Determination of anaerobic threshold in rats using the lactate minimum test

Swimming training prevents obesity installation and normalizes hypothalamic expressions of GLP1 and leptin receptors in adult offspring born in small litters

OBJECTIVE

Glucagon-like peptide-1 (GLP1) and leptin (Lep) are afferent signals that regulate energy metabolism. Lactational hypernutrition results in hyperphagia and adiposity in adult life, and these events can be prevented by exercise. We evaluated the effects of swimming training on hypothalamic (GLP1-R) and Lep receptor (Lep-R) gene expressions in lactational hypernutrition-induced obesity.

METHODS

On the 3rd postnatal day, the litter sizes of lactating dams were adjusted to small litters (SL; 3 pups/dams) or normal litters (NL; 9 pups/dams). After weaning (21 days), NL and SL male rats were randomly distributed to sedentary (Sed) and exercised (Exe) groups. Exercised mice swam (30 min/3 times/week) for 68 days. Food intake and body weight gain were registered. At 92 days, intraperitoneal glucose and insulin tolerance tests were performed and rats were euthanized at 93 days; adipose tissue depots were weighed, and blood counts and plasma biochemical analyses performed. Hypothalamus were isolated to evaluate Lep-R and GLP1-R gene expressions.

RESULTS

Small litters sedentary rats presented increased body weight gain, adiposity, insulin sensibility and higher fasting values of glucose and triglycerides, besides higher hypothalamic gene expressions of Lep-R and GLP1-R, compared to NLSed animals. SLExe rats did not develop obesity or metabolic abnormalities and Lep-R and GLP1-R hypothalamic gene expressions were normalized.

CONCLUSION

Lactational hypernutrition induces obesity and metabolic dysfunction in adult life, in association with higher hypothalamic expressions of the Lep-R and GLP1-R genes. Exercise prevented obesity and improved metabolic state in SL overnourished rats, and normalized their hypothalamic Lep-R and GLP1-R gene expressions.

The Impact of Chronic Stress on Behavior and Body Mass in New Animal Models

(1) Background: Exposure to different sources of stress can have a significant effect on both psychological and physical processes. (2) Methods: The study took place over a period of 34 days and included a total of 40 animals. Regarding the exposure to chronic stressors, we opted for physiological, non-invasive stressors, e.g., running, swimming, and changes in the intensity of light. An unforeseen stress batch was also created that alternated all these stress factors. The animals were divided into five experimental groups, each consisting of eight individuals. In the context of conducting the open field test for behavioral assessment before and after stress exposure, we aimed to investigate the impact of stress exposure on the affective traits of the animals. We also monitored body mass every two days. (3) Results: The control group exhibited an average increase in weight of approximately 30%. The groups exposed to stress factors showed slower growth rates, the lowest being the running group, recording a rate of 20.55%, and the unpredictable stress group at 24.02%. The anxious behavior intensified in the group with unforeseen stress, in the one with light variations, and in the running group. (4) Conclusions: Our research validates the animal model of intermittent light exposure during the dark phase as a novel method of inducing stress. The modification of some anxiety parameters was observed; they vary according to the type of stress. Body mass was found to increase in all groups, especially in the sedentary groups, likely due to the absence of cognitive, spatial, and social stimuli except for cohabitation.

A systematic review of exercise protocols applied to athymic mice in tumor-related experiments

Athymic mice are unable to produce T-cells and are then characterized as immunodeficient. This characteristic makes these animals ideal for tumor biology and xenograft research. New non-pharmacological therapeutics are required owing to the exponential increase in global oncology costs over the last 10 years and the high cancer mortality rate. In this sense, physical exercise is regarded as a relevant component of cancer treatment. However, the scientific community lacks information regarding the effect of manipulating training variables on cancer in humans, and experiments with athymic mice. Therefore, this systematic review aimed to address the exercise protocols used in tumor-related experiments using athymic mice. The PubMed, Web of Science, and Scopus databases were searched without restrictions on published data. A combination of key terms such as athymic mice, nude mice, physical activity, physical exercise, and training was used. The database search retrieved 852 studies (PubMed, 245; Web of Science, 390; and Scopus, 217). After title, abstract, and full-text screening, 10 articles were eligible. Based on the included studies, this report highlights the considerable divergences in the training variables adopted for this animal model. No studies have reported the determination of a physiological marker for intensity individualization. Future studies are recommended to explore whether invasive procedures can result in pathogenic infections in athymic mice. Moreover, time-consuming tests cannot be applied to experiments with specific characteristics such as tumor implantation. In summary, non-invasive, low-cost, and time-saving approaches can suppress these limitations and improve the welfare of these animals during experiments.

Effect of Type and Dose of Exercise on Neuropathic Pain After Experimental Sciatic Nerve Injury: A Preclinical Systematic Review and Meta-Analysis

This preclinical systematic review aimed to determine the effectiveness of different types and doses of exercise on pain behavior and biomarkers in preclinical models of focal neuropathic pain. We searched MEDLINE, EMBASE, Web of Science, PubMed, SCOPUS, CINAHL, and Cochrane library from inception to November 2022 for preclinical studies evaluating the effect of exercise compared to control interventions on neuropathic pain behavior after experimental sciatic nerve injury. If possible, data were meta-analyzed using random effect models with inverse-variance weighting. Thirty-seven studies were included and 26 meta-analyzed. Risk of bias (SYRCLE tool) remained unclear in most studies and reporting quality (CAMARADES) was variable. Exercise reduced mechanical (standardized mean differences [SMD] .53 (95% CI .31, .74), P = .0001, I2 = 0%, n = 364), heat (.32 (.07, .57), P = .01, I2 = 0%, n = 266) and cold hypersensitivity (.51 (.03, 1.0), P = .04, I2 = 0%, n = 90) compared to control interventions. No relationship was apparent between exercise duration or intensity and antinociception. Exercise modulated biomarkers related to different systems (eg, immune system, neurotrophins). Whereas firm conclusions are prevented by the use of male animals only, variable reporting quality and unclear risk of bias in many studies, our results suggest that aerobic exercise is a promising tool in the management of focal neuropathic pain. PERSPECTIVE: This systematic review and meta-analysis demonstrates that aerobic exercise reduces neuropathic pain-related behavior in preclinical models of sciatic nerve injury. This effect is accompanied by changes in biomarkers associated with inflammation and neurotrophins among others. These results could help to develop exercise interventions for patients with neuropathic pain.

