise. However, none of these physiological variables exhibited significant differential responses (percent change from pre-exercise values) to the exercise stimulus at any of the four time points selected for study. Conversely, resting plasma lactate levels and lactate responses to maximal exercise were found to be significantly sensitive to chronobiological influences. Absolute post-exercise plasma norepinephrine values, and norepinephrine responses to exercise (percent change from pre-exercise values), also fluctuated significantly among the time points studied. In summary, these data suggest that aerobic exercise performance does not vary during the time frame within which exercise is normally conducted, despite the fact that some important physiological responses to exercise do fluctuate within that time period. Accepted: 18 August 1997     

Effects of soybean oil supplementation on performance,digestion and metabolism of early lactation dairy cows fed sugarcane-based diets

Sugarcane is an important forage source for dairy cows in tropical countries. However, it provides limited digestible fiber and energy intake, and fat supplementation can be a way to increase energy density and decrease dietary, non-fiber carbohydrates concentrations. We aimed to evaluate the performance, digestion and metabolism of dairy cows in early lactation fed different concentrations of soybean oil (SBO) in sugarcane-based diets. Fourteen primiparous (545±17.2 kg of BW) and eight multiparous (629±26.7 kg BW) Holstein dairy cows were used according to a randomized block design. After calving, diets were randomly assigned to cows within the two parity groups. Diets were formulated with increasing concentrations of SBO (g/kg dry matter (DM)): control (0), low (LSBO; 15.7), medium (MSBO; 44.3) and high (HSBO; 73.4). The study was performed from calving until 84 days in milk, divided into three periods of 28 days each. Dry matter intake (DMI) was affected quadratically in response to SBO addition with the greatest and lowest values of 19.0 and 16.0 kg/day for LSBO and HSBO diets, respectively. The digestibility of potentially digestible NDF was quadratically affected by SBO with the greatest value of 623 g/kg for LSBO diet. Both milk and energy-corrected milk (ECM) production were quadratically affected by SBO inclusion, with greatest ECM values of 27.9 and 27.3 for LSBO and MSBO, respectively. Soybean oil inclusion linearly decreased milk fat concentration by 13.2% from control to HSBO. The CLA t10,c12-18:2 was observed in milk fat only for MSBO and HSBO diets. Soybean oil inclusion did not affect plasma glucose or serum concentrations of total proteins, globulins, albumin, urea nitrogen, beta-hydroxybutyrate, non-esterified fatty acids or insulin. Serum concentrations of total cholesterol, triglycerides and low-density lipoprotein increased with SBO supplementation. Soybean oil inclusion in sugarcane-based diets for early lactation dairy cows from 15.7 to 44.3 g/kg DM can improve energy intake and performance; however, at 44.3 g/kg DM milk fat concentration and ECM decreased. Soybean oil inclusion at 73.4 g/kg DM adversely affected energy intake, fiber digestion and performance of early lactation dairy cows and is not recommended.     

Effects of feeding on metabolism, gas transport, and acid-base balance in the bullfrog Rana catesbeiana

Massive feeding in ectothermic vertebrates causes changes in metabolism and acid-base and respiratory parameters. Most investigations have focused on only one aspect of these complex changes, and different species have been used, making comparison among studies difficult. The purpose of the present study was, therefore, to provide an integrative study of the multiple physiological changes taking place after feeding. Bullfrogs (Rana catesbeiana) partly submerged in water were fed meals (mice or rats) amounting to approximately (1)/(10) of their body weight. Oxygen consumption increased and peaked at a value three times the predigestive level 72-96 h after feeding. Arterial PO(2) decreased slightly during digestion, whereas hemoglobin-bound oxygen saturation was unaffected. Yet, arterial blood oxygen content was pronouncedly elevated because of a 60% increase in hematocrit, which appeared mediated via release of red blood cells from the spleen. Gastric acid secretion was associated with a 60% increase in plasma HCO3(-) concentration ([HCO3(-)]) 48 h after feeding. Arterial pH only increased from 7.86 to 7.94, because the metabolic alkalosis was countered by an increase in PCO(2) from 10.8 to 13.7 mm Hg. Feeding also induced a small intracellular alkalosis in the sartorius muscle. Arterial pH and HCO3(-) returned to control values 96-120 h after feeding. There was no sign of anaerobic energy production during digestion as plasma and tissue lactate levels remained low and intracellular ATP concentration stayed high. However, phosphocreatine was reduced in the sartorius muscle and ventricle 48 h after feeding.     

Eicosapentaenoic acid and docosahexaenoic acid effects on tumour mitochondrial metabolism, acyl CoA metabolism and cell proliferation

In order to investigate the effects of high-fat diets rich in eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), Wistar rats bearing subcutaneous implants of the Walker 256 tumour were fed pelleted chow containing low DHA/EPA or high DHA/EPA. The presence of n-3 polyunsaturated fatty acids (PUFAs) led to a marked suppression (35-46%) of tumour growth over a 12 day period. Both the whole tumour homogenate and the Percoll-purified mitochondrial fraction presented significant changes in fatty acid composition. The levels of EPA increased in both n-3 dietary groups while the levels of DHA increased only in the high DHA/EPA group, in comparison with the control chow-fed group. The presence of n-3 PUFAs led to an increase in mitochondrial acyl CoA synthetase activity, but neither the cytoplasmic acyl CoA content nor the n-3 fatty acid composition of the cytoplasmic acyl CoAs was altered by the diet. The content of thiobarbituric acid-reactive substances (TBARS) was increased in the low DHA/EPA group but was unchanged in the high DHA/EPA group. In vitro studies with the Walker 256 cell line showed a 46% decrease in cell growth in the presence of either EPA or DHA which was accompanied by a large decrease in the measured mitochondrial membrane potential. The TBARS content was increased only in the EPA-exposed cells. Cell cycle analysis identified a decrease in G0-G1 phase cells and an increase in G2-M phase cells and apoptotic cells, for both EPA and DHA-exposed cells. The data show that the presence of n-3 PUFAs in the diet is able to significantly after the growth rate of the Walker 256 tumour. The involvement of changes in mitochondrial membrane composition and membrane potential have been indicated for both EPA and DHA, while changes in lipid peroxidation have been identified in the presence of EPA but not of DHA.