Exercise training intensity/volume affects plasma and tissue adiponectin concentrations in the male rat

Moderate-Intensity Constant and High-Intensity Interval Training Confer Differential Metabolic Benefits in Skeletal Muscle, White Adipose Tissue, and Liver of Candidates to Undergo Bariatric Surgery

Background/Objectives: Bariatric surgery candidates require presurgical physical training, therefore, we compared the metabolic effects of a constant moderate-intensity training program (MICT) vs. a high-intensity interval training (HIIT) in this population. Methods: Seventeen participants performed MICT (n = 9, intensity of 50% of heart rate reserve (HRR) and/or 4-5/10 subjective sensation of effort (SSE)) or HIIT (n = 8, 6 cycles of 2.5 min at 80% of the HRR and/or 7-8/10 of SSE, interspersed by 6 cycles of active rest at 20% of the FCR) for 10 sessions for 4 weeks. After training, tissue samples (skeletal muscle, adipose tissue, and liver) were extracted, and protein levels of adiponectin, GLUT4, PGC1α, phospho-AMPK/AMPK, collagen 1 and TGFβ1 were measured. Results: Participants who performed MICT showed higher protein levels of PGC-1α in skeletal muscle samples (1.1 ± 0.27 vs. 0.7 ± 0.4-fold change, p < 0.05). In the liver samples of the people who performed HIIT, lower protein levels of phospho-AMPK/AMPK (1.0 ± 0.37 vs. 0.52 ± 0.22-fold change), PGC-1α (1.0 ± 0.18 vs. 0.69 ± 0.15-fold change), and collagen 1 (1.0 ± 0.26 vs. 0.59 ± 0.28-fold change) were observed (all p < 0.05). In subcutaneous adipose tissue, higher adiponectin levels were found only after HIIT training (1.1 ± 0.48 vs. 1.9 ± 0.69-fold change, p < 0.05). Conclusions: Our results show that both MICT and HIIT confer metabolic benefits in candidates undergoing bariatric surgery; however, most of these benefits have a program-specific fashion. Future studies should aim to elucidate the mechanisms behind these differences.

Adipose-Muscle crosstalk in age-related metabolic disorders: The emerging roles of adipo-myokines

Obesity and type 2 diabetes account for a considerable proportion of the global burden of age-related metabolic diseases. In age-related metabolic diseases, tissue crosstalk and metabolic regulation have been primarily linked to endocrine processes. Skeletal muscle and adipose tissue are endocrine organs that release myokines and adipokines into the bloodstream, respectively. These cytokines regulate metabolic responses in a variety of tissues, including skeletal muscle and adipose tissue. However, the intricate mechanisms underlying adipose-muscle crosstalk in age-related metabolic diseases are not fully understood. Recent exciting evidence suggests that myokines act to control adipose tissue functions, including lipolysis, browning, and inflammation, whereas adipokines mediate the beneficial actions of adipose tissue in the muscle, such as glucose uptake and metabolism. In this review, we assess the mechanisms of adipose-muscle crosstalk in age-related disorders and propose that the adipokines adiponectin and spexin, as well as the myokines irisin and interleukin-6 (IL-6), are crucial for maintaining the body's metabolic balance in age-related metabolic disorders. In addition, these changes of adipose-muscle crosstalk in response to exercise or dietary flavonoid consumption are part of the mechanisms of both functions in the remission of age-related metabolic disorders. A better understanding of the intricate relationships between adipose tissue and skeletal muscle could lead to more potent therapeutic approaches to prolong life and prevent age-related metabolic diseases.

Molecular mechanisms of exercise contributing to tissue regeneration

Physical activity has been known as an essential element to promote human health for centuries. Thus, exercise intervention is encouraged to battle against sedentary lifestyle. Recent rapid advances in molecular biotechnology have demonstrated that both endurance and resistance exercise training, two traditional types of exercise, trigger a series of physiological responses, unraveling the mechanisms of exercise regulating on the human body. Therefore, exercise has been expected as a candidate approach of alleviating a wide range of diseases, such as metabolic diseases, neurodegenerative disorders, tumors, and cardiovascular diseases. In particular, the capacity of exercise to promote tissue regeneration has attracted the attention of many researchers in recent decades. Since most adult human organs have a weak regenerative capacity, it is currently a key challenge in regenerative medicine to improve the efficiency of tissue regeneration. As research progresses, exercise-induced tissue regeneration seems to provide a novel approach for fighting against injury or senescence, establishing strong theoretical basis for more and more "exercise mimetics." These drugs are acting as the pharmaceutical alternatives of those individuals who cannot experience the benefits of exercise. Here, we comprehensively provide a description of the benefits of exercise on tissue regeneration in diverse organs, mainly focusing on musculoskeletal system, cardiovascular system, and nervous system. We also discuss the underlying molecular mechanisms associated with the regenerative effects of exercise and emerging therapeutic exercise mimetics for regeneration, as well as the associated opportunities and challenges. We aim to describe an integrated perspective on the current advances of distinct physiological mechanisms associated with exercise-induced tissue regeneration on various organs and facilitate the development of drugs that mimics the benefits of exercise.

