Central nitric oxide inhibition modifies metabolic adjustments induced by exercise in rats

Brain glucose metabolism: Role of nitric oxide

One possible reason for failure in achieving optimal glycemic control in patients with type 2 diabetes (T2D) is that less attention has been paid to the brain, a fundamental player in glucose homeostasis, that consumes about 25% of total glucose utilization. In addition, animal and human studies indicate that nitric oxide (NO) is a critical player in glucose metabolism. NO synthesis from L-arginine is lower in patients with T2D, and endothelial NO synthase (eNOS)-derived NO bioavailability is lower in T2D. NO in the nervous system plays a role in neurovascular coupling (NVC) and the hypothalamic control of glucose sensing and energy homeostasis, influencing glucose utilization. This review explores NO's role in the brain's glucose metabolism. Literature indicates that glucose metabolism is different between neurons and astrocytes. Unlike neurons, astrocytes have a higher rate of glycolysis and a greater ability for lactate production. Astrocytes produce a greater amount of NO than neurons. NO inhibits mitochondrial respiration in both neurons and astrocytes and decreases intracellular ATP. NO-induced inhibition of mitochondrial respiration in neurons is not accompanied by compensatory glycolysis because phosphofructokinase 2.3 (PFK2.3), the most potent activator of PFK1 and thus glycolysis, is subjected to ubiquitylation and proteasomal degradation by cadherin-1 (Cdh1)-activated anaphase-promoting complex/cyclosome (APC/C), which leads to a low glycolytic rate in neurons. In astrocytes, NO inhibits mitochondrial respiration, but astrocytes display compensatory glycolysis by activating the adenosine monophosphate (AMP)-activated protein kinase (AMPK) pathway.

Aerobic performance in rats subjected to incremental-speed running exercise: A multiple regression analysis study emphasizing thermoregulation-related variables

Single-variable analyses have limited ability to explain complex phenomena such as the regulation of prolonged physical (aerobic) performance. Our study aimed to identify predictors of performance in rats subjected to incremental-speed running exercise. Notably, most variables assessed were associated with rats' thermoregulation. We extracted data from 355 records obtained in 216 adult Wistar rats. Hierarchical multiple linear regression analyses were conducted to identify the predictive power of eight variables. The distance traveled, a performance index, was the dependent variable. The independent variables included body mass, biological sex, body core temperature (TCORE) measurement site, and the following thermoregulation-related variables: ambient temperature (TAMB), initial TCORE, exercise-induced change in TCORE (ΔTCORE), ΔTCORE from 0 to 10 min (ΔTCORE 0-10; when TCORE increase is fastest), and heat loss index (HLI). This analysis with eight variables revealed an adjusted R2 of 0.495; TAMB, ΔTCORE, body mass, and ΔTCORE 0-10 had the highest predictive powers (β values: -0.700, 0.463, -0.353, and -0.130, respectively). Additional analyses consisted of separate regressions for each TCORE index measured: abdominal (TABD), brain (TBRAIN), and colonic (TCOL) temperature. These analyses yielded adjusted R2 values of 0.608 (TABD), 0.550 (TBRAIN), and 0.437 (TCOL). Again, the distance traveled was primarily predicted by body mass and thermoregulation-related variables (TAMB, ΔTCORE, and ΔTCORE 0-10). Among these four variables, ΔTCORE was the only one with a positive β value (directly predicted performance), while the others had negative values. Collectively, these findings advance our understanding of performance regulation in rats, especially regarding the role of thermoregulation-related variables.

Effects of Tryptophan and Physical Exercise on the Modulation of Mechanical Hypersensitivity in a Fibromyalgia-like Model in Female Rats

Though the mechanisms are not fully understood, tryptophan (Trp) and physical exercise seem to regulate mechanical hypersensitivity in fibromyalgia. Here, we tested the impact of Trp supplementation and continuous low-intensity aerobic exercise on the modulation of mechanical hypersensitivity in a fibromyalgia-like model induced by acid saline in female rats. Twelve-month-old female Wistar rats were randomly divided into groups: [control (n = 6); acid saline (n = 6); acid saline + exercise (n = 6); acid saline + Trp (n = 6); and acid saline + exercise + Trp (n = 6)]. Hypersensitivity was caused using two intramuscular jabs of acid saline (20 μL; pH 4.0; right gastrocnemius), 3 days apart. The tryptophan-supplemented diet contained 7.6 g/hg of Trp. The three-week exercise consisted of progressive (30-45 min) treadmill running at 50 to 60% intensity, five times (Monday to Friday) per week. We found that acid saline induced contralateral mechanical hypersensitivity without changing the levels of Trp, serotonin (5-HT), and kynurenine (KYN) in the brain. Hypersensitivity was reduced by exercise (~150%), Trp (~67%), and its combination (~160%). The Trp supplementation increased the levels of Trp and KYN in the brain, and the activity of indoleamine 2,3-dioxygenase (IDO), and decreased the ratio 5-HT:KYN. Exercise did not impact the assessed metabolites. Combining the treatments reduced neither hypersensitivity nor the levels of serotonin and Trp in the brain. In conclusion, mechanical hypersensitivity induced by acid saline in a fibromyalgia-like model in female rats is modulated by Trp supplementation, which increases IDO activity and leads to improved Trp metabolism via the KYN pathway. In contrast, physical exercise does not affect mechanical hypersensitivity through brain Trp metabolism via either the KYN or serotonin pathways. Because this is a short study, generalizing its findings warrants caution.

