U-14C]glucose, -alanine, and -leucine oxidation in rats at rest and two intensities of running

The oxidations of injected [U-14C]glucose, [U-14C]alanine, and [U-14C]leucine were investigated in laboratory rats during rest or 2 h of easy and hard treadmill running. After [U-14C]glucose injection, the rate and magnitude of 14CO2 evolution were relatively low at rest and increased as a linear function of metabolic rate (VO2). Evolution of 14CO2 after [U-14C]alanine injection was faster and larger during exercise than rest. The peak of alanine decarboxylation occurred before glucose and, therefore, did not reflect conversion of alanine to glucose prior to decarboxylation. The rate and magnitude of 14CO2 evolution after [U-14C]leucine injection were proportional to metabolic rate, but less than after glucose or alanine injection. During exercise, levels of alanine and leucine in muscle and blood were unchanged or elevated compared to rest. During exercise, alanine levels were unchanged or increased in liver. Liver leucine levels were depressed when exercise began, but increased toward control values during exercise. The metabolism of selected amino acids is joined to carbon flow sustaining exercise.     

The effects of performing isometric training at two exercise intensities in healthy young males

No previous studies have examined the effects of isometric training intensity upon resting blood pressure (BP). The aims of this study were (a) to compare the effects of leg isometric training, performed at two intensities, upon resting systolic-SBP, diastolic-DBP and mean arterial-MAP BP; and (b) to examine selected cardiovascular variables, in an attempt to explain any changes in resting BP following training. Thirty-three participants were randomly allocated to either control, high- (HI) or low-intensity (LI) training for 8 weeks. Participants performed 4 × 2 min exercise bouts 3× weekly. Resting BP was measured at baseline, 4-weeks and post-training. SBP, DBP and MAP fell significantly in both groups after training. Changes were –5.2 ± 4.0, –2.6 ± 2.9 and –2.5 ± 2.2 mmHg [HI]; –3.7 ± 3.7, –2.5 ± 4.8 and –2.6 ± 2.5 mmHg [LI] for SBP, DBP and MAP, respectively. There were no significant changes in BP at 4 weeks. No significant changes were observed in any of the other cardiovascular variables examined. These findings suggest that isometric training causes reductions in SBP, DBP and MAP at a range of exercise intensities, when it is performed over 8 weeks. Furthermore, it is possible to reduce resting BP using a much lower isometric exercise intensity than has previously been shown.     

Effects of physical training on cardiac myosin ATPase activity.

Cardiac myosin from rats exercised 90 or 150 min daily for 8 wk was compared with the myosin from the hearts of matched sedentary controls. The Ca++-ATPase activity was increased 17 percent in rats exercised 90 min and 30 percent in rats exercised 150 min daily. In the exercised group 0.18 M KCl increased the myosin ATPase activity by 50 percent but had no effect in the control group. Ethylene glycol activated the Ca++-ATPase in control myosin preparations, but had no significant effect on myosin from conditioned hearts. Heavy meromyosin (HMM) from conditioned hearts had a higher Ca++-ATPase activity than from controls. Fluorescence with 8-anilinonaphthalene sulfonate (ANS) was increased 30 percent in HMM from conditioned hearts. The results suggest that the increased myosin ATPase activity in the hearts of exercised animals may be due to a local conformational change at or near the active site.     

The effect of running training on exercise-induced asthma

A running training program had no effect upon the severity of exercise-induced asthma, however, it appeared as if the children benefitted not only from a decrease in the frequency and duration of asthma in daily life, but also by improvement in self-confidence and ability to participate in group activities.     