Adiponectin overexpression in C2C12 myocytes increases lipid oxidation and myofiber transition

Metabolic syndrome and obesity have detrimental effects on the metabolic function of the skeletal muscle. Mounting evidence indicates that patients with those conditions may present an increased ratio of glycolytic to oxidative fibers associated with a decrease in oxidative capacity. In this regard, adiponectin, a hormone mainly secreted by adipocytes that regulates glucose and lipid metabolism, has emerged as a myokine that could play an important role in this process. We aimed to investigate whether adiponectin overexpression in skeletal muscle might be a local protective mechanism, favoring fatty acid utilization. To that end, we generated an in vitro model of myocytes with upregulated endogenous adiponectin using a lentiviral carrier. We demonstrated that the adiponectin-transduced myocytes were able to produce and secrete fully functional adiponectin complexes. Adiponectin overexpression remarkably upregulated the mRNA level of myogenic regulatory factors as well as genes implicated in lipolysis (HSL, ATGL) and cellular and mitochondrial fatty acid transport (LPL, CD36, CPT1B). This was accompanied by increased isoproterenol-induced lipolysis and β-oxidation and reduced lipogenesis, whereas insulin-stimulated glucose uptake was unaltered in transduced myocytes. Lastly, the relative expression of the more glycolytic myofibers (MyHC IIb) compared to the more oxidative ones (MyHC I) was notably reduced. Our results showed that the released adiponectin acted in an autocrine/paracrine manner, increasing lipid oxidation in myocytes and leading to a transition of myofibers from the glycolytic to the oxidative type. In conclusion, muscle adiponectin overexpression might be a way to relieve muscle diseases caused by oxidative muscle fiber deficiency.

Effect of exercise training on gene expression of adiponectin and its receptors in testicles and sex hormones in diabetic rats

Adiponectin and its receptors are expressed in the male reproductive system, which play a role in regulating male sex hormones and fertility. Diabetes was induced by Streptozotocin-Nicotinamide (STZ-NA i.p) in rats and after performing the trainings, adiponectin gene expression and its receptors in the testis were evaluated using real time PCR, and blood serum was then used in order to assess FSH, LH and testosterone. The STZ-NA significantly increased the fasting blood glucose, gene expression of adiponectin AdipoR1 in the testicles of diabetic rats. A significant reduction in serum testosterone and LH levels were observed in the diabetic group. Resistance and endurance training decreased blood glucose, adiponectin and AdipoR1 gene, and also increased the serum testosterone and LH levels in diabetic rats. Overall, our data suggest the role played by training in improve expression of adiponectin and AdipoR1 gene by increasing the serum testosterone and LH levels in type 2 diabetic rats.

Effect of uphill walking on browning factor and high molecular weight-adiponectin in postmenopausal women

Metabolic disorders occurring in menopause, including dyslipidemia, disorders of carbohydrate metabolism, components of metabolic syndrome, constitute risk factors for cardiovascular disease in women. Irisin and fibroblast growth factor-21 (FGF-21), which regulate browning, and high molecular weight (HMW) adiponectin have emerged beneficial for metabolic health. The purpose of the study was to examine the effect of endurance aerobic exercise on circulating browning factor and HMW-adiponectin level in postmenopausal women. Twenty-five postmenopausal women were included in this study. The aerobic exercise program consisted of 60 min of walking exercise at 50%–60% maximum oxygen uptake, and conducted 3 times per week for 6 weeks. Body composition, blood pressure, lipid profiles, physical fitness, and concentration of plasma irisin, FGF-21, HMW-adiponectin were analyzed before and after exercise. Waist circumference, systolic blood pressure, and triglyceride levels decreased, and levels of high-density lipoprotein cholesterol, irisin increased after exercise. However, there were no significant changes in FGF-21 and HMW-adiponectin. Balance and flexibility among physical fitness indices improved after exercise. These results suggested that moderate intensity walking could be the ideal type of exercise in menopausal women to induce a positive change in metabolic health markers, including an increase in irisin levels. Further studies are needed to determine the effects of exercise on brown adipose tissue browning factor.

Exercise Alleviates Obesity-Induced Metabolic Dysfunction via Enhancing FGF21 Sensitivity in Adipose Tissues

Exercise promotes adipose remodeling and improves obesity-induced metabolic disorders through mechanisms that remain obscure. Here, we identify the FGF21 signaling in adipose tissues as an obligatory molecular transducer of exercise conferring its metabolic benefits in mice. Long-term high fat diet-fed obese mice exhibit compromised effects of exogenous FGF21 on alleviation of hyperglycemia, hyperinsulinemia, and hyperlipidemia, accompanied with markedly reduced expression of FGF receptor-1 (FGFR1) and β-Klotho (KLB) in adipose tissues. These impairments in obese mice are reversed by treadmill exercise. Mice lacking adipose KLB are refractory to exercise-induced alleviation of insulin resistance, glucose dysregulation, and ectopic lipid accumulation due to diminished adiponectin production, excessive fatty acid release, and enhanced adipose inflammation. Mechanistically, exercise induces the adipose expression of FGFR1 and KLB via peroxisome proliferator-activated receptor-gamma-mediated transcriptional activation. Thus, exercise sensitizes FGF21 actions in adipose tissues, which in turn sends humoral signals to coordinate multi-organ crosstalk for maintaining metabolic homeostasis.