Exercise-Induced Central Fatigue: Biomarkers, and Non-Medicinal Interventions

Fatigue, commonly experienced in daily life, is a feeling of extreme tiredness, shortage or lack of energy, exhaustion, and difficulty in performing voluntary tasks. Central fatigue, defined as a progressive failure to voluntarily activate the muscle, is typically linked to moderate- or light-intensity exercise. However, in some instances, high-intensity exercise can also trigger the onset of central fatigue. Exercise-induced central fatigue often precedes the decline in physical performance in well-trained athletes. This leads to a reduction in nerve impulses, decreased neuronal excitability, and an imbalance in brain homeostasis, all of which can adversely impact an athlete's performance and the longevity of their sports career. Therefore, implementing strategies to delay the onset of exercise-induced central fatigue is vital for enhancing athletic performance and safeguarding athletes from the debilitating effects of fatigue. In this review, we discuss the structural basis, measurement methods, and biomarkers of exercise-induced central fatigue. Furthermore, we propose non-pharmacological interventions to mitigate its effects, which can potentially foster improvements in athletes' performances in a healthful and sustainable manner.

Continuous Aerobic Exercise Prevents Detrimental Remodeling and Right Heart Myocyte Contraction and Calcium Cycling Dysfunction in Pulmonary Artery Hypertension

ABSTRACT

Pulmonary artery hypertension (PAH) imposes right heart and lung detrimental remodeling which impairs cardiac contractility, physical effort tolerance, and survival. The effects of an early moderate-intensity continuous aerobic exercise training on the right ventricle and lung structure, and on contractility and the calcium (Ca2+) transient in isolated myocytes from rats with severe PAH induced by monocrotaline were analyzed. Rats were divided into control sedentary (CS), control exercise (CE), monocrotaline sedentary (MS), and monocrotaline exercise (ME) groups. Animals from control exercise and ME groups underwent a moderate-intensity aerobic exercise on a treadmill (60 min/d; 60% intensity) for 32 days, after a monocrotaline (60 mg/kg body weight i.p.) or saline injection. The pulmonary artery resistance was higher in MS than in control sedentary (1.36-fold) and was reduced by 39.39% in ME compared with MS. Compared with MS, the ME group presented reduced alveolus (17%) and blood vessel (46%) wall, fibrosis (25.37%) and type I collagen content (55.78%), and increased alveolus (52.96%) and blood vessel (146.97%) lumen. In the right ventricle, the ME group exhibited diminished hypertrophy index (25.53%) and type I collagen content (40.42%) and improved myocyte contraction [ie, reduced times to peak (29.27%) and to 50% relax (13.79%)] and intracellular Ca2+ transient [ie, decreased times to peak (16.06%) and to 50% decay (7.41%)] compared with MS. Thus, early moderate-intensity continuous aerobic exercise prevents detrimental remodeling in the right heart and lung increases in the pulmonary artery resistance and dysfunction in single myocyte contraction and Ca2+ cycling in this model.

Effect of a Moderate-Intensity Aerobic Training on Joint Biomarkers and Functional Adaptations in Rats Subjected to Induced Knee Osteoarthritis

Background

Knee osteoarthritis (_kOA) is a common chronic disease that induces changes in redox status and inflammatory biomarkers, cell death, and motor impairment. Aerobic training can be a non-pharmacological alternative to prevent the progression of the disease.

Objective

To evaluate the effects of an 8 weeks moderate-intensity treadmill aerobic training program on redox status and inflammatory biomarkers and motor performance in _kOA-like changes induced by monosodium iodoacetate (MIA) in rats.

Methods

Twenty-seven rats were randomly divided into three groups: SHAM; induced _kOA (OA); and induced _kOA + aerobic training (OAE). Motor performance was evaluated by the number of falls on rotarod test, the total time of displacement and the number of failures on a 100 cm footbridge. Data for cytokines and histology were investigated locally, whereas plasma was used for redox status biomarkers.