The effect of plyometric training on distance running performance

Previous research has reported that plyometric training improves running economy (RE) and ultimately distance-running performance, although the exact mechanism by which this occurs remains unclear. This study examined whether changes in running performance resulting from plyometric training were related to alterations in lower leg musculotendinous stiffness (MTS). Seventeen male runners were pre- and post-tested for lower leg MTS, maximum isometric force, rate of force development, 5-bound distance test (5BT), counter movement jump (CMJ) height , RE, V˙O_2max, lactate threshold (Th_la), and 3-km time. Subjects were randomly split into an experimental (E) group which completed 6 weeks of plyometric training in conjunction with their normal running training, and a control (C) group which trained as normal. Following the training period, the E group significantly improved 3-km performance (2.7%) and RE at each of the tested velocities, while no changes in V˙O_2max or Th_la were recorded. CMJ height, 5BT, and MTS also increased significantly. No significant changes were observed in any measures for the C group. The results clearly demonstrated that a 6-week plyometric programme led to improvements in 3-km running performance. It is postulated that the increase in MTS resulted in improved RE. We speculate that the improved RE led to changes in 3-km running performance, as there were no corresponding alterations in V˙O_2max or Th_la. Electronic Publication     

Physiological and muscle enzyme adaptations to two different intensities of swim training

Summary To test the hypothesis that a smaller quantity of high intensity (HI) as opposed to a larger quantity of moderate intensity (MI) swim training would result in adaptations more specific to the short performance times of swimming competitions, two groups of elite university swimmers were tested before and after 6.5 weeks of specific HI or MI intermittent swim training. In training, swimming times were faster and blood lactate concentrations were higher (10.2 vs. 7.5 mM) during HI compared to MI training. No significant differences were observed between the two groups for any of the variables measured, before or after training. However, significant increases with training were observed for the activities of hexokinase, phosphorylase, phosphofructokinase, succinate dehydrogenase, and 3-hydroxyacyl CoA dehydrogenase in the deltoid, but not the gastrocnemius muscles. Training resulted in significant increases in O₂ max during treatmill running, but not during tethered swimming. It is concluded that a larger quantity of MI swim training results in physiological adaptations that are similar to those obtained with a smaller quantity of HI training, at least over a relatively short training period.This study was supported by a grant from the Natural Sciences and Engineering Research Council of Canada     

Lack of effect of habenula lesion on heroin self-administration in rats

We examined the effects of bilateral electric lesion of the habenula (Hb) on the acquisition and maintenance of heroin self-administration. The rats were trained to self-administer heroin (0.05 mg/kg/infusion) under FR1 schedule in daily 4 h sessions. A progressive ratio schedule (PR3-4) was used to evaluate the relative motivational value of heroin reinforcement. Compared with the controls, neither pre-training nor post-training of Hb lesions had any effects on the total amount of infusions and motivational value of heroin reward. However, pre-training Hb lesion caused transient active and inactive nose-poke responding in the early phase of training, suggesting increased locomotor exploration. The results suggest that Hb might not play an important role in mediating the acute reinforcing effect of heroin.     

Body composition, resting and running metabolic rates, and net cost of running in rats during starvation

Resting metabolic rate decreases during starvation. However, effects of starvation on the cost of running are not clear. The aim of this study was to examine the effects of 5 days starvation on body composition, resting metabolic rates, running metabolic rates, and net cost of running in male rats. Five days starvation resulted in reductions of 70% fat, 8% protein and 12% carbohydrates. Mass(-0.75) specific resting metabolic rate was significantly reduced from 3.69 +/- 0.27 to 2.73 +/- 0.17 W kg(-0.75) after 5 days starvation. The reduction in metabolic rate after 5 days starvation was maintained during running, in that running metabolic rate was reduced from 10.65 +/- 0.41 to 8.97 +/- 0.47 W kg(-0.75). The net costs of running were calculated and expressed as the costs of moving 1 kg a distance of 1 m. After 5 days of starvation it was reduced from 31.16 +/- 2.03-29.79 +/- 1.69 J m(-1) kg(-1). The reduction however was not significant. The present results therefore suggest that 5 days starvation resulted in a metabolic depression of the resting metabolic rate that was maintained during running. However, the net cost of running remained unchanged, suggesting that the muscle tissues are not significantly involved in the metabolic changes during starvation.     