Adiponectin and Its Mimics on Skeletal Muscle: Insulin Sensitizers, Fat Burners, Exercise Mimickers, Muscling Pills … or Everything Together?

Adiponectin (ApN) is a hormone abundantly secreted by adipocytes and it is known to be tightly linked to the metabolic syndrome. It promotes insulin-sensitizing, fat-burning, and anti-atherosclerotic actions, thereby effectively counteracting several metabolic disorders, including type 2 diabetes, obesity, and cardiovascular diseases. ApN is also known today to possess powerful anti-inflammatory/oxidative and pro-myogenic effects on skeletal muscles exposed to acute or chronic inflammation and injury, mainly through AdipoR1 (ApN specific muscle receptor) and AMP-activated protein kinase (AMPK) pathway, but also via T-cadherin. In this review, we will report all the beneficial and protective properties that ApN can exert, specifically on the skeletal muscle as a target tissue. We will highlight its effects and mechanisms of action, first in healthy skeletal muscle including exercised muscle, and second in diseased muscle from a variety of pathological conditions. In the end, we will go over some of AdipoRs agonists that can be easily produced and administered, and which can greatly mimic ApN. These interesting and newly identified molecules could pave the way towards future therapeutic approaches to potentially prevent or combat not only skeletal muscle disorders but also a plethora of other diseases with sterile inflammation or metabolic dysfunction.

Skeletal muscle adiponectin induction in obesity and exercise

Recent scientific efforts have focused on the detrimental effects that obesity has on the metabolic function of skeletal muscles and whether exercise can improve this dysfunction. In this regard, adiponectin, with important metabolic functions (e.g. insulin-sensitizer and anti-inflammatory), has been recently described as a myokine that acts in an autocrine/paracrine manner. Earlier studies reported that muscle adiponectin could be induced by pro-inflammatory mediators (e.g. lipopolysaccharide), cytokines, and high-fat diets, providing a protective mechanism of this tissue against metabolic insults. However, when metabolic insults such as high-fat diets are sustained this protective response becomes dysregulated, making the skeletal muscle susceptible to metabolic impairments. Recent studies have suggested that exercise could prevent or even reverse this process. Considering that most scientific knowledge on adiponectin dysregulation in obesity is from the study of adipose tissue, the present review summarizes and discusses the literature available to date regarding the effects of obesity on skeletal muscle adiponectin induction, along with the potential effects of different exercise prescriptions on this response in an obesity context.

Potential exerkines for physical exercise-elicited pro-cognitive effects: Insight from clinical and animal research

A sedentary lifestyle is now known as a critical risk factor for accelerated aging-related neurodegenerative disorders. In contract, having regular physical exercise has opposite effects. Clinical findings have suggested that physical exercise can promote brain plasticity, particularly the hippocampus and the prefrontal cortex, that are important for learning and memory and mood regulations. However, the underlying mechanisms are still unclear. Animal studies reveal that the effects of physical exercise on promoting neuroplasticity could be mediated by different exerkines derived from the peripheral system and the brain itself. This book chapter summarizes the recent evidence from clinical and pre-clinical studies showing the emerging mediators for exercise-promoted brain health, including myokines secreted from skeletal muscles, adipokines from adipose tissues, and other factors secreted from the bone and liver.

Effects of Moderate- and High-Intensity Chronic Exercise on the Adiponectin Levels in Slow-Twitch and Fast-Twitch Muscles in Rats

Background and objectives: Adipose tissue and skeletal muscle secrete adiponectin, a hormone abundantly secreted by adipocytes, that through the adiponectin receptor, regulate glucose and lipid metabolism. Adiponectin appears to protect skeletal muscles from inflammatory damage induced by oxidative stress. It has been suggested that decreased adiponectin levels could be associated with pathologic conditions, including obesity and diabetes. Furthermore, some studies suggest that exercise could have a beneficial effect by increasing adiponectin levels, but this observation remains controversial. It is also unknown if physical exercise modifies adiponectin expression in skeletal muscles. The aim of this study was to investigate the effect of chronic exercise on serum adiponectin and adiponectin expression in slow-twitch (soleus) and fast-twitch (plantaris) muscles in healthy rats. Materials and methods: Two-month-old male Wistar rats were randomly divided into three groups with n = 6 in each group: control (C), moderate-intensity training (MIT), and high-intensity training (HIT). The rats were conditioned to run on a treadmill for the 8-week period. Forty-eight hours after the last session, blood samples were collected for adiponectin measurements and total RNA was isolated from plantaris and soleus muscles to measure by RT-qPCR adiponectin receptor 1 and adiponectin mRNA expression level. Results: MIT and HIT groups had reduced adiponectin protein levels in serum and the plantaris muscle, but not changes in adiponectin protein were observed in the soleus muscle. No significant differences in Adiponectin receptor 1 (AdipoR1) gene expression were observed following intense or moderate exercise in either muscle group studied. Conclusions: Our study shows that decreasing levels of circulating adiponectin is a result of physical exercise and should not be generalized as a predictive marker of disease.