Results

The OA group, compared to the SHAM group, increased 1.13 times the total time of displacement, 6.05 times the number of failures, 2.40 times the number of falls. There was also an increase in cytokine and in thiobarbituric acid reactive substances (TBARS) (IL1β: 5.55-fold, TNF: 2.84-fold, IL10: 1.27-fold, IL6: 1.50-fold, TBARS: 1.14-fold), and a reduction of 6.83% in the total antioxidant capacity (FRAP), and of 35% in the number of chondrocytes. The aerobic training improved the motor performance in all joint function tests matching to SHAM scores. Also, it reduced inflammatory biomarkers and TBARS level at values close to those of the SHAM group, with no change in FRAP level. The number of falls was explained by IL1β and TNF (58%), and the number of failures and the total time of displacement were also explained by TNF (29 and 21%, respectively).

Conclusion

All findings indicate the efficacy of moderate-intensity aerobic training to regulate inflammatory biomarkers associated with improved motor performance in induced _kOA-like changes, thus preventing the loss of chondrocytes.

Mechanisms of sex differences in exercise capacity

Sex differences are an important component of National Institutes of Health rigor. The goal of this investigation was to test the hypothesis that female mice have greater exercise capacity than male mice, and that it is due to estrogen, nitric oxide, and myosin heavy chain expression. Female C57BL6/J wild-type mice exhibited greater (P < 0.05) maximal exercise capacity for running distance (489 ± 15 m) than age-matched male counterparts (318 ± 15 m), as well as 20% greater work to exhaustion. When matched for weight or muscle mass, females still maintained greater exercise capacity than males. Increased type I and decreased type II myosin heavy chain fibers in the soleus muscle from females are consistent with fatigue resistance and better endurance in females compared with males. After ovariectomy, female mice no longer demonstrated enhanced exercise, and treatment of male mice with estrogen resulted in exercise capacity similar to that of intact females (485 ± 37 m). Nitric oxide synthase, a downstream target of estrogen, exhibited higher activity in female mice compared with male mice, P < 0.05, whereas ovariectomized females exhibited nitric oxide synthase levels similar to males. Nitric oxide synthase activity also increased in males treated with chronic estrogen to levels of intact females. Nitric oxide synthase blockade with Nω-nitro-l-arginine methyl ester eliminated the sex differences in exercise capacity. Thus estrogen, nitric oxide, and myosin heavy chain expression are important mechanisms mediating the enhanced exercise performance in females.

Disruption of adenylyl cyclase type 5 mimics exercise training

Exercise training is key to healthful longevity. Since exercise training compliance is difficult, it would be useful to have a therapeutic substitute that mimicked exercise training. We compared the effects of exercise training in wild-type (WT) littermates with adenylyl cyclase type 5 knock out (AC5 KO) mice, a model of enhanced exercise performance. Exercise performance, measured by maximal distance and work to exhaustion, was increased in exercise-trained WT to levels already attained in untrained AC5 KO. Exercise training in AC5 KO further enhanced their exercise performance. The key difference in untrained AC5 KO and exercise-trained WT was the β-adrenergic receptor signaling, which was decreased in untrained AC5 KO compared to untrained WT but was increased in WT with exercise training. Despite this key difference, untrained AC5 KO and exercise-trained WT mice shared similar gene expression, determined by deep sequencing, in their gastrocnemius muscle with 183 genes commonly up or down-regulated, mainly involving muscle contraction, metabolism and mitochondrial function. The SIRT1/PGC-1α pathway partially mediated the enhanced exercise in both AC5 KO and exercise-trained WT mice, as reflected in the reduced exercise responses after administering a SIRT1 inhibitor, but did not abolish the enhanced exercise performance in the AC5 KO compared to untrained WT. Increasing oxidative stress with paraquat attenuated exercise performance more in untrained WT than untrained AC5 KO, reflecting the augmented oxidative stress protection in AC5 KO. Blocking nitric oxide actually reduced the enhanced exercise performance in untrained AC5 KO and trained WT to levels below untrained WT, demonstrating the importance of this mechanism. These results suggest that AC5 KO mice, without exercise training, share similar mechanisms responsible for enhanced exercise capacity with chronic exercise training, most importantly increased nitric oxide, and demonstrate more reserve with the addition of exercise training. A novel feature of the enhanced exercise performance in untrained AC5 KO mice is their decreased sympathetic tone, which is also beneficial to patients with cardiovascular disease.