Impact of lifestyle interventions targeting physical exercise and caloric intake on cirrhosis regression in rats

In patients, advanced cirrhosis only regresses partially once the etiological agent is withdrawn. Animal models for advanced cirrhosis regression are missing. Lifestyle interventions (LIs) have been shown to improve steatosis, inflammation, fibrosis, and portal pressure (PP) in liver disease. We aimed at characterizing cirrhosis regression after etiological agent removal in experimental models of advanced cirrhosis and to study the impact of different LI on it. Advanced cirrhosis was induced in rats either by carbon tetrachloride (CCl4) or by thioacetamide (TAA) administration. Systemic and hepatic hemodynamics, liver fibrosis, hepatic stellate cell (HSC) activation, hepatic macrophage infiltration, and metabolic profile were evaluated after 48 h, 4 wk or 8 wk of etiological agent removal. The impact of LI consisting in caloric restriction (CR) or moderate endurance exercise (MEE) during the 8-wk regression process was analyzed. The effect of MEE was also evaluated in early cirrhotic and in healthy rats. A significant reduction in portal pressure (PP), liver fibrosis, and HSC activation was observed during regression. However, these parameters remained above those in healthy animals. During regression, animals markedly worsened their metabolic profile. CR although preventing those metabolic disturbances did not further reduce PP, hepatic fibrosis, or HSC activation. MEE also prevented metabolic disturbances, without enhancing, but even attenuating the reduction of PP, hepatic fibrosis, and HSC activation achieved by regression. MEE also worsened hepatic fibrosis in early-TAA cirrhosis and in healthy rats.NEW & NOTEWORTHY We have developed two advanced cirrhosis regression experimental models with persistent relevant fibrosis and portal hypertension and an associated deteriorated metabolism that mimic what happens in patients. LI, despite improving metabolism, did not enhance the regression process in our cirrhotic models. CR did not further reduce PP, hepatic fibrosis, or HSC activation. MEE exhibited a profibrogenic effect in the liver blunting cirrhosis regression. One of the potential explanations of this worsening could be ammonia accumulation.

SHORT-TERM HIIT DOES NOT PROMOTE OXIDATIVE STRESS OR MUSCLE DAMAGE

ABSTRACT Introduction: High intensity interval training (HIIT) is a method that is widely used today. Objective: The present study aimed to evaluate the effects of HIIT on markers of oxidative stress and muscle damage in rats. Methods: The sample consisted of 60-day-old Wistar rats, divided into two groups: a control group (n=8) and an HIIT group (n=8). The training consisted of fourteen 20-second swimming sessions (loaded with weights equivalent to 14% of their body weight) with 10-second intervals between each session, performed for 12 consecutive days. Results: HIIT induced a reduction (−17.75%) in thiobarbituric acid reactive substances (an oxidative stress marker) in hepatic tissue (p=0.0482). There was also a reduction (−31.80%) in the HIIT group in the level of superoxide dismutase enzyme activity in the liver (p=0.0375). However, there were no differences between the groups in catalase, glutathione peroxidase, glutathione reductase, the total content of SH sulfhydryls, hydroperoxides, or carbonylated proteins in the hepatic tissue. No significant differences were found in any of these markers in the gastrocnemius muscle. The muscle damage markers creatinine kinase and lactate dehydrogenase were also similar between the groups in the gastrocnemius. Conclusion: The conclusion was that that short-term HIIT does not cause oxidative stress or muscle damage. Level of evidence I; High-quality randomized clinical trial with or without statistically significant difference, but with narrow confidence intervals.

Neurobiological effects of forced swim exercise on the rodent hippocampus: a systematic review

Forced swimming is a common exercise method used for its low cost and easy management, as seen in studies with the hippocampus. Since it is applied for varied research purposes many protocols are available with diverse aspects of physical intensity, time and periodicity, which produces variable outcomes. In the present study, we performed a systematic review to stress the neurobiological effects of forced swim exercise on the rodent hippocampus. Behavior, antioxidant levels, neurotrophins and inflammatory markers were the main topics examined upon the swimming effects. Better results among these analyses were associated with forced exercise at moderate intensity with an adaptation period and the opposite for continuous exhausting exercises with no adaptation. On further consideration, a standard swimming protocol is necessary to reduce variability of results for each scenario investigated about the impact of the forced swimming on the hippocampus.

Forced swimming is a common exercise method used for its low cost and easy management, as seen in studies with the hippocampus. Since it is applied for varied research purposes many protocols are available with diverse aspects of physical intensity, time and periodicity, which produces variable outcomes. In the present study, we performed a systematic review to stress the neurobiological effects of forced swim exercise on the rodent hippocampus. Behavior, antioxidant levels, neurotrophins and inflammatory markers were the main topics examined upon the swimming effects. Better results among these analyses were associated with forced exercise at moderate intensity with an adaptation period and the opposite for continuous exhausting exercises with no adaptation. On further consideration, a standard swimming protocol is necessary to reduce variability of results for each scenario investigated about the impact of the forced swimming on the hippocampus.

Ultra-Endurance Associated With Moderate Exercise in Rats Induces Cerebellar Oxidative Stress and Impairs Reactive GFAP Isoform Profile

Ultra-endurance (UE) race has been associated with brain metabolic changes, but it is still unknown which regions are vulnerable. This study investigated whether high-volume training in rodents, even under moderate intensity, can induce cerebellar oxidative and inflammatory status. Forty-five adult rats were divided into six groups according to a training period, followed or not by an exhaustion test (ET) that simulated UE: control (C), control + ET (C-ET), moderate-volume (MV) training and MV-ET, high-volume training (HV) and HV-ET. The training period was 30 (MV) and 90 (HV) min/day, 5 times/week for 3 months as a continuous running on a treadmill at a maximum velocity of 12 m/min. After 24 h, the ET was performed at 50% maximum velocities up to the animals refused to run, and then serum lactate levels were evaluated. Serum and cerebellar homogenates were obtained 24 h after ET. Serum creatine kinase (CK), lactate dehydrogenase (LDH), and corticosterone levels were assessed. Lipid peroxidation (LP), nitric oxide (NO), Interleukin 1β (IL-1β), and GFAP proteins, reduced and oxidized glutathione (GSH and GSSG) levels, superoxide dismutase (SOD) and catalase (CAT) activities were quantified in the cerebellum. Serum lactate concentrations were lower in MV-ET (∼20%) and HV-ET (∼40%) compared to the C-ET group. CK and corticosterone levels were increased more than ∼ twofold by HV training compared to control. ET increased CK levels in MV-ET vs. MV group (P = 0.026). HV induced higher LP levels (∼40%), but an additive effect of ET was only seen in the MV-ET group (P = 0.02). SOD activity was higher in all trained groups vs. C and C-ET (P < 0.05). CAT activity, however, was intensified only in the MV group (P < 0.02). The 50 kDa GFAP levels were enhanced in C-ET and MV-ET vs. respective controls, while 42 kDa (∼40%) and 39 kDa (∼26%) isoform levels were reduced. In the HV-ET group, the 50 KDa isoform amount was reduced ∼40-60% compared to the other groups and the 39 KDa isoform, increased sevenfold. LDH levels, GSH/GSSG ratio, and NO production were not modified. ET elevated IL-1β levels in the CT and MV groups. Data shows that cerebellar resilience to oxidative damage may be maintained under moderate-volume training, but it is reduced by UE running. High-volume training per se provoked systemic metabolic changes, cerebellar lipid peroxidation, and unbalanced enzymatic antioxidant resource. UE after high-volume training modified the GFAP isoform profile suggesting impaired astrocyte reactivity in the cerebellum.