Impact of Exercise on Inflammatory Mediators of Metabolic and Vascular Insulin Resistance in Type 2 Diabetes

The development of obesity is cornerstone in the etiology of metabolic and vascular insulin resistance and consequently exacerbates glycemic control. Exercise is an efficacious first-line therapy for type 2 diabetes that improves insulin action through, in part, reducing hormone mediated inflammation. Together, improving the coordination of skeletal muscle metabolism with vascular delivery of glucose will be required for optimizing type 2 diabetes and cardiovascular disease treatment.

Mitochondrial dynamics as an underlying mechanism involved in aerobic exercise training-induced cardioprotection against ischemia-reperfusion injury

AIMS

Ischemia-reperfusion injury is one of the most common cardiac disorders leading to irreversible heart damage. Many underlying mechanisms seem to be involved, among which mitochondrial dysfunction. Since physical training has a beneficial effect on mitochondrial dynamics (fusion and fission), it may have a cardioprotective effect against IR injury also via mitochondrial pathways. This study investigates the protective role of aerobic training against cardiac IR injury and the mitochondrial dynamics as a possible mechanism.

MAIN METHODS

Thirty-two male Wistar rats (8-week old) were divided into a control, sham, control + IR, and training + IR groups (8 rats each). Training group was exercised aerobically on a treadmill for 8 weeks (5 days/week). After 8 weeks, anesthetized rats underwent a left thoracotomy (sham, control + IR, and training + IR groups) to access the left anterior descending coronary artery, which was occluded by a silk suture for 30 min and released for 90 min of reperfusion (IR groups). Triphenyltetrazolium chloride staining was used to determine the infarct size. The gene expression of mitofusin 1 (Mfn1), mitofusin 2 (Mfn2), and dynamin-related protein 1 (Drp1) was evaluated by RT-PCR. A one-way ANOVA was used for statistical analysis with the significance level set at P ≤ 0.05.

KEY FINDINGS

Cardiac infarct size was smaller In training + IR group (20.24 ± 5.7%) than in control + IR (35.9 ± 2.3%; P ≤ 0.05). Training + IR showed higher expression of Mfn1 and Mfn2 (P ≤ 0.05). Conversely, Drp1 expression was lower after training (P ≤ 0.05).

SIGNIFICANCE

Exercise-induced regulation of mitochondrial fusion and fission, leading to improvement of mitochondrial dynamics seems to be involved in the cardioprotection against IR injuries.

Skeletal muscle adiponectin induction depends on diet, muscle type/activity, and exercise modality in C57BL/6 mice

Changes in skeletal muscle adiponectin induction have been described in obesity and exercise. However, whether changes are consistent across muscle types and with different exercise modalities, remain unclear. This study compared the effects of diet and two isocaloric training programs on adiponectin induction and its regulators in three muscles: quadriceps (exercising/glycolytic-oxidative), gastrocnemius (exercising/glycolytic), and masseter (nonexercising/glycolytic). Ten-week-old male C57BL/6 mice were fed a high-fat diet (HFD) (45% fat) or standard CHOW diet (12% fat) ad libitum and underwent one of two training regimes: (1) constant-moderate training (END), or (2) high intensity interval training (HIIT) for 10 weeks (3 × 40 min sessions/week). Chow and HFD-fed untrained mice were used as control. Compared with Chow, HFD induced an increase in protein levels of low-molecular weight (LMW) adiponectin in gastrocnemius and masseter (~2-fold; P < 0.05), and a decrease of high-molecular weight adiponectin (HMW-most bioactive form) in quadriceps (~0.5-fold; P < 0.05). Only END prevented these changes (P < 0.05). HFD induced a decrease of adiponectin receptor 1 (AdipoR1) protein in exercising muscles of untrained mice (~0.5-0.8-fold; P < 0.05); notably, END also decreased AdipoR1 protein levels in lean and HFD mice. This type of training also normalized HFD-driven mRNA changes found in some adiponectin downstream factors (sirtuin 1, Pgc-1a, and Ucp2) in the three muscles tested. Our results indicate that diet, muscle type/activity, and exercise modality influences muscle adiponectin profile, and some of its mediators. These parameters should be taken into consideration when investigating this endocrine response of the skeletal muscle, particularly in the context of obesity and metabolic disorders.

Exercise protects against diabetic cardiomyopathy by the inhibition of the endoplasmic reticulum stress pathway in rats

To explore the protective effect of exercise training on the injury of myocardium tissues induced by streptozotocin (STZ) in diabetic rats and the relationship with endoplasmic reticulum stress (ERS), the male sprague‐dawley (SD) rats were fed with high‐fat and high‐sugar diet for 4 weeks, followed by intraperitoneal injection of STZ, 40 mg/kg, to establish a diabetes model, and then 10 rats were randomly selected as diabetes mellitus (DM) controls and 20 eligible diabetic rats were randomized into two groups: low‐intensity exercise training (n = 10) and high‐intensity exercise training (n = 10). After 12 weeks of exercise training, rats were killed and serum samples were used to determine cardiac troponin‐I (cTn‐I). Myocardial tissues were sampled for morphological analysis to detect myocardial cell apoptosis, and to analyze protein expression of glucose‐regulated protein 78 (GRP78), C/EBP homologous protein (CHOP), and caspase‐12. Different intensities (low and high) significantly reduced serum cTn‐I levels compared with the DCM group (p < 0.01), and significantly reduced the percentage of apoptotic myocardial cells and improved the parameters of cardiac function. Hematoxylin and eosin and Masson staining indicated that exercise training could attenuate myocardial apoptosis. Additionally, exercise training significantly reduced GRP78, CHOP, and cleaved caspase‐12 protein expression in an intensity‐dependent manner. These findings suggest that exercise appeared to ameliorate diabetic cardiomyopathy by inhibiting endoplasmic reticulum stress‐induced apoptosis in diabetic rats.