Exercise training with concomitant nitric oxide synthase inhibition improved anxiogenic behavior, spatial cognition, and BDNF/P70S6 kinase activation in 20-month-old rats

This study aimed to investigate the effect of exercise and nitric oxide synthase (NOS) inhibition on memory, anxiety, and protein levels of brain-derived neurotrophic factor (BDNF) and P70S6 kinase (P70S6K). Twenty-month-old rats were divided into 6 groups: a control group, 2 groups treated with l-nitro-arginine methyl ester (L-NAME) (25 or 100 mg/kg) for 63 days, 2 groups treated with L-NAME (25 or 100 mg/kg) for 63 days plus 2 months of exercise, and 1 group treated with exercise. Behavioral tests were conducted to determine the anxiolytic and memory-improving role of exercise and NOS inhibition. BDNF, P70S6K, and cleaved caspase-3 protein levels in the hippocampus and prefrontal cortex were evaluated by Western blotting. Exercise and L-NAME (25 mg/kg) or their combination had an anxiolytic effect and improved spatial memory in old rats compared with the control or exercised group, respectively. Exercise and treatment with a low dose of L-NAME (25 mg/kg) each increased BDNF and P70S6K in the hippocampus and prefrontal cortex compared with levels in control rats. In comparison with exercise alone, co-treatment with exercise and a low dose of L-NAME (25 mg/kg) also increased BDNF and P70S6K in the hippocampus. The neuronal level of cleaved caspase-3 was reduced in the L-NAME (25 mg/kg) + exercise group compared with the exercised group. The L-NAME (100 mg/kg) + exercise treatment had no positive behavioral or molecular effects compared with exercise alone. The protective role of NOS inhibition and aerobic exercise against aging is probably modulated via BDNF and P70S6K in the brain.

Involvement of the TRPV1 channel in the modulation of spontaneous locomotor activity, physical performance and physical exercise-induced physiological responses

Physical exercise triggers coordinated physiological responses to meet the augmented metabolic demand of contracting muscles. To provide adequate responses, the brain must receive sensory information about the physiological status of peripheral tissues and organs, such as changes in osmolality, temperature and pH. Most of the receptors involved in these afferent pathways express ion channels, including transient receptor potential (TRP) channels, which are usually activated by more than one type of stimulus and are therefore considered polymodal receptors. Among these TRP channels, the TRPV1 channel (transient receptor potential vanilloid type 1 or capsaicin receptor) has well-documented functions in the modulation of pain sensation and thermoregulatory responses. However, the TRPV1 channel is also expressed in non-neural tissues, suggesting that this channel may perform a broad range of functions. In this review, we first present a brief overview of the available tools for studying the physiological roles of the TRPV1 channel. Then, we present the relationship between the TRPV1 channel and spontaneous locomotor activity, physical performance, and modulation of several physiological responses, including water and electrolyte balance, muscle hypertrophy, and metabolic, cardiovascular, gastrointestinal, and inflammatory responses. Altogether, the data presented herein indicate that the TPRV1 channel modulates many physiological functions other than nociception and thermoregulation. In addition, these data open new possibilities for investigating the role of this channel in the acute effects induced by a single bout of physical exercise and in the chronic effects induced by physical training.

ÓXIDO NÍTRICO E DINÂMICA DE CA2+ EM CARDIOMIÓCITOS: INFLUÊNCIA DA CAPACIDADE DE EXERCÍCIO

RESUMO Introdução: A capacidade intrínseca para o exercício aeróbico está relacionada com o inotropismo cardíaco. Por outro lado, a participação do óxido nítrico (NO) como mensageiro intracelular sobre a dinâmica do Ca2+ ainda permanece desconhecida em ratos com diferentes capacidades intrínsecas para o exercício. Objetivo: Avaliar se o NO modula diferentemente o transiente intracelular de Ca2+ e liberações espontâneas de Ca2+(sparks) em cardiomiócitos de ratos com diferentes capacidades intrínsecas para o exercício. Métodos: Ratos machos Wistar foram selecionados como desempenho padrão (DP) e alto desempenho (AD), de acordo com a capacidade de exercício até a fadiga, mensurada através de teste de esforço progressivo em esteira. Os cardiomiócitos dos ratos foram utilizados para determinar o transiente intracelular de Ca2+ e Ca2+sparks em microscópio confocal. Para estimar a contribuição do NO foi utilizado o inibidor das sínteses do NO (L-NAME, 100 µM). Os dados foram analisados através de ANOVA two-way seguido do pós-teste de Tukey e apresentados como médias ± EPM. Resultados: Os cardiomiócitos de ratos AD exibiram aumentos na amplitude do transiente de Ca2+ em comparação aos DP. Entretanto, o L-NAME aumentou a amplitude do transiente de Ca2+ somente em ratos DP. Não foram encontradas diferenças na constante de tempo de decaimento do transiente de Ca2+ (t) em cardiomiócitos de ratos com DP e AP, contudo, a administração do L-NAME diminuiu o t em cardiomiócitos em ambos os grupos. cardiomiócitos de ratos AD apresentaram menor amplitude e frequência de Ca2+sparks em comparação ao grupo DP. A administração de L-NAME aumentou a amplitude de Ca2+sparks em cardiomiócitos do grupo AD. Conclusão: O NO modula o transiente de Ca2+ e as sparks de Ca2+ em cardiomiócitos de ratos com diferentes capacidades intrínsecas para o exercício.