Paracetamol-induced metabolic and cardiovascular changes are prevented by exercise training

Paracetamol (PAR) is the most frequently consumed non-prescription drug, yet it is well known to induce toxicity. Here, we have evaluated the effects of exercise training on vascular dysfunction induced by PAR. Rats were distributed among four groups: (a) Sedentary; (b) Exercise; (c) Sedentary+PAR; and (d) Exercise+PAR. The exercise comprised swimming 50 min/d, 5 d/wk for 6 weeks (+PAR in the last 2 weeks, at 400 mg/kg/d/p.o.). After killing, the rats' blood and aortas were collected for biochemical analysis of hepatic transaminases, TBARs reaction, glutathione, glutathione reductase, SOD, and catalase. In vitro vascular relaxation was measured using acetylcholine and sodium nitroprusside in the presence or absence of tiron (an antioxidant). Vascular protein expression (eNOS and sGC) also were analysed. Increased transaminases after PAR treatment were found to be reduced by exercise. Vasodilation was impaired by PAR only in the sedentary group. Exercise prevented alterations in lipoperoxidation and glutathione levels after PAR exposure. Glutaathione reductase and SOD also were increased by PAR but were normalized in the exercised group. Catalase activity and protein expressions did not change in any group. PAR treatment caused impairment in both vasodilation and redox balance; however, exercise training prevented the vascular and redox system dysfunction induced by PAR treatment.

Fitness is improved by adjustments in muscle intracellular signaling in rats with renovascular hypertension 2K1C undergoing voluntary physical exercise

AIM

To evaluate physical fitness and cardiovascular effects in rats with renovascular hypertension, two kidneys, one clip (2K1C) submitted to voluntary exercise (ExV).

MAIN METHODS

24 h after surgery (SHAM and 2K1C) rats were submitted to ExV for one week (adaptation). ExV adherent rats were separated into exercise (2K1C-EX and SHAM-EX) or sedentary (2K1C-SED and SHAM-SED) groups. After 4 weeks, exhaustion test, plasma lactate, cardiovascular parameters were evaluated and gastrocnemius muscle was removed for evaluation of gene expression of muscle metabolism markers (PGC1α; AMPK, SIRT-1, UCP-3; MCP-1; LDH) and of the redox process.

KEY FINDINGS

ExV decreased blood lactate concentration and increased SOD and CAT activity and a SIRT-1 and UCP-3 gene expression in the gastrocnemius muscle of 2K1C-ExV rats compared to 2K1C-SED rats. Gene expressions of PGC1α, UCP-3, MCT-1, AMPK were higher in 2K1C-ExV rats compared to SHAM-SED rats. Blood pressure in 2K1C-ExV was lower compared to 2K1C-SED and higher in SHAM-SED rats. Reflex bradycardia in 2K1C-EX rats increased compared to 2K1C-SED and was similar to SHAM-SED. The variation in mean blood pressure induced by ganglion blocker hexamethonium and Ang II AT1 receptor antagonist, losartan in the 2K1C-ExV rats was smaller compared to the 2K1C-SED rats and it was similar to the SHAM-SED rats.

SIGNIFICANCE

O ExV induced adaptive responses in 2K1C-ExV rats by decreasing sympathetic and Ang II activities and stimulating intracellular signaling that favors redox balance and reduced blood lactate concentration. These adaptive responses, then, contribute to reduced arterial pressure, improved baroreflex sensitivity and physical fitness of 2K1C rats.

Lifetime overproduction of circulating angiotensin-(1-7) in rats attenuates the increase in skeletal muscle damage biomarkers after exhaustive exercise

Angiotensin-(1-7) (Ang-[1-7]) can modulate glucose metabolism and protect against muscular damage. The aim of this study was to investigate the influence of lifetime increase of circulating levels of Ang-(1-7) at exhaustive swimming exercise (ESE). Sprague-Dawley (SD) and transgenic rats TGR(A1-7)3292 (TR) which overproduce Ang-(1-7) (2.5-fold increase) were submitted to ESE. The data showed no differences in time to exhaustion (SD: 4.90 ± 1.37 h vs. TR: 5.15 ± 1.15 h), creatine kinase, and transforming growth factor beta (TGF-β). Lactate dehydrogenase (SD: 219.9 ± 12.04 U/L vs. TR: 143.9 ± 35.21 U/L) and α-actinin (SD: 336.7 ± 104.5 U/L vs. TR: 224.6 ± 82.45 U/L) values were significantly lower in TR. There was a significant decrease in the range of blood glucose levels (SD: -41.4 ± 28.32 mg/dl vs. TR: -13.08 ± 39.63 mg/dl) in SD rats. Muscle (SD: 0.06 ± 0.02 mg/g vs. TR: 0.13 ± 0.01 mg/g) and hepatic glycogen (SD: 0.66 ± 0.36 mg/g vs. TG: 2.24 ± 1.85 mg/g) in TR were higher. The TR presented attenuation of the increase in skeletal muscle damage biomarkers and of the changes in glucose metabolism after ESE.

Acute exercise inhibits gastric emptying of liquids in rats: influence of the NO-cGMP pathway

We previously found that acute exercise inhibited the gastric emptying of liquid in awake rats by causing an acid-base imbalance. In the present study, we investigated the involvement of the nitric oxide-cyclic guanosine monophosphate (NO-cGMP) pathway, vasoactive intestinal peptide (VIP), and corticotropin-releasing factor (CRF) peptide in this phenomenon. Male rats were divided into exercise or sedentary group and were subjected to a 15-min swim session against a load (2.5 or 5% b.w.). The rate of gastric emptying was evaluated after 5, 10, or 20 min postprandially. Separate groups of rats were treated with vehicle (0.9% NaCl, 0.1 mL/100 g, ip) or one of the following agents: atropine (1.0 mg/kg, ip), the NO non-selective inhibitor Nω-nitro-L-arginine methyl ester hydrochloride (L-NAME; 10.0 mg/kg, ip), or the selective cGMP inhibitor 1H-(1,2,4)oxadiazole[4,3-a]quinoxalin-1-one (ODQ; 5.0 mg/kg, ip), the i-NOS non-specific inhibitor (aminoguanidine; 10.0 mg/kg, ip), the corticotropin-releasing factor receptor antagonist (astressin; 100 µg/kg, ip), or the vasoactive intestinal peptide (VIP) receptor antagonist Lys¹, Pro^2,5, Arg^3,4, Tyr⁶ (100 µg/kg, ip). Compared to sedentary rats, both the 2.5 and 5% exercise groups exhibited higher (P<0.05) values of blood lactate and fractional gastric dye recovery. Corticosterone and NO levels increased (P<0.05) in the 5% exercised rats. Pretreatment with astressin, VIP antagonist, atropine, L-NAME, and ODQ prevented the increase in gastric retention caused by exercise in rats. Acute exercise increased gastric retention, a phenomenon that appears to be mediated by the NO-cGMP pathway, CRF, and VIP receptors.

Chronic Swimming Exercise Ameliorates Low-Soybean-Oil Diet-Induced Spatial Memory Impairment by Enhancing BDNF-Mediated Synaptic Potentiation in Developing Spontaneously Hypertensive Rats

Exercise and low-fat diets are common lifestyle modifications used for the treatment of hypertension besides drug therapy. However, unrestrained low-fat diets may result in deficiencies of low-unsaturated fatty acids and carry contingent risks of delaying neurodevelopment. While aerobic exercise shows positive neuroprotective effects, it is still unclear whether exercise could alleviate the impairment of neurodevelopment that may be induced by certain low-fat diets. In this research, developing spontaneously hypertensive rats (SHR) were treated with chronic swimming exercise and/or a low-soybean-oil diet for 6 weeks. We found that performance in the Morris water maze was reduced and long-term potentiation in the hippocampus was suppressed by the diet, while a combination treatment of exercise and diet alleviated the impairment induced by the specific low-fat diet. Moreover, the combination treatment effectively increased the expression of brain-derived neurotrophic factor (BDNF) and N-methyl-D-aspartic acid receptor (NMDAR), which were both down-regulated by the low-soybean-oil diet in the hippocampus of developing SHR. These findings suggest that chronic swimming exercise can ameliorate the low-soybean-oil diet-induced learning and memory impairment in developing SHR through the up-regulation of BDNF and NMDAR expression.