Differential metabolic effects of constant moderate versus high intensity interval training in high-fat fed mice: possible role of muscle adiponectin

Exercise regimens may have differing effects in the presence of obesity. In addition to being fat derived, adiponectin has recently been described as a myokine that regulates insulin sensitivity, which may link to exercise-related metabolic benefits in obesity. Whether skeletal muscle adiponectin varies in different exercise modalities is unclear. This study investigated the comparative effects of 10 weeks of endurance constant-moderate intensity exercise (END) with high intensity interval training (HIIT), on metabolic outcomes, including muscle adiponectin in a mouse model of diet-induced obesity. Ten-week-old male C57BL/6 mice were fed a high-fat diet (HFD) (45% FAT) or standard CHOW diet ab libitum and underwent one of three training regimes: (1) no exercise, (2) END, or (3) HIIT (8 bouts of 2.5 min with eight periods of rest of 2.5 min) for 10 weeks (3 × 40 min sessions/week). Chow-fed mice acted as controls. Compared with HFD alone, both training programs similarly protected against body weight gain (HFD = 45 ± 2; END = 37 ± 2; HIIT = 36 ± 2 g), preserved lean/fat tissue mass ratio (HFD = 0.64 ± 0.09; END = 0.34 ± 0.13; HIIT = 0.33 ± 0.13), and improved blood glucose excursion during an insulin tolerance test (HFD = 411 ± 54; END = 350 ± 57; HIIT = 320 ± 66 arbitrary units [AU]). Alterations in fasting glycemia, insulinemia, and AST/ALT ratios were prevented only by END. END, but not HIIT increased skeletal muscle adiponectin mRNA (14-fold; P < 0.05) and increased protein content of high molecular weight (HMW) adiponectin (3.3-fold), whereas HIIT induced a milder increase (2.4-fold). Compared with HFD, neither END nor HIIT altered circulating low (LMW) or high (HMW) molecular weight adiponectin forms. Furthermore, only END prevented the HFD downregulation of PGC1α (P < 0.05) mRNA levels downstream of muscle adiponectin. These data show that different training programs affect muscle adiponectin to differing degrees. Together these results suggest that END is a more effective regimen to prevent HFD-induced metabolic disturbances in mice.

Effects of age and exercise training on coronary microvascular smooth muscle phenotype and function

Coronary microvascular function and blood flow responses during acute exercise are impaired in the aged heart but can be restored by exercise training. Coronary microvascular resistance is directly dependent on vascular smooth muscle function in coronary resistance arterioles; therefore, we hypothesized that age impairs contractile function and alters the phenotype of vascular smooth muscle in coronary arterioles. We further hypothesized that exercise training restores contractile function and reverses age-induced phenotypic alterations of arteriolar smooth muscle. Young and old Fischer 344 rats underwent 10 wk of treadmill exercise training or remained sedentary. At the end of training or cage confinement, contractile responses, vascular smooth muscle proliferation, and expression of contractile proteins were assessed in isolated coronary arterioles. Both receptor- and non-receptor-mediated contractile function were impaired in coronary arterioles from aged rats. Vascular smooth muscle shifted from a differentiated, contractile phenotype to a secretory phenotype with associated proliferation of smooth muscle in the arteriolar wall. Expression of smooth muscle myosin heavy chain 1 (SM1) was decreased in arterioles from aged rats, whereas expression of phospho-histone H3 and of the synthetic protein ribosomal protein S6 (rpS6) were increased. Exercise training improved contractile responses, reduced smooth muscle proliferation and expression of rpS6, and increased expression of SM1 in arterioles from old rats. Thus age-induced contractile dysfunction of coronary arterioles and emergence of a secretory smooth muscle phenotype may contribute to impaired coronary blood flow responses, but arteriolar contractile responsiveness and a younger smooth muscle phenotype can be restored with late-life exercise training. NEW & NOTEWORTHY Aging impairs contractile function of coronary arterioles and induces a shift of the vascular smooth muscle toward a proliferative, noncontractile phenotype. Late-life exercise training reverses contractile dysfunction of coronary arterioles and restores a young phenotype to the vascular smooth muscle.