Endurance training upregulates the nitric oxide/soluble guanylyl cyclase/cyclic guanosine 3',5'-monophosphate pathway in the striatum, midbrain and cerebellum of male rats

The nitric oxide/soluble guanylyl cyclase/cyclic guanosine monophosphate (NO/sGC/cGMP) brain pathway plays an important role in motor control. We studied the effects of 6-week endurance training (running) of moderate intensity on this pathway by comparing, between sedentary and endurance-trained young adult male Wistar rats, the expression of endothelial (eNOS) and neuronal (nNOS) NO synthases and of α1, α2 and β1 GC subunits, as well as cGMP levels, in the brain cortex, hippocampus, striatum, midbrain and cerebellum. Additionally, we compared the respective regional expressions of BDNF and the BDNF receptor TrkB. Twenty-four hours after the last training session, the endurance-trained rats showed 3-fold higher spontaneous locomotor activity than their sedentary counterparts in an open-field test. Forty-eight hours after the completion of the training, the trained rats showed significantly elevated BDNF and TrKB mRNAs in the hippocampus, midbrain and striatum, and significantly increased BDNF levels in the hippocampus and striatum. Simultaneously, significant increases were found in mRNA and protein levels and activities of nNOS and eNOS as well as in mRNA and protein levels of GCα2 and GCβ1, but not GCα1, in the striatum, midbrain and cerebellum; no change in these variables was found in the cortex and hippocampus except for marked elevations in cortical GCβ1 mRNA and protein. Changes in regional cGMP levels paralleled those in eNOS, nNOS and GCα2 expression and NOSs' activities. These results suggest that favorable extrapyramidal motor effects of physical training are related to the enhanced activity of the NO/sGC/cGMP pathway in certain motor control-related subcortical brain regions.

The time of day differently influences fatigue and locomotor activity: is body temperature a key factor?

The aim of this study was to verify the possible interactions between exercise capacity and spontaneous locomotor activity (SLA) during the oscillation of core body temperature (Tb) that occurs during the light/dark cycle. Wistar rats (n=11) were kept at an animal facility under a light/dark cycle of 14/10h at an ambient temperature of 23°C and water and food ad libitum. Initially, in order to characterize the daily oscillation in SLA and Tb of the rats, these parameters were continuously recorded for 24h using an implantable telemetric sensor (G2 E-Mitter). The animals were randomly assigned to two progressive exercise test protocols until fatigue during the beginning of light and dark-phases. Fatigue was defined as the moment rats could not keep pace with the treadmill. We assessed the time to fatigue, workload and Tb changes induced by exercise. Each test was separated by 3days. Our results showed that exercise capacity and heat storage were higher during the light-phase (p<0.05). In contrast, we observed that both SLA and Tb were higher during the dark-phase (p<0.01). Notably, the correlation analysis between the amount of SLA and the running capacity observed at each phase of the daily cycle revealed that, regardless of the time of the day, both types of locomotor physical activity have an important inherent component (r=0.864 and r=0.784, respectively, p<0.01) without a direct relationship between them. This finding provides further support for the existence of specific control mechanisms for each type of physical activity. In conclusion, our data indicate that the relationship between the body temperature and different types of physical activity might be affected by the light/dark cycle. These results mean that, although exercise performance and spontaneous locomotor activity are not directly associated, both are strongly influenced by daily cycles of light and dark.

Behavioral and biochemical effects of a formulation of the traditional Chinese medicine, Kai-Xin-San, in fatigued rats

The present study was designed to evaluate the anti-fatigue activity and the behavioral and biochemical effects of Kai-Xin-San (KXS) extracts on fatigued rats. The rats were randomly divided into six groups: untreated control (UC), running control (RC), RC treated with 13 mg/kg/day modafinil and RC treated with KXS at dosages of 125, 250 and 500 mg/kg/day, respectively. The treatments were administered orally. Anti-fatigue activity was assessed using the treadmill running test and serum biochemical parameters were determined using an autoanalyzer and commercially available kits. Furthermore, the standardization of the KXS extracts was ensured using a high-performance liquid chromatography (HPLC)-fingerprint. The extracts were shown to increase exhaustive running time in the treadmill running test and reverse the fatigue-induced reduction in hepatic/muscle glycogen and testosterone, in addition to reducing the lactate dehydrogenase (LDH), serum urea nitrogen (SUN), blood lactic acid (BLA) and β-endorphin levels in the serum of the fatigued rats. Moreover, the extracts enhanced superoxide dismutase (SOD) activity and decreased the malondialdehyde (MDA) levels in the serum of the fatigued rats. The results of this preliminary study indicated that KXS exhibits anti-fatigue activity. This was reflected in the effects on the biochemical markers for fatigue.