Acute exercise alters homocysteine plasma concentration in an intensity-dependent manner due increased methyl flux in liver of rats

PURPOSE

We aimed to determine the effects of different intensities of acute exercise on Hcy plasma levels, and the exercise-induced changes in Hcy liver metabolism.

METHOD

First, thirty-two Wistar rats were randomly submitted to an acute bout of swimming exercise carrying a load of 2% (n=8), 4% (n=8) and 6% (n=8) of their total body weight attached in their tail. Control rats remained rested (n=8). Blood samples were taken from tail vein for plasma S-containing amino acids determination before (Rest) and post, 1, 2, 3, 4, 6, and 10h after acute swimming exercise. Second, 56 exercised rats (4% loads) were euthanized before (Rest) and1, 2, 3, 4, 6, and 10h after acute swimming exercise. Blood and liver samples were collected for amino acids and keys genes involved in the Hcy metabolism assay.

RESULTS

Acute exercise increases (P<0.05) plasma Hcy concentration in an intensity-dependent manner (rest 7.7±0.8; 6% load 13.8±3.6; 4% load 12.2±2.9±and 2% load 10.1±2.6, μmol/L); this increase is transient and does not promote hyperhomocysteinemia (<15μmol/L).Exercise-induced increased plasma Hcywas accompanied by the decreased liver S-adenosylmethionine/S-adenosylhomocysteine ratio and elevated MAT1a mRNA content. Acute exercise also caused elevated mRNA of key enzymes of transsulfuration (CBS) and remethylation (BHMT and the MTRR).

CONCLUSION

Our data provided evidence that acute exercise increases plasma Hcy concentration due to the augmented requirement for methylated compounds that increases liver SAM consumption. Also, Hcy remethylation and transsulfuration are coordinately regulated to maintain methyl balance.

Swimming exercise reverses CUMS-induced changes in depression-like behaviors and hippocampal plasticity-related proteins

BACKGROUND

Stress-induced failed resilience of brain plasticity can contribute to the onset and recurrence of depression. Chronic stress has been reported to open windows of epigenetic plasticity in hippocampus. However, how hippocampal plasticity underlies depression-like behaviors and how it adapts in response to stress has not been addressed. The present study aimed to investigate the signaling mechanisms of CUMS affecting hippocampal plasticity-related proteins expression and the regulation of swimming exercise in mice.

METHODS

Male C57BL/6 mice were subjected to chronic unpredictable mild stress (CUMS) for 7 weeks. From the 4th week, CUMS mice were trained in a moderate swimming program for a total of 4 weeks. A videocomputerized tracking system was used to record behaviors of animals for a 5-min session. Real-time PCR and Western Blotting were used to examine gene expression in mouse hippocampus.

RESULTS

Our results demonstrated that CUMS induced depression-like behaviors, which were reversed by swimming exercise. Moreover, the behavioral changes induced by CUMS and exercise were correlated with hippocampal plasticity-related proteins expression of growth-associated protein-43 (GAP-43) and synaptophysin (SYN). The molecular mechanisms regulating this plasticity may include SIRT1/mircoRNA, CREB/BDNF, and AKT/GSK-3β signaling pathways.

LIMITATIONS

We did not establish a correlation between depression-like behaviors induced by chronic stress and epigenetic changes of hippocampal plasticity, either a causal molecular signaling underling this plasticity.

CONCLUSIONS

Our findings have identified swimming exercise effects on CUMS-induced changes in depression-like behaviors and hippocampal plasticity-related proteins, which provide a framework for developing new strategies to treat stress-induced depression.

The Lactate Minimum Test: Concept, Methodological Aspects and Insights for Future Investigations in Human and Animal Models

In 1993, Uwe Tegtbur proposed a useful physiological protocol named the lactate minimum test (LMT). This test consists of three distinct phases. Firstly, subjects must perform high intensity efforts to induce hyperlactatemia (phase 1). Subsequently, 8 min of recovery are allowed for transposition of lactate from myocytes (for instance) to the bloodstream (phase 2). Right after the recovery, subjects are submitted to an incremental test until exhaustion (phase 3). The blood lactate concentration is expected to fall during the first stages of the incremental test and as the intensity increases in subsequent stages, to rise again forming a “U” shaped blood lactate kinetic. The minimum point of this curve, named the lactate minimum intensity (LMI), provides an estimation of the intensity that represents the balance between the appearance and clearance of arterial blood lactate, known as the maximal lactate steady state intensity (iMLSS). Furthermore, in addition to the iMLSS estimation, studies have also determined anaerobic parameters (e.g., peak, mean, and minimum force/power) during phase 1 and also the maximum oxygen consumption in phase 3; therefore, the LMT is considered a robust physiological protocol. Although, encouraging reports have been published in both human and animal models, there are still some controversies regarding three main factors: (1) the influence of methodological aspects on the LMT parameters; (2) LMT effectiveness for monitoring training effects; and (3) the LMI as a valid iMLSS estimator. Therefore, the aim of this review is to provide a balanced discussion between scientific evidence of the aforementioned issues, and insights for future investigations are suggested. In summary, further analyses is necessary to determine whether these factors are worthy, since the LMT is relevant in several contexts of health sciences.

Long-term treatment with Nandrolone Decanoate impairs mesenteric vascular relaxation in both sedentary and exercised female rats

Nandrolone Decanoate (ND) is an Anabolic Androgenic Steroid (AAS) that under abusive regimen can lead to multiple physiological adverse effects. Studies of AAS-mediated cardiovascular (CV) alterations were mostly taken from male subjects, even though women are also susceptible to the effects of AAS and gender-specific differences in susceptibility to vascular diseases exist. Here we investigate ND-induced vascular reactivity alterations in both sedentary and exercised female rats and whether these alterations depend on endothelium-derived factors. We show that chronic exposure of female Wistar rats to ND (20mg/Kg/week for 4weeks) impaired the vascular mesenteric bed (MVB) reactivity to vasodilator (acetylcholine) agonist. The endothelium-dependent Nitric Oxide (NO) component was reduced in ND-treated rats, whereas neither the endothelium-derived hyperpolarizing factor (EDHF) component nor prostanoids were altered in the MVBs. Endothelial dysfunction observed in ND-treated rats was associated with decreased eNOS (Ser¹¹⁷⁷) and Akt (Ser⁴⁷³) phosphorylation sites and upregulation of iNOS and NADPH oxidase expression. Exercise training by weight lifting in water did not improve the vascular alterations induced by ND treatment. ND treatment also significantly reduced the serum levels of estradiol in females, overriding its CV protective effect. These results help uncover the role of ND modulating endothelial function in the setting of CV disease caused by the abuse of AAS in females. If this translates to humans, young women abusing AAS can potentially lose the cardio protective effect rendered by estrogen and be more susceptible to CV alterations.