Adiponectin, orexin A and orexin B concentrations in the serum and uterine luminal fluid during early pregnancy of pigs

Adiponectin is the most abundant adipose-released protein that circulates in human plasma at high concentrations. The neuropeptides orexin A (OXA, hypocretin-1) and orexin B (OXB, hypocretin-2) are derived from a common precursor peptide, prepro-orexin and are produced mainly by neurons located in the lateral hypothalamus. It has been demonstrated that the peptides such as adiponectin and orexins have an important role in the regulation of energy metabolism and neuroendocrine functions. These hormones appear to be implicated in both normal and disturbed pregnancy. The objectives of this study were to determine adiponectin and orexin concentrations in the plasma and uterine luminal fluid (ULF) of pigs during early gestation and to explore the relationships between hormone concentrations and stages of pregnancy. The greatest plasma concentrations of adiponectin were observed on days 15-16 and 27-28 of pregnancy, and the least concentrations were on days 30-32 of gestation and on days 10-11 of the oestrous cycle. In ULF, adiponectin concentrations were greater on days 15-16 of pregnancy and on days 10-11 of the oestrous cycle than on days 10-11 and days 12-13 of pregnancy. The greatest OXA concentrations in the blood plasma were noted on days 10-16 of gestation, and the least OXA concentrations were on days 27-32 of pregnancy and on days 10-11 of the oestrous cycle. Orexin A concentrations in ULF were greater on days 10-11 of the cycle than throughout pregnancy. Serum OXB concentrations were greatest on days 10-11 and 30-32 of pregnancy, and least on days 12-28 of gestation. The greatest OXB concentrations in ULF were on days 10-13 of gestation, and the least OXB concentrations were on days 15-16 of pregnancy. This is first study to demonstrate the presence of adiponectin and orexins in the serum and ULF during early pregnancy of pigs as well as the relationships between adiponectin and orexin concentrations and the stage of pregnancy. The fluctuations in adiponectin and orexin concentrations in the plasma and ULF suggest that the hormones present in ULF are mostly of local origin and that these hormones participate in the processes that accompany early pregnancy.

Interactions of exercise training and high-fat diet on adiponectin forms and muscle receptors in mice

Background

Metabolic syndrome (MetS) is characterized by systemic disturbances that increase cardiovascular risk. Adiponectin (Ad) exhibits a cardioprotective function because of its anti-inflammatory and anti-atherosclerotic properties. In the bloodstream, this adipocytokine circulates on multimers (Ad_mer), among which high molecular weight (HMW) are the most active forms. Because alterations of Ad plasmatic levels, Ad_mer distribution and receptor (AdipoR) expression have been described in murine models and obese patients, strategies that aim to enhance Ad production or its effect on target tissues are the subject of intense investigations. While exercise training is well known to be beneficial for reducing cardiovascular risk, the contribution of Ad is still controversial. Our aim was to evaluate the effect of exercise training on Ad production, Ad_mer distribution and AdipoR muscle expression in a murine model of MetS.

Methods

At 6 weeks of age, mice were submitted to a standard (SF) or high-fat high-sugar (HF) diet for 10 weeks. After 2 weeks, the SF- and HF-fed animals were randomly assigned to a training program (SFT, HFT) or not (SFC, HFC). The trained groups were submitted to sessions of running on a treadmill 5 days a week.

Results and conclusions

The HF mice presented the key problems associated with MetS (increased caloric intake, body weight, glycemia and fat mass), a change in Ad_mer distribution in favor of the less-active forms and increased AdipoR2 expression in muscle. In contrast, exercise training reversed some of the adverse effects of a HF diet (increased glucose tolerance, better caloric intake control) without any modifications in Ad production and Ad_mer distribution. However, increased AdipoR1 muscle expression was observed in trained mice, but this effect was hampered by HF diet. These data corroborate a recent hypothesis suggesting a functional divergence between AdipoR1 and AdipoR2, with AdipoR1 having the predominant protective action on metabolic function.

Electronic supplementary material

The online version of this article (doi:10.1186/s12986-016-0138-2) contains supplementary material, which is available to authorized users.

Oxygen uptake, respiratory exchange ratio, or total distance: a comparison of methods to equalize exercise volume in Wistar rats

This study compared strategies to equalize the volume of aerobic exercise performed with different intensities by Wistar rats, based on the distance covered during exercise bouts and energy expenditure (EE, isocaloric sessions) obtained from oxygen uptake (V̇O₂) or respiratory exchange ratio (RER). Thirty-three male rats (270.5±12.8 g) underwent maximal exercise tests to determine V̇O₂ reserve (V̇O₂R), being randomly assigned to three groups: moderate-intensity continuous exercise at speed corresponding to 50% V̇O₂R (MIC; n=11); high-intensity continuous exercise at 80% V̇O₂R (HIC; n=11); and high-intensity intermittent exercise (HII; n=11) at 60% V̇O₂R (3 min) and 80% V̇O₂R (4 min). Exercise duration was calculated individually to elicit EE of 5 kcal in each session. No difference between groups was found for total running distance (MIC: 801±46, HIC: 734±42, HII: 885±64 m; P=0.13). Total EE measured by RER was systematically underestimated compared to values obtained from V̇O₂ (HII: 4.5% and MIC: 6.2%, P<0.05). Total EE (calculated from V̇O₂), and duration of HIC bouts (2.8 kcal and 30.8±2.2 min) were lower (P<0.0001) than in MIC (4.9 kcal and 64.7±1.8 min) and HII (4.7 kcal and 46.9±2.2 min). Predicted and actual values of total V̇O₂, total EE, and duration of isocaloric sessions were similar in MIC and HII (P>0.05), which were both higher than in HIC (P<0.0001). In conclusion, the time to achieve a given EE in exercise bouts with different intensities did not correspond to the total distance. Therefore, the volume of aerobic exercise in protocols involving Wistar rats should be equalized using EE rather than total covered distance.