Inhibition of phosphodiesterase-5 rescues age-related impairment of synaptic plasticity and memory

Aging is characterized by a progressive cognitive decline that leads to memory impairment. Because the cyclic nucleotide cascade is essential for the integrity of synaptic function and memory, and it is down-regulated during aging and in neurodegenerative disorders, we investigated whether an increase in cGMP levels might rescue age-related synaptic and memory deficits in mice. We demonstrated that acute perfusion with the phosphodiesterase-5 inhibitor sildenafil (50 nM) ameliorated long-term potentiation in hippocampal slices from 26-30-month-old mice. Moreover, chronic intraperitoneal injection of sildenafil (3mg/kg for 3 weeks) improved age-related spatial learning and reference memory as tested by the Morris Water Maze, and recognition memory as tested by the Object Recognition Test. Finally, sildenafil restored central cAMP responsive element-binding protein (CREB) phosphorylation, which is crucial for synaptic plasticity and memory. Our data suggest that inhibition of phosphodiesterase-5 may be beneficial to treat age-related cognitive dysfunction in a physiological mouse model of aging.

Differential effects of physical exercise and L-arginine on cortical spreading depression in developing rats

OBJECTIVE

We investigated the effect of early-in-life administration of L-arginine, combined with physical exercise, on cortical spreading depression (CSD) in young and adult rats.

METHODS

L-arginine (300 mg/kg/day, n = 40) or distilled water (vehicle, n = 40) was given to the rats during postnatal days 7-35 by gavage. Physical exercise (treadmill) was carried out during postnatal days 15-35 in half of the animals in each gavage condition described above. The other half (non-exercised) was used for comparison. When the animals reached 35-45 days (young groups) or 90-120 days of age (adult) CSD was recorded on two cortical points during 4 hours and CSD propagation velocity was calculated.

RESULTS

L-arginine-treated + exercised rats had increased body weight, but not brain weight, in adult age compared to L-arginine + non-exercised ones (P < 0.05). In both young and adult animals, L-arginine increased, whereas exercise decreased the CSD propagation velocity. Analysis of variance revealed a significant interaction between gavage treatment and age (P < 0.001), and also between gavage treatment and exercise (P = 0.004), but not between age and exercise. An additional control group of young rats, treated with 300 mg/kg of L-histidine, presented CSD velocities comparable to the corresponding water-treated controls, suggesting that the CSD acceleration seen in the L-arginine group was an L-arginine-specific effect, rather than an effect due to a non-specific amino acid imbalance.

DISCUSSION

L-arginine and exercise affect CSD differentially (L-arginine accelerated, while exercise decelerated CSD), and both effects did interact. Probably, they depend on developmental plasticity changes associated with the treatments.

Exercise training and detraining modify the morphological and mechanical properties of single cardiac myocytes obtained from spontaneously hypertensive rats

We determined the effects of exercise training and detraining on the morphological and mechanical properties of left ventricular myocytes in 4-month-old spontaneously hypertensive rats (SHR) randomly divided into the following groups: sedentary for 8 weeks (SED-8), sedentary for 12 weeks (SED-12), treadmill-running trained for 8 weeks (TRA, 16 m/min, 60 min/day, 5 days/week), and treadmill-running trained for 8 weeks followed by 4 weeks of detraining (DET). At sacrifice, left ventricular myocytes were isolated enzymatically, and resting cell length, width, and cell shortening after stimulation at a frequency of 1 Hz (~25°C) were measured. Cell length was greater in TRA than in SED-8 (161.30 ± 1.01 vs 156.10 ± 1.02 μm, P < 0.05, 667 vs 618 cells, respectively) and remained larger after detraining. Cell width and volume were unaffected by either exercise training or detraining. Cell length to width ratio was higher in TRA than in SED-8 (8.50 ± 0.08 vs 8.22 ± 0.10, P < 0.05) and was maintained after detraining. Exercise training did not affect cell shortening, which was unchanged with detraining. TRA cells exhibited higher maximum velocity of shortening than SED-8 (102.01 ± 4.50 vs 82.01 ± 5.30 μm/s, P < 0.05, 70 cells per group), with almost complete regression after detraining. The maximum velocity of relengthening was higher in TRA cells than in SED-8 (88.20 ± 4.01 vs70.01 ± 4.80 μm/s, P < 0.05), returning to sedentary values with detraining. Therefore, exercise training affected left ventricle remodeling in SHR towards eccentric hypertrophy, which remained after detraining. It also improved single left ventricular myocyte contractile function, which was reversed by detraining.