Evaluation of efforts in untrained Wistar rats following exercise on forced running wheel at maximal lactate steady state

[Purpose]

We aimed to examine the effect of running speed on metabolic responses associated with maximal lactate steady state (MLSS) in rats during forced running wheel (FRW) exercise.

[Methods]

Forty male adult Wistar rats were divided into seven groups. The blood lactate threshold and peak running speed were determined for an incremental power test group. Five groups participated in constant power tests at intensities 10, 13, 14.5, 16, and 17.5 m/min to determine MLSS and a non-exercise group was chosen as the control. Animals were euthanized immediately after constant power tests and their corticosterone, non-esterified fatty acid (NEFA), blood glucose, and creatine kinase (CK) levels analyzed. The differences among groups were identified by one-way analysis of variance (p < 0.05).

[Results]

Blood lactate threshold corresponded a running intensity of 15 m/min, while MLSS was determined to be 16 m/min. Serum corticosterone concentrations were significantly higher in 14.5, 16, and 17.5 m/min groups (298.8±62, 338.3±65, and 354±26 nM, respectively) as compared to that in the control group (210.6±16 nM). Concentrations of NEFA observed in groups 13, 14.5, 16, and 17.5 m/min (662.8±24, 702.35±69, 718.4±34, and 752.8±77 μM, respectively) were significantly higher than those in 10 m/min and control groups (511.1±53 and 412.1±56 μM, respectively). The serum CK concentration recorded for group 17.5 m/min (372.4±56 U/L) was higher than those recorded for other groups.

[Conclusion]

The speed above 16 m/min on FRW resulted in increased physiological demands and muscle damage in untrained healthy Wistar rats.

Leptin receptor knockout-induced depression-like behaviors and attenuated antidepressant effects of exercise are associated with STAT3/SOCS3 signaling

Relatively little has been known about pathophysiological mechanisms contributing to the development of neuropsychiatric symptoms in the context of metabolic syndrome. Impaired leptin signaling activation in db/db mice has been proposed as a potential link between behavioral and metabolic disorders. Our previous studies have shown that exercise has the beneficial effects on a depression-like and insulin-resistant state in mice. The present study aimed to determine whether and how leptin receptor knockout (db/db) induces depression-like behaviors, and to identify the antidepressant effects of swimming exercise in db/db mice. Our results support the validity of db/db mice as an animal model to study depression with metabolic abnormalities, but fail to confirm the improvement of exercise on depression. LepRb knockout-induced depression-like behaviors are associated with STAT3/SOCS3 signaling but independent of IKKβ/NFκB signaling. Our findings suggest the potential importance of LepRb as an exercise-regulated target for depression, also representing a new target underlying treatment-resistant depression.

Acute exercise boosts cell proliferation and the heat shock response in lymphocytes: correlation with cytokine production and extracellular-to-intracellular HSP70 ratio

Exercise stimulates immune responses, but the appropriate "doses" for such achievements are unsettled. Conversely, in metabolic tissues, exercise improves the heat shock (HS) response, a universal cytoprotective response to proteostasis challenges that are centred on the expression of the 70-kDa family of intracellular heat shock proteins (iHSP70), which are anti-inflammatory. Concurrently, exercise triggers the export of HSP70 towards the extracellular milieu (eHSP70), where they work as pro-inflammatory cytokines. As the HS response is severely compromised in chronic degenerative diseases of inflammatory nature, we wondered whether acute exercise bouts of different intensities could alter the HS response of lymphocytes from secondary lymphoid organs and whether this would be related to immunoinflammatory responses. Adult male Wistar rats swam for 20 min at low, moderate, high or strenuous intensities as per an overload in tail base. Controls remained at rest under the same conditions. Afterwards, mesenteric lymph node lymphocytes were assessed for the potency of the HS response (42 °C for 2 h), NF-κB binding activity, mitogen-stimulated proliferation and cytokine production. Exercise stimulated cell proliferation in an "inverted-U" fashion peaking at moderate load, which was paralleled by suppression of NF-κB activation and nuclear location, and followed by enhanced HS response in relation to non-exercised animals. Comparative levels of eHSP70 to iHSP70 (H-index) matched IL-2/IL-10 ratios. We conclude that exercise, in a workload-dependent way, stimulates immunoinflammatory performance of lymphocytes of tissues far from the circulation and this is associated with H-index of stress response, which is useful to assess training status and immunosurveillance balance.

Cerebellar Insulin/IGF-1 signaling in diabetic rats: Effects of exercise training

The Diabetes Mellitus (DM) is a chronic disease associated with loss of brain regions such as the cerebellum, increasing the risk of developing neurodegenerative diseases such as Parkinson's disease (PD). In the brain of diabetic and PD organisms the insulin/IGF-1 signaling is altered. Exercise training is an effective intervention for the prevention of neurodegerative diseases since it release neurotrophic factors and regulating insulin/IGF-1 signaling in the brain. This study aimed to evaluate the proteins involved in the insulin/IGF-1 pathway in the cerebellum of diabetic rats subjected to exercise training protocol. Wistar rats were distributed in four groups: sedentary control (SC), trained control (TC), sedentary diabetic (SD) and trained diabetic (TD). Diabetes was induced by Alloxan (ALX) (32mg/kgb.w.). The training program consisted in swimming 5days/week, 1h/day, during 6 weeks, supporting an overload corresponding to 90% of the anaerobic threshold. At the end, cerebellum was extracted to determinate the protein expression of GSK-3β, IRβ and IGF-1R and the phosphorylation of β-amyloid, Tau, ERK1+ERK2 by Western Blot analysis. All dependent variables were analyzed by one-way analysis of variance with significance level of 5%. Diabetes causes hyperglycemia in both diabetic groups; however, in TD, there was a reduction in hyperglycemia compared to SD. Diabetes increased Tau and β-amyloid phosphorylation in both SD and TD groups. Furthermore, aerobic exercise increased ERK1+ERK2 expression in TC. The data showed that in cerebellum of diabetic rats induced by alloxan there are some proteins expression like Parkinson cerebellum increased, and the exercise training was not able to modulate the expression of these proteins.

Lactate minimum underestimates the maximal lactate steady-state in swimming mice

The intensity of lactate minimum (LM) has presented a good estimate of the intensity of maximal lactate steady-state (MLSS); however, this relationship has not yet been verified in the mouse model. We proposed validating the LM protocol for swimming mice by investigating the relationship among intensities of LM and MLSS as well as differences between sexes, in terms of aerobic capacity. Nineteen mice (male: 10, female: 9) were submitted to the evaluation protocols for LM and MLSS. The LM protocol consisted of hyperlactatemia induction (30 s exercise (13% body mass (bm)), 30 s resting pause and exhaustive exercise (13% bm), 9 min resting pause and incremental test). The LM underestimated MLSS (mice: 17.6%; male: 13.5%; female: 21.6%). Pearson's analysis showed a strong correlation among intensities of MLSS and LM (male (r = 0.67, p = 0.033); female (r = 0.86, p = 0.003)), but without agreement between protocols. The Bland-Altman analysis showed that bias was higher for females (1.5 (0.98) % bm; mean (MLSS and LM): 4.4%-6.4% bm) as compared with males (0.84 (1.24) % bm; mean (MLSS and LM): 4.5%-7.5% bm). The error associated with the estimated of intensity for males was lower when compared with the range of means for MLSS and LM. Therefore, the LM test could be used to determine individual aerobic intensity for males (considering the bias) but not females. Furthermore, the females supported higher intensities than the males. The differences in body mass between sexes could not explain the higher intensities supported by the females.