Similar enhancement of BK(Ca) channel function despite different aerobic exercise frequency in aging cerebrovascular myocytes

Aerobic exercise showed beneficial influence on cardiovascular systems in aging, and mechanisms underlying vascular adaption remain unclear. Large-conductance Ca(2+)-activated K(+) (BK(Ca)) channels play critical roles in regulating cellular excitability and vascular tone. This study determined the effects of aerobic exercise on aging-associated functional changes in BK(Ca) channels in cerebrovascular myocytes, Male Wistar rats aged 20-22 months were randomly assigned to sedentary (O-SED), low training frequency (O-EXL), and high training frequency group (O-EXH). Young rats were used as control. Compared to young rats, whole-cell BK(Ca) current was decreased, and amplitude of spontaneous transient outward currents were reduced. The open probability and Ca(2+)/voltage sensitivity of single BK(Ca) channel were declined in O-SED, accompanied with a reduction of tamoxifen-induced BK(Ca) activation; the mean open time of BK(Ca) channels was shortened whereas close time was prolonged. Aerobic exercise training markedly alleviated the aging-associated decline independent of training frequency. Exercise three times rather than five times weekly may be a time and cost-saving training volume required to offer beneficial effects to offset the functional declines of BK(Ca) during aging.

Swimming training attenuates the morphological reorganization of the myocardium and local inflammation in the left ventricle of growing rats with untreated experimental diabetes

Diabetic cardiomyopathy is associated with cardiac remodeling, myocardial dysfunction, low-grade inflammation, and reduced cardiac adiponectin in patients with type 1 diabetes mellitus (T1DM). Alternatively, physical exercise is an important strategy for the management of diabetes. This study aimed to investigate the influence of low-intensity swimming training in cardiac cytokines, structural remodeling, and cardiomyocyte contractile dysfunction in growing rats with untreated experimental DM. Thirty-day-old male Wistar rats were divided into four groups (n=14, per group): sedentary control (SC), exercised control (EC), sedentary diabetic (SD), and exercised diabetic (ED). Diabetes was induced by streptozotocin (60 mg kg(-1), i.p.). Animals from exercised groups swam (5 days/week, 90 min/day, loading up to 5% body weight around the animal's chest) for 8 weeks. The left ventricle (LV) was removed for molecular, morphological, and cardiomyocyte mechanical analysis. Diabetic animals presented cardiac remodeling with myocardial histoarchitectural disorganization, fibrosis, and necrosis. The capillary density was lower in diabetic animals. LV cardiomyocytes from diabetic animals exhibited more prolonged time to the peak of contraction and time to half relaxation than those from control animals. The cardiac levels of interleukin 10, nitric oxide, and total and high molecular weight (HMW) adiponectin were significantly decreased in diabetic animals. Exercise training reduced the level of TNF-α, increased capillary density, and attenuated the histopathological parameters assessed in diabetic rats. In conclusion, the cardiac structural remodeling coexists with reduced levels of total and HMW adiponectin, inflammation, and cardiomyocyte contractility dysfunction in experimental DM. More important, low-intensity swimming training attenuates part of these pathological changes, indicating the beneficial role for exercise in untreated T1DM.

Nandrolone Plus Moderate Exercise Increases the Susceptibility to Lethal Arrhythmias

Background:

Until now, no experimental study has directly assessed the arrhythmogenesis of chronic consumption of anabolic androgenic steroids along with moderate-intensity endurance exercise.

Objectives:

We evaluated the influence of integration of anabolic androgenic steroids along with moderate-intensity endurance exercise on susceptibility to lethal ventricular arrhythmias in rat.

Materials and Methods:

The animal groups were as follows: control group (CTL); exercise group (EX) which were under 6 weeks of treadmill exercise; nandrolone group (Nan) which received 5 mg/kg of nandrolone decanoate twice a week; vehicle group (Arach) which received Arachis oil (solvent of nandrolone); trained vehicle group (Arach + Ex); and trained nandrolone group (Nan + Ex). One day after ending of the intervention period, arrhythmia was inducted by intravenous infusion of aconitine and ventricular arrhythmias were recorded. Then malondialdehyde (MDA) and glutathione peroxidase (GPX) of heart tissue were measured.

Results:

Nandrolone, exercise, and their combination were associated with heart hypertrophy. Exercise could prevent the incremental effect of nandrolone on MDA/GPX ratio. Chronic administration of nandrolone with moderate-intensity endurance exercise had no significant effect on blood pressure, heart rate, and basal electrocardiographic parameters. Combination of nandrolone and exercise significantly increased the incidence of ventricular fibrillation (VF) and reduced the VF latency (P < 0.05).

Conclusions:

The findings suggest that chronic coadministration of nandrolone with moderate-intensity endurance exercise facilitates the VF occurrence in rat. Complementary studies are needed to elucidate the involved mechanisms of this abnormality.