The effect of recreational soccer training and running on postural balance in untrained men

The aim of this study was to examine the effect of intense intermittent exercise performed as soccer training or interval running in comparison with continuous endurance running exercise on postural balance in young healthy untrained males. Young sedentary men were randomized to soccer training (SOC, n = 10), continuous running (RUN; n = 9), high-intensity interval running (INT; n = 7) or no training (CON; n = 9). Postural balance was evaluated pre and post 12 weeks of training using a 30-s single-leg stance test on a force plate (AMTI) to yield center of pressure (CoP) sway path and 1-min beam standing (Flamingo test). CoP sway length decreased by 18.2% (p < 0.01), 14.6% (p < 0.05) and 12.8% (p < 0.05) in SOC, INT and RUN, respectively. CoP sway area decreased in SOC (−30.2%; p < 0.01) and INT (−23.4%; p < 0.01) but remained unaffected in RUN. Acceleration parameters (Mean CoP acc, SD accX, SD accY) decreased in SOC only (17–19%, p < 0.05). All training groups demonstrated fewer falls (37–41%, p < 0.01) in the Flamingo test. No changes were observed in CON. Relationships (r > 0.40) were observed between pre-training values in CoP sway area versus muscle fiber area, explosive muscle strength and countermovement jump velocity. Postural control was improved in response to 12 weeks of soccer training and high-intensity interval running, respectively, while less-marked changes were observed following continuous running. Notably, the reduced variability in CoP acceleration after soccer training indicates that this training regimen may produce superior improvements in postural sensory-motor function.     

Lack of cardiotoxic effect of isoproterenol in streptozotocin diabetic rats

Summary The well known cardiotoxic effect of isoproterenol (ISO) was investigated in normal and streptozotocin diabetic rats. Seven days after the subcutaneous injection of ISO (15 mg/kg) the hearts were perfusion fixed and 12 sections from each heart were stained (Masson's trichrome). ISO induced myocardial fibrosis was quantified at the light microscopic level according to established morphometric principles. Pulse rate and ST elevation were recorded by EEC (3 standard leads) before and after the ISO injection. Non-diabetic control animals showed marked fibrosis after ISO, but surprisingly the diabetic animals showed no fibrosis after ISO treatment. These findings were in accordance with an ISO induced ST elevation seen only among control animals although both groups showed the same degree of tachycardia. Insulin treatment prevented the protection against ISO and when streptozotocin was injected 24 h after the ISO a normal quantitative and qualitative appearance of the scar tissue was seen. It thus seems that streptozotocin diabetic rats are protected against the toxic effect of ISO, leaving the haemodynamic response unaffected. Which factor in the diabetic metabolism is reponsible for the present phenomenon is not known, but a defect in the signal transmission from the -receptor to the adenylcyclase is suggested as a possible explanation.     

Unusual fast myosin isozyme pattern in the lateral gastrocnemius of the chicken

Summary The myosin isozyme composition of the lateral gastrocnemius muscle of the chicken leg was investigated during various stages of development utilizing non-denaturing pyrophosphate gel electrophoresis, two-dimensional gel electrophoresis and peptide mapping techniques. An unusual isoform pattern for fast myosin in the lateral gastrocnemius muscle of the adult chicken leg was demonstrated which consisted of a predominance of myosin homodimers and lesser amounts of myosin heterodimer. In addition, a different myosin heavy chain isoform was present in the adult chicken lateral gastrocnemius muscle when compared to other adult fast-twitch muscles. While the adult lateral gastrocnemius muscle contained a different myosin heavy chain isoform from other adult fast-twitch muscles, the embryonic lateral gastrocnemius muscle contained a myosin heavy chain identical to that of the embryonic pectoralis major.     