Strength Training Prevents Hyperinsulinemia, Insulin Resistance, and Inflammation Independent of Weight Loss in Fructose-Fed Animals

The aim of this study was to compare the effects of aerobic, strength, and combined training on metabolic disorders induced by a fructose-rich diet. Wistar rats (120 days old) were randomized into five groups (n = 8-14): C (control diet and sedentary), F (fed the fructose-rich diet and sedentary), FA (fed the fructose-rich diet and subject to aerobic exercise), FS (fed the fructose-rich diet and subject to strength exercise), and FAS (fed the fructose-rich diet and subject to combined aerobic and strength exercises). After the 8-week experiment, glucose homeostasis, blood biochemistry, tissue triglycerides, and inflammation were evaluated and analyzed. The strength protocol exerted greater effects on glucose homeostasis, insulin sensitivity, and liver lipid contents than other protocols (all P < 0.05). All three exercise protocols induced a remarkable reduction in inflammation, tissue triglyceride content, and inflammatory pathways, which was achieved through c-Jun NH2-terminal kinase (JNK) phosphorylation and factor nuclear kappa B (NFkB) activation in both the liver and the muscle. Our data suggest that strength training reduced the severity of most of the metabolic disorders induced by a fructose-rich diet and could be the most effective strategy to prevent or treat fructose-induced metabolic diseases.

Oxidative status of the myocardium in response to different intensities of physical training

The intensity of exercise determines the metabolic pathway and the energetic substrate that is spent. Our study sought to identify the effects of different intensities of swimming on myocardial oxidative status and the blood lipid profile. Eighty Wistar rats (male and female) submitted to different intensities of a swimming regimen (low, LS; moderate, MS; or high, HS) for 16 weeks. Samples of blood and myocardium from the left ventricle were collected to determine lipid profiles and oxidative status. Reactive oxygen species (ROS) and antioxidant capacity against peroxyl radicals (ACAP), lipid profiles and lipid peroxidation was analyzed. ROS levels and ACAP were higher in male rats than in female rats overall (p<0.05). However, ACAP in the myocardium was significantly elevated in LS female rats compared to the MS and HS female rats, which had a significantly lower ACAP compared to all other groups. LS and MS training in both sexes and HS training (in females) led to significant decreases in the heart's lipid peroxidation. Amelioration of the lipid profile and reduction in oxidative damage contributed to a physiological state that benefits cardiovascular function in exercised animals. The results show that low and moderate intensity exercise promotes beneficial adaptations.

Severe Obesity Shifts Metabolic Thresholds but Does Not Attenuate Aerobic Training Adaptations in Zucker Rats

Severe obesity affects metabolism with potential to influence the lactate and glycemic response to different exercise intensities in untrained and trained rats. Here we evaluated metabolic thresholds and maximal aerobic capacity in rats with severe obesity and lean counterparts at pre- and post-training. Zucker rats (obese: n = 10, lean: n = 10) were submitted to constant treadmill bouts, to determine the maximal lactate steady state, and an incremental treadmill test, to determine the lactate threshold, glycemic threshold and maximal velocity at pre and post 8 weeks of treadmill training. Velocities of the lactate threshold and glycemic threshold agreed with the maximal lactate steady state velocity on most comparisons. The maximal lactate steady state velocity occurred at higher percentage of the maximal velocity in Zucker rats at pre-training than the percentage commonly reported and used for training prescription for other rat strains (i.e., 60%) (obese = 78 ± 9% and lean = 68 ± 5%, P < 0.05 vs. 60%). The maximal lactate steady state velocity and maximal velocity were lower in the obese group at pre-training (P < 0.05 vs. lean), increased in both groups at post-training (P < 0.05 vs. pre), but were still lower in the obese group at post-training (P < 0.05 vs. lean). Training-induced increase in maximal lactate steady state, lactate threshold and glycemic threshold velocities was similar between groups (P > 0.05), whereas increase in maximal velocity was greater in the obese group (P < 0.05 vs. lean). In conclusion, lactate threshold, glycemic threshold and maximal lactate steady state occurred at similar exercise intensity in Zucker rats at pre- and post-training. Severe obesity shifted metabolic thresholds to higher exercise intensity at pre-training, but did not attenuate submaximal and maximal aerobic training adaptations.

EFEITOS DO EXERCÍCIO FÍSICO EM COMPORTAMENTOS RELACIONADOS COM A ANSIEDADE EM RATOS

Introdução: Os efeitos do exercício físico são associados à redução da ansiedade e à manutenção desse estado por diversas horas. Contudo, poucos trabalhos têm investigado os efeitos do exercício agudo sobre a ansiedade. Objetivo: Investigar o efeito agudo da intensidade do exercício físico sobre comportamento relacionado com a ansiedade em modelos animais. Métodos: Cinquenta e seis ratos Wistar machos foram distribuídos aleatoriamente em oito grupos: controle, 0%, 5% e 50% de carga correspondente ao peso corporal dos animais. Os grupos foram submetidos a um protocolo de natação que consistiu na realização de 30 minutos de exercício para os grupos 0% e 5% e dez sessões de dez saltos intercalados por um minuto de descanso para o grupo 50%. Após a natação, os animais foram expostos aos testes de campo aberto e labirinto em cruz elevado. Os dados foram avaliados estatisticamente pela One-way ANOVA e teste post hoc de Bonferroni, adotando-se P<0,05. Resultados: Na análise dos dados no teste de campo aberto foram encontradas diferenças significativas nas medidas de cruzamento (F(3,20) = 9,60; p < 0,01), ocorrendo um aumento de cruzamentos do grupo 5% (81,2 ± 14,8) com relação ao grupo controle (45,0 ± 8,7). Foi encontrada diferença significativa no percentual de entrada nos braços abertos (F(3,28) = 5,63; p < 0,01), havendo uma diminuição no grupo 50% (25,4 ± 17,0) com relação ao grupo controle (46,8 ± 9,1). Conclusão: A prática de exercício físico na intensidade de 5% apresentou efeitos ansiolíticos, enquanto na intensidade de 50%, apresentou efeitos ansiogênicos.