Effects of blockade of central dopamine D1 and D2 receptors on thermoregulation, metabolic rate and running performance

To assess the effects of a blockade of central D1- and D2-dopaminergic receptors on metabolic rate, heat balance and running performance, 10 nmol (2 microl) of a solution of the D(1) antagonist SCH-23390 hydrochloride (SCH, n = 6), D2 antagonist eticlopride hydrochloride (Eti, n = 6), or 2 microl of 0.15 M NaCl (SAL, n = 6) was injected intracerebroventricularly into Wistar rats before the animals began graded running until fatigue (starting at 10 m/min, increasing by 1 m/min increment every 3 min until fatigue, 5% inclination). Oxygen consumption and body temperature were recorded at rest, during exercise and following 30 min of recovery. Control experiments with injection of two doses (10 and 20 nmol/rat) of either SCH or Eti solution were carried out in resting rats as well. Body heating rate, heat storage, workload and mechanical efficiency were calculated. Although SCH and Eti treatments did not induce thermal effects in resting animals, they markedly reduced running performance (-83%, SCH; -59% Eti, p < 0.05) and decreased maximal oxygen uptake (-79%, SCH; -45%, Eti, p < 0.05) in running rats. In addition, these treatments induced a higher body heating rate and persistent hyperthermia during the recovery period. Our data demonstrate that the alteration in dopamine transmission induced by the central blockade of dopamine- D1 and D2 receptors impairs running performance by decreasing the tolerance to heat storage. This blockade also impairs the dissipation of exercise-induced heat and metabolic rate recovery during the post-exercise period. Our results provide evidence that central activation of either dopamine- D1 or D2 receptors is essential for heat balance and exercise performance.

Central angiotensin AT1 receptors are involved in metabolic adjustments in response to graded exercise in rats

To investigate the influence of central angiotensin AT1-receptors blockade on metabolic adjustments during graded exercise, Losartan (Los) was intracerebroventricularly injected in rats before running until fatigue. Oxygen consumption (VO2) was measured (n=6) and blood samples collected (n=7) to determine variations of glucose, lactate and free fatty acids (FFA). Los-rats exhibited a hyperglycemic response, already observed at 20% of maximal work, followed by a higher lactate levels and FFA mobilization from adipose tissue. Despite the reduced total time to fatigue and the higher VO2 associated with reduced mechanical efficiency, exercise led to the attainment of similar levels of effort in both groups. In summary, central AT1-receptor blockade during graded exercise induces hyperglycemia and higher FFA mobilization from adipose tissue at low exercise intensities in rats running at the same absolute exercise intensity. These data suggest that the central angiotensinergic system is involved in metabolic adjustments during exercise since central blockade of AT1-receptors shifts energy balance during graded exercise, similarly to situations of higher and premature sympathetic activation.

Exercise capacity is related to calcium transients in ventricular cardiomyocytes

The aim of the present study was to evaluate the Ca2+ handling and contractility properties of cardiomyocytes isolated from rats with high intrinsic aerobic exercise capacity. Standard-performance (SP) and high-performance (HP) rats were categorized with a treadmill progressive exercise test according to the exercise time to fatigue (TTF). The SP group included rats with TTF between 16.63 and 46.57 min, and the HP group included rats with TTF >46.57 min. Isolated ventricular cardiomyocytes were dissociated from the hearts of SP and HP rats, and intracellular global Ca2+ ([Ca2+]i) transients were measured. The [Ca2+]i transient peak was increased in the HP group relative to the SP group (5.54 ± 0.31 vs. 4.18 ± 0.12 F/F0; P ≤ 0.05) and was positively correlated with the TTF attained during the progressive test ( r = 0.81). We also performed contractility measurements in isolated cardiomyocytes and found higher amplitude of contraction in the HP group compared with the SP group (6.7 ± 0.2 vs. 6.0 ± 0.3% resting cell length; P ≤ 0.05). To reinforce the intrinsic differences between SP and HP rats, we performed Western blot experiments and observed increased expression of sarco(endo)plasmic reticulum Ca2+-ATPase type 2a (1.30 ± 0.07 vs. 1.74 ± 0.18 arbitrary units; P ≤ 0.05) and ryanodine receptor type 2 (1.86 ± 0.13 vs. 3.57 ± 0.12 arbitrary units; P ≤ 0.05) in HP rats. In summary, our data showed important intrinsic differences in cardiomyocyte properties that could explain some of the divergence observed in rats with high intrinsic aerobic exercise capacity.