The effect of exercise training on restraint ulcers in rats

The effect of chronic treadmill running on susceptibility to restraint-cold-induced ulcers was studied in two strains of rats: Long-Evans and Sprague-Dawley. Runners were progressively trained for 8 weeks, reaching a rate of 1 mph for 1 hr daily, 5 days per week after the 4th week. Walkers were exposed to the treadmill environment 3 days per week (0.2 mph for 10 min). Sedentary groups remained in their home cages. After 8 weeks the rats were starved for 24 hrs, immobilized in restraint cages and placed in the refrigerator (5° C) for 4 hrs. Animals were then sacrificed and their stomachs examined for ulcerative lesions. No significant differences in number of ulcers or ulcer indexes per stomach were found between groups within each rat strain or between strains. These results suggest that treadmill running provides no protection against gastric ulceration induced by restraint-cold stress. The complex variables involved in ulcer research are discussed and suggestions presented for future work on the anti-ulcer effect of exercise.Supported in part by the University of Nebraska Research Council Summer Fellowship.     

The effect of forced running on heat production in brown adipose tissue in rats

The effect of running on heat production in brown adipose tissue (BAT) was compared between trained and untrained rats. Rats were forced to run a treadmill while temperatures of colon (T col) and interscapular BAT (T bat) were measured. The daily running for 5 weeks neither changed the size of interscapular BAT nor the norepinephrine-induced thermogenesis (8 micrograms/kg X min). During running, both T bat and T col increased. In rats trained for 2 weeks, the increases in T bat were similar to those in T col. In untrained rats, however, the increases in T bat were larger than those in T col. It is suggested that exercise increases heat production in BAT in untrained rats, but such heat production in BAT is abolished by daily exercise. Exercise suppresses cold-induced heat production in BAT of trained rats.     

Lack of coordinated changes in metabolic enzymes and myosin heavy chain isoforms in regenerated muscles of trained rats

We investigated training-induced changes in biochemical properties and myosin heavy chain (MHC) composition of regenerated (cardiotoxin-injected) plantaris muscles (PLA) in rats either maintained sedentary (S, n = 9) or endurance trained on a treadmill over a 8-week period (T, n = 7). Both endurance training and regeneration altered the pattern of fast MHC expression. An analysis of the two-way interaction between training and regeneration showed that the relative content of type IIa MHC was affected (P < 0.05). The 140% increase in type IIa MHC observed in regenerated PLA from T rats compared with nontreated muscle of S rats, exceeded the 102% increase resulting from the combination of regeneration alone (26%) and training alone (61%). A similar interaction between training and regeneration was shown for the percentage of fibres expressing either type IIa or type IIb MHC (P < 0.05). In contrast, a significant increase in the citrate synthase (CS) activity was shown in PLA as a result of endurance training, without specific effect of regeneration. Furthermore, training-induced changes in CK and LDH isoenzyme distribution occurred to a similar extent in regenerated and non-treated PLA muscles, and thus did not follow the changes in MHC isoforms. An increase in the mitochondrial CK isozyme activity (mi-CK) was shown in both non-treated and previously degenerated PLA muscles (123 and 117%, P < 0.01, respectively), without specific effect of regeneration. The ratio of mi-CK to CS activity, an estimate of the mitochondrial specific activity of mi-CK was significantly increased by training (P < 0.02) and decreased by regeneration (P < 0.05). Taken together, these data suggest that while training and regeneration have cumulative effects on the pattern of fast MHC expression, the training-induced changes in the energy metabolism shown in mature non-treated myofibres are similar to those observed in regenerated fibres.     