Acute Aerobic Swimming Exercise Induces Distinct Effects in the Contractile Reactivity of Rat Ileum to KCl and Carbachol

Aerobic exercise promotes short-term physiological changes in the intestinal smooth muscle associated to the ischemia-reperfusion process; however, few studies have demonstrated its effect on the intestinal contractile function. Thus, this work describes our observations regarding the influence of acute aerobic swimming exercise in the contractile reactivity, oxidative stress, and morphology of rat ileum. Wistar rats were divided into sedentary (SED) and acutely exercised (EX-AC) groups. Animals were acclimated by 10, 10, and 30 min of swimming exercise in intercalated days 1 week before exercise. Then they were submitted to forced swimming for 1 h with a metal of 3% of their body weight attached to their body. Animals were euthanized immediately after the exercise section and the ileum was suspended in organ baths for monitoring isotonic contractions. The analysis of lipid peroxidation was performed in order to determinate the malondialdehyde (MDA) levels as a marker of oxidative stress, and intestinal smooth muscle morphology by histological staining. Cumulative concentration-response curves to KCl were altered in the EX-AC with an increase in both its efficacy and potency (E_max = 153.2 ± 2.8%, EC₅₀ = 1.3 ± 0.1 × 10⁻² M) compared to the SED group (E_max = 100%, EC₅₀ = 1.8 ± 0.1 × 10⁻² M). Interestingly, carbachol had its efficacy and potency reduced in the EX-AC (E_max = 67.1 ± 1.4%, EC₅₀ = 9.8 ± 1.4 × 10⁻⁷ M) compared to the SED group (E_max = 100%, EC₅₀ = 2.0 ± 0.2 × 10⁻⁷ M). The exercise did not alter the MDA levels in the ileum (5.4 ± 0.6 μ mol/mL) in the EX-AC compared to the SED group (8.4 ± 1.7 μ mol/mL). Moreover, neither the circular nor the longitudinal smooth muscle layers thickness were modified by the exercise (66.2 ± 6.0 and 40.2 ± 2.6 μm, respectively), compared to the SED group (61.6 ± 6.4 and 34.8 ± 3.7 μm, respectively). Therefore, the ileum sensitivity to contractile agents is differentially altered by the acute aerobic swimming exercise, without affecting the oxidative stress and the morphology of ileum smooth muscle.

Cardiopulmonary reflex, cardiac cytokines, and nandrolone decanoate: response to resistance training in rats

This study evaluated the effects of nandrolone associated with resistance training (RT) on cardiac cytokines, angiotensin-converting enzyme activity (ACEA), and the sensitivity of the Bezold-Jarisch reflex (BJR). Male Wistar rats were divided into 3 groups: CONT (received vehicle, no training); EXERC (RT: after one week of water adaptation, rats were exercised by jumping into water twice a week for 4 weeks), and ND+EXERC (received nandrolone decanoate 10 mg/kg, twice/week, i.m, associated with RT). The BJR was analysed by measuring bradycardic and hypotensive responses elicited by serotonin administration. Myocyte hypertrophy and matrix collagen deposition were determined by morphometric analysis of H&E and picrosirius red-stained samples, respectively. TNF-α and ACEA were also studied. RT promoted physiological myocyte hyrpertrophy but did not cause changes in the other parameters. The association of ND with RT increased myocyte hypertrophy, deposition of matrix type I collagen, TNF-α and ACEA; decreased IL-10, and impairment in the BJR were observed in ND+EXERC compared with CONT and EXERC. ND is associated with alterations in cardiac structure and function as a result of the development of pathological cardiac hypertrophy (cardiac cytokine imbalance, elevation of ACEA) and cardiac injury, even when combined with resistance training.

Chronic aerobic swimming exercise promotes functional and morphological changes in rat ileum

In the present study, we evaluated the influence of chronic swimming aerobic exercise on the contractile reactivity, lipid peroxidation and tissue morphology of small intestine from rats. We showed that, accordingly to the time of exercise, the rat ileum has its contractile reactivity reduced, in addition to the increased lipid peroxidation followed by its reestablishment to basal levels, as well as the augmented longitudinal smooth muscle layer thickness together with the reduced circular thickness.

Several studies have reported the gastrointestinal (GI) effects promoted by the physical exercise. Thus, we aimed to evaluate the influence of swimming exercise on the contractile reactivity, lipid peroxidation and morphology of rat ileum. Wistar rats were divided into sedentary (SED) and groups exercised for two (EX2), four (EX4), six (EX6) or eight (EX8) weeks, 5 days/week. Animals were killed; the ileum was removed and suspended in organ baths where the isotonic contractions were recorded. Lipid peroxidation was evaluated by MDA (malondialdehyde) measurement with TBARS (thiobarbituric acid reactive substances) assay and morphology by histological staining. Cumulative concentration-response curves to KCl were attenuated, as the E_max values were changed from 100% (SED) to 63.1±3.9 (EX2), 48.8±3.8 (EX4), 19.4±1.8 (EX6) and 59.4±2.8% (EX8). Similarly, cumulative concentration-response curves to carbamylcholine hydrochloride (CCh) were attenuated, as the E_max values were changed from 100% (SED) to 74.1±5.4 (EX2), 75.9±5.2 (EX4) and 62.9±4.6 (EX6), but not in the EX8 (89.7±3.4%). However, CCh potency was increased in this latter, as the EC₅₀ was altered from 1.0±0.1×10⁻⁶ (SED) to 2.1±0.4×10⁻⁷ (EX8). MDA concentration was altered only in EX4 (44.3±4.4) compared with SED (20.6±3.6 μmol/l). Circular layer was reduced in SED when compared with the exercised groups. Conversely, longitudinal layer was increased. In conclusion, chronic swimming exercise reduces the ileum contraction, equilibrates the oxidative damage and promotes changes in tissue size to establish an adaptation to the exercise.

Blood lactate minimum of rats during swimming test using three incremental stages

AbstractThe purpose of this study was to determine the lactate minimum intensity (LMI) by swimming LACmintest using three incremental stages (LACmintest3) and to evaluate its sensitivity to changes in aerobic fitness (AF). Twenty Wistar rats performed: LACmintest3 (1): induction of hyperlactacidemia and incremental phase (4%, 5% and 6.5% of bw); Constant loads tests on (2) and above (3) the LMI. Half of the animals were subjected to training with the individual LMI and the tests were performed again. The mean exercise load in LACmintest3 was 5.04 ± 0.13% bw at 5.08 ± 0.55 mmol L-1 blood lactate minimum (BLM). There was a stabilize and disproportionate increase of blood lactate in tests 2 and 3, respectively. After the training period, the mean BLM was lower in the trained animals. The LACmintest3 seems to be a good indicator of LMI and responsive to changes in AF in rats subjected to swim training.

Impact of high intensity exercise on muscle morphology in EAE rats

The impact of high-intensity exercise on disease progression and muscle contractile properties in experimental autoimmune encephalomyelitis (EAE) remains unclear. Control (CON) and EAE rats were divided into sedentary and exercise groups. Before onset (experiment 1, n=40) and after hindquarter paralysis (experiment 2, n=40), isokinetic foot extensor strength, cross sectional area (CSA) of tibialis anterior (TA), extensor digitorum longus (EDL) and soleus (SOL) and brain-derived neurotrophic factor (BDNF) levels were assessed. EAE reduced muscle fiber CSA of TA, EDL and SOL. In general, exercise was not able to affect CSA, whereas it delayed hindquarter paralysis peak. CON muscle work peaked and declined, while it remained stable in EAE. BDNF-responses were not affected by EAE or exercise. In conclusion, EAE affected CSA-properties of TA, EDL and SOL, which could, partly, explain the absence of peak work during isokinetic muscle performance in EAE-animals. However, exercise was not able to prevent muscle fiber atrophy.

Critical velocity estimates lactate minimum velocity in youth runners

In order to investigate the validity of critical velocity (CV) as a noninvasive method to estimate the lactate minimum velocity (LMV), 25 youth runners underwent the following tests: 1) 3,000m running; 2) 1,600m running; 3) LMV test. The intensity of lactate minimum was defined as the velocity corresponding to the lowest blood lactate concentration during the LMV test. The CV was determined using the linear model, defined by the inclination of the regression line between distance and duration in the running tests of 1,600 and 3,000m. There was no significant difference (p=0.3055) between LMV and CV. In addition, both protocols presented a good agreement based on the small difference between means and the narrow levels of agreement, as well as a standard error of estimation classified as ideal. In conclusion, CV, as identified in this study, may be an alternative for noninvasive identification of LMV.