Performance-enhancing and thermoregulatory effects of intracerebroventricular dopamine in running rats

To assess the role of central dopamine on metabolic rate, heat balance and running performance, 2.0 microL of 5 x 10(-3)M dopamine solution (DA) or 0.15M NaCl (SAL) was intracerebroventricularly injected in Wistar rats 1 min before running on a motor-driven treadmill, according to a graded exercise protocol, until fatigue. Oxygen consumption (VO(2)) and body temperature (T(b)) were recorded at rest, during exercise, and after 30 min of recovery. DA induced a marked increase in workload (approximately 45%, p<0.05). At fatigue point, DA-injected rats attained approximately 29% higher maximum oxygen consumption (VO(2max)) and approximately 0.75 degrees C higher T(b) than SAL-injected rats. Despite the higher VO(2max) and T(b) attained during exercise, DA-treated rats reached VO(2) basal values within the same recovery period and dissipated heat approximately 33% faster than SAL-treated rats (p<0.05). The mechanical efficiency loss rate was approximately 40% lower in DA than in SAL-treated rats (p<0.05), however, the heat storage was approximately 35% higher in the DA group (p<0.05). Our results demonstrate that increased DA availability in the brain has a performance-enhancing effect, which is mediated by improvements in the tolerance to heat storage and increases in the metabolic rate induced by graded exercise. These data provide further evidence that central activation of dopaminergic pathways plays an important role in exercise performance.

Central AT(1) receptor blockade increases metabolic cost during exercise reducing mechanical efficiency and running performance in rats

The effect of central angiotensin AT(1) receptor blockade on metabolic rate and running performance in rats during exercise on a treadmill (18 m x min(-1), 5% inclination) was investigated. Oxygen consumption (VO(2)) was measured, using the indirect calorimetry system, while the animals were exercising until fatigue after injection of 2 microL of losartan (Los; 60 nmol, n=9), an angiotensin II AT(1) receptor antagonist, or 2 microL of 0.15 M NaCl (Sal, n=9) into the right lateral cerebral ventricle. Mechanical efficiency (ME) and workload (W) were calculated. The W performance by Los-treated animals was 29% lesser than in Sal-treated animals (p<0.02). During the first 10 min of exercise (dynamic state of exercise), there was a similar increase in VO(2), while ME remained the same in both groups. Thereafter (steady state of exercise), VO(2) remained stable in the Sal group but continued to increase and stabilized at a higher level in Los-treated animals until fatigue. During the steady state of exercise there was a sharper reduction in ME in Los-treated rats compared to Sal-treated animals (p<0.01) that was closely correlated to W (r=0.74; p<0.01). Our data showed that AT(1) receptor blockade increases metabolic cost during exercise, reducing mechanical efficiency. These results indicate that central angiotensinergic transmission modulates heat production, improving ME during the steady state of exercise.

Tryptophan-induced central fatigue in exercising rats is related to serotonin content in preoptic area

To assess the effects of increased hypothalamic tryptophan (TRP) availability on 5-HT content in preoptic area on thermoregulation and work production during exercise on treadmill, 20.3 microM of L-TRP (n=7) or 0.15M NaCl (n=6) was injected into the lateral cerebral ventricle of male Wistar rats immediately before the animals started running (18 m min(-1) 5% inclination). Exercise time to fatigue (min), and workload (kgm) were analysed. Core temperature was measured by telemetry. At fatigue, brains were quickly removed and preoptic area (POA), hypothalamus (HP), frontal cortex (FC), hippocampi (HC) were rapidly dissected and frozen immediately in dry ice. Serotonin (5-HT) and 5-hydroxyindoleacetic acid (5-HIAA) were measured by HPLC. TRP-exercised rats showed the highest content of 5-HT in the POA and the lowest in the hippocampi compared to the rested and SAL-exercised rats. An inverse relationship between TF and a direct correlation with body temperature changes and POA-5HT levels were observed. A correlation between HC 5-HT content and TF was also found. However, there was no correlation between HC 5-HT content and changes in Tb at fatigue. Finally, our results bring further evidences that increased 5-HT content in POA is involved with an increase in heat production during exercise. In addition, the direct correlation of 5-HT level in hippocampi and TF of TRP-exercised rats suggests that this brain area is also related to motor activity control during exercise. In conclusion, our data indicated that tryptophan-induced central fatigue in exercising rats is related to serotonin content in preoptic area.