Paradoxical enhancement of long-term potentiation in poor-learning rats at low test stimulus intensities

Much empirical evidence and numerous theoretical models point to modification of synaptic efficacy as a mechanism for memory formation. To evaluate theoretical models, it is necessary to obtain quantitative experimental data relating learning to experimentally induced synaptic efficacy changes (such as long-term potentiation, LTP). An important problem in this type of experiment is how to quantify the LTP induced by a given stimulation protocol. Of relevance is the informally well-known observation that LTP magnitude appears to vary as a function of the intensity of the stimulus used to evoke baseline responses. The present study found that using a measure of LTP that circumvents this variation, a strong negative correlation of learning with potentiation emerges. Spatial learning ability was compared with the magnitude of subsequent LTP induction as follows: rats underwent a day of spatial training in a watermaze followed by 5 days of bilateral perforant path tetanisation. Baseline electrophysiological responses were evoked over a range of stimulus intensities (input/output [IO] curves) before and after tetanisation. Although LTP was observed across the whole of the IO curve, it showed a smooth decline with increasing current. The animals were then grouped according to their watermaze performance and IO curves compared between good and poor learners. After tetanisation, there was a negative withinanimal correlation between learning and evoked potential size with weak test stimuli and a positive correlation with strong stimuli. The decline of LTP across the IO curve differed between good and poor spatial learners; the poor learners showed higher percentage potentiation with test stimuli close to zero intensity, but a faster decrease in LTP across the curves. The findings are therefore: (1) the measured amount of LTP declined systematically with increasing stimulus strength, and (2) the parameters of the decline correlated with spatial learning ability. These results raise two important issues. First, because measured LTP varied systematically across the IO curve, it appears that for quantitative analyses the widely used method of LTP measurement using a single test stimulus intensity risks missing significant features of the data. It is suggested that a measure be used that incorporates data from a range of stimulus intensities. Second, when such a measure is used there is a striking negative correlation of spatial learning ability with LTP. These apparently paradoxical results are discussed.     

Effects of running training on the blood glucose and lactate in rats during rest and swimming.

The purpose of this study was to examine the effect of physical training on the concentrations of glucose and lactate in the blood of rats during rest and after an acute bout of exercise. We used the following types and periods of training; (i) swimming for 4 weeks, (ii) running for 4 weeks, and (iii) running for 10 weeks. The results clearly show that the resting levels of blood glucose was significantly lower in groups trained by either swimming or running than untrained groups. In addition, after the acute exercise of swimming, animals trained by either running or swimming showed a lower increase in the blood lactate than untrained animals. Furthermore, the increases in the blood glucose after swimming were significantly lower in the group trained by swimming for 4 weeks and by running for 10 weeks than in untrained groups. These results suggest that after physical training by running, animals show an adaptation in the changes in the blood glucose and the blood lactate that are induced by a different type of physical stress, swimming.     

Reversible epigenetic modifications of the two cardiac myosin heavy chain genes during changes in expression

The two genes of the cardiac myosin heavy chain (MHC) locus-alpha-MHC (aMHC) and beta-MHC (bMHC)--are reciprocally regulated in the mouse ventricle during development and in adult conditions such as hypothyroidism and pathological cardiac hypertrophy. Their expressions are under the control of thyroid hormone T3 levels. To gain insights into the epigenetic mechanisms that underlie this inducible and reversible switching of the aMHC and bMHC isoforms, we have investigated the histone modification patterns that occur over the two cardiac MHC promoters during T3-mediated reversible switching of gene expression. Mice fed a diet of propylthiouracil (PTU, an inhibitor of T3 synthesis) for 2 weeks dramatically reduce aMHC mRNA expression and increase bMHC mRNA levels to high levels, while a subsequent withdrawal of PTU diet for 2 weeks completely reverses the T3-mediated changes in MHC expression. Using hearts from mice treated in this way, we carried out chromatin immunoprecipitation-qPCR assays with antibodies against acetylated histone H3 (H3ac) and trimethylated histone (H3K4me3)-two well-documented markers of activation. Our results show that the reexpression of bMHC is associated at the bMHC promoter with increased H3ac but not H3K4me3. In contrast, the silencing of aMHC is associated at its promoter with decreased H3K4me3, but not decreased H3ac. The epigenetic changes at the two MHC promoters are completely reversed when the gene expression returns to initial levels. These data indicate that during reciprocal and inducible gene expression H3ac parallels bMHC isoform expression while H3K4me3 parallels expression of the tightly linked aMHC isoform.