Physical training at sub-threshold intensity reduces the prevalence of hepatic steatosis after high-fat diet in rats

The purpose of the present study was to evaluate the effects of swimming physical training with sub-threshold load on the prevalence of hepatic steatosis in Wistar rats fed high-fat diets (cafeteria or baru). After 2 months of cafeteria diet administration, the rats were separated into 6 groups: Sedentary or Trained Baru diet; Sedentary or Trained Cafeteria diet; Sedentary or Trained standard diet. The trained groups were subjected to swimming exercise at sub-threshold intensity (2% of body weight) during 8 weeks, 5x/week, 1h/day. The body weight and hepatohistological changes were analyzed. Sedentary groups fed high-fat diets presented higher body weight gain when compared to control trained group. The swimming training at the proposed intensity was able to prevent the hepatic steatosis in rats fed high-fat diets.

Increased lactate threshold after five weeks of treadmill aerobic training in rats

The aim of the present study was to analyse the lactate threshold (LT) changes in rats submitted to an aerobic treadmill-training programme. Twenty-five Wistar rats were divided into two groups: a sedentary control group (CG), and a trained group (TG) submitted to an aerobic training during 5 weeks. All the animals were submitted to an incremental treadmill exercise test in order to determine LT. There was an increase in the maximum running speed in the TG (from 32.25 ± 1.27 to 47.75 ± 3.13 m.min-1 - p = 0.001), and running speed at LT (from 26.21 ± 1.15 to 35.30 ± 2.24 m.min-1 - p = 0.004), a part from the reduction in blood lactate at LT. LT can be determined in rats, and aerobic training induced positive oxidative physiological adaptations in the animals.

Caffeine suppresses exercise-enhanced long-term and location memory in middle-aged rats: Involvement of hippocampal Akt and CREB signaling

The cognitive function decline is closely related with brain changes generated by age. The ability of caffeine and exercise to prevent memory impairment has been reported in animal models and humans. The purpose of the present study was to investigate whether swimming exercise and caffeine administration enhance memory in middle-aged Wistar rats. Male Wistar rats (18months) received caffeine at a dose of 30mg/kg, 5days per week by a period of 4weeks. Animals were subjected to swimming training with a workload (3% of body weight, 20min per day for 4weeks). After 4weeks, the object recognition test (ORT) and the object location test (OLT) were performed. The results of this study demonstrated that caffeine suppressed exercise-enhanced long-term (ORT) and spatial (OLT) memory in middle-aged and this effect may be related to a decrease in hippocampal p-CREB signaling. This study also provided evidence that the effects of this protocol on memory were not accompanied by alterations in the levels of activated Akt. The [(3)H] glutamate uptake was reduced in hippocampus of rats administered with caffeine and submitted to swimming protocol.

Effect of physical training on liver expression of activin A and follistatin in a nonalcoholic fatty liver disease model in rats

Nonalcoholic fatty liver disease (NAFLD) is characterized by fat accumulation in the liver and is associated with obesity and insulin resistance. Activin A is a member of the transforming growth factor beta (TGF)-β superfamily and inhibits hepatocyte growth. Follistatin antagonizes the biological actions of activin. Exercise is an important therapeutic strategy to reduce the metabolic effects of obesity. We evaluated the pattern of activin A and follistatin liver expression in obese rats subjected to swimming exercise. Control rats (C) and high-fat (HF) diet-fed rats were randomly assigned to a swimming training group (C-Swim and HF-Swim) or a sedentary group (C-Sed and HF-Sed). Activin βA subunit mRNA expression was significantly higher in HF-Swim than in HF-Sed rats. Follistatin mRNA expression was significantly lower in C-Swim and HF-Swim than in either C-Sed or HF-Sed animals. There was no evidence of steatosis or inflammation in C rats. In contrast, in HF animals the severity of steatosis ranged from grade 1 to grade 3. The extent of liver parenchyma damage was less in HF-Swim animals, with the severity of steatosis ranging from grade 0 to grade 1. These data showed that exercise may reduce the deleterious effects of a high-fat diet on the liver, suggesting that the local expression of activin-follistatin may be involved.

Treatment with nebivolol combined with physical training promotes improvements in the cardiovascular responses of hypertensive rats

The aim of this study was to determine whether exercise training combined with beta-blocker treatment promotes additional cardiovascular benefits compared with either intervention on its own. For this we used 76 Wistar rats distributed among different groups: normotensive sedentary (NS), normotensive trained (NT), normotensive sedentary treated with beta-blocker (NS_BB), normotensive trained treated with beta-blocker (NT_BB), hypertensive sedentary (HS), hypertensive trained (HT), hypertensive sedentary treated with a beta-blocker (HS_BB), and hypertensive trained rats treated with beta-blocker (HT_BB). Exercise training consisted of 4 weeks of swimming for 60 min a day, 5 days a week. Hypertension was induced with l-NAME (4 weeks), whereas the control rats received saline, and both the control and test rats received nebivolol. The animals underwent surgery to directly record their blood pressure. The HS group showed higher mean arterial pressure (MAP) (P = 0.000), systolic arterial pressure (P = 0.000), and diastolic arterial pressure (P = 0.000) compared with NS. MAP was higher in the HS compared with the HT (P = 0.002), HS_BB (P = 0.018), and HT_BB (P = 0.015) groups. Hearts from the HS group had a higher percentage of collagen compared with the NS and HS_BB groups. The HT_BB and HT groups only had a higher percentage of cardiac collagen by comparison with the HS_BB group. The HT_BB group showed higher levels of macrophages and neutrophils by comparison with the HT and HS_BB groups. Thus, treatment with a beta-blocker combined with physical training was associated with increased cardiovascular benefits over either intervention alone.

Sodium bicarbonate treatment prevents gastric emptying delay caused by acute exercise in awake rats

Physical exercise, mainly after vigorous activity, may induce gastrointestinal dysmotility whose mechanisms are still unknown. We hypothesized that physical exercise and ensuing lactate-related acidemia alter gastrointestinal motor behavior. In the present study, we evaluated the effects of short-term exercise on gastric emptying rate in awake rats subjected to 15-min swimming sessions against a load equivalent to 5% of their body weight. After 0, 10, or 20 min of exercise testing, the rats were gavage fed with 1.5 ml of a liquid test meal (0.5 mg/ml of phenol red in 5% glucose solution) and euthanized 10 min postprandially to measure fractional gastric dye recovery. In addition to inducing acidemia and increasing blood lactate levels, acute exercise increased (P < 0.05) gastric retention. Such a phenomenon presented a positive correlation (P < 0.001) between blood lactate levels and fractional gastric dye recovery. Gastric retention and other acidbase-related changes were all prevented by NaHCO3 pretreatment. Additionally, exercise enhanced (P < 0.05) the marker's progression through the small intestine. In anesthetized rats, exercise increased (P < 0.05) gastric volume, measured by a balloon catheter in a barostat system. Compared with sedentary control rats, acute exercise also inhibited (P < 0.05) the contractility of gastric fundus strips in vitro. In conclusion, acute exercise delayed the gastric emptying of a liquid test meal by interfering with the acid-base balance.