Effect of exercise intensity on unfolded protein response in skeletal muscle of rat

Endoplasmic reticulum (ER) stress, unfolded protein response (UPR), and mitochondrial biogenesis were assessed following varying intensities of exercise training. The animals were randomly assigned to receive either low- (LIT, n=7) or high intensity training (HIT, n=7), or were assigned to a control group (n=7). Over 5 weeks, the animals in the LIT were exercised on a treadmill with a 10° incline for 60 min at a speed of 20 m/min group, and in the HIT group at a speed of 34 m/min for 5 days a week. No statistically significant differences were found in the body weight, plasma triglyceride, and total cholesterol levels across the three groups, but fasting glucose and insulin levels were significantly lower in the exercise-trained groups. Additionally, no statistically significant differences were observed in the levels of PERK phosphorylation in skeletal muscles between the three groups. However, compared to the control and LIT groups, the level of BiP was lower in the HIT group. Compared to the control group, the levels of ATF4 in skeletal muscles and CHOP were significantly lower in the HIT group. The HIT group also showed increased PGC-1α mRNA expression in comparison with the control group. Furthermore, both of the trained groups showed higher levels of mitochondrial UCP3 than the control group. In summary, we found that a 5-week high-intensity exercise training routine resulted in increased mitochondrial biogenesis and decreased ER stress and apoptotic signaling in the skeletal muscle tissue of rats.

Moderate intensity exercise inhibits macrophage infiltration and attenuates adipocyte inflammation in ovariectomized rats

[Purpose]

The purpose of this study was to investigate the effects of the different endurance exercise intensities on the macrophage infiltration and adipocyte inflammation of ovariectomized rats.

[Methods]

24 female SD rats (6 weeks old) were randomly assigned to sham control (SC; n=6), ovariectomized control (OC; n=6), ovariectomized low intensity exercise (OL; n=6), and ovariectomized moderate intensity exercise (OM; n=6) groups. The two training groups ran for 60 min/day, 5 times/ week at 18 and 26m/min for 16 weeks. Twenty-four hours after the last exercise session, rats were sacrified, and epididymal pads were analyzed. F4/80 and IL-6 expressions were evaluated by western blotting. ICAM-1, VCAM-1 TLR4, TNF-α, and MCP-1 mRNA expressions were evaluated by RT-PCR.

[Results]

In comparison with OC group, OM group showed significantly lower body weight gain and adipose tissue mass. Also, OM group markedly inhibited F4/80 expression, adhesion molecule (ICAM-1, VCAM-1) and pro-inflammatory cytokines (TLR4, TNF-α, MCP-1) mRNA expressions in adipose tissue. In contrast, OL group partially prevented body weight gain while other examined parameter were unaffected by low intensity exercise training.

[Conclusion]

The results of this study suggest that OM group inhibits visceral macrophage infiltration by suppressing the adhesion molecules. It may also attenuate cytokine production in the adipose tissue by repressing the TLR4-mediated pro-inflammatory signaling cascades in ovariectomized rats.

Effect of high-fat diet on metabolic indices, cognition, and neuronal physiology in aging F344 rats

The prevalence of obesity and type 2 diabetes increases with age. Despite this, few studies have examined these conditions simultaneously in aged animals, and fewer studies have measured the impact of these conditions on brain function. Using an established animal model of brain aging (F344 rats), we investigated whether a high-fat diet (HFD) exacerbates cognitive decline and the hippocampal calcium-dependent afterhyperpolarization (a marker of age-dependent calcium dysregulation). Young and mid-aged animals were maintained on control or HFD for 4.5 months, and peripheral metabolic variables, cognitive function, and electrophysiological responses to insulin in the hippocampus were measured. HFD increased lipid accumulation in the periphery, although overt diabetes did not develop, nor were spatial learning and memory altered. Hippocampal adiponectin levels were reduced in aging animals but were unaffected by HFD. For the first time, however, we show that the AHP is sensitive to insulin, and that this sensitivity is reduced by HFD. Interestingly, although peripheral glucose regulation was relatively insensitive to HFD, the brain appeared to show greater sensitivity to HFD in F344 rats.

Low-volume exercise can prevent sucrose-induced weight gain but has limited impact on metabolic measures in rats

PURPOSE

Rats given sugar-sweetened drinks can develop glucose intolerance, insulin resistance and dyslipidaemia. The aim of this study was to investigate whether such metabolic disruptions and also possible weight gain induced by chronic sucrose consumption could be attenuated by low-volume exercise.

METHODS

Using a 2 × 2 factorial design, rats were given free access for 57 days to either a 10% sucrose solution (Suc and SucEx) or water only (Con and ConEx), while exercise rats (SucEx and ConEx) received 20-min treadmill training every 3 days. Caloric intake and body weight were measured throughout this dietary intervention. Oral glucose tolerance tests were performed on days 29 and 54. Plasma insulin, triglycerides and leptin were also measured, together with post-mortem measures of retroperitoneal fat pads and liver triglycerides.

RESULTS

In groups given sucrose, exercise reduced calorie consumption, reduced weight gain and decreased leptin relative to non-exercised controls. Exercise was found to improve glucose tolerance and insulin action at day 29, but not day 54.

CONCLUSIONS

Low-volume exercise can be effective in preventing weight gain in sucrose-fed rats, probably via reduction of subcutaneous fat, but prevention of the glucose intolerance and dyslipidaemia produced by sucrose consumption may be transient.