No difference in the lipolytic response to beta-adrenoceptor stimulation in situ but a delayed increase in adipose tissue blood flow in moderately obese compared with lean men in the postexercise period

Obesity-induced and weight-loss-induced physiological factors affecting weight regain

Weight regain after successful weight loss resulting from lifestyle interventions is a major challenge in the management of overweight and obesity. Knowledge of the causal mechanisms for weight regain can help researchers and clinicians to find effective strategies to tackle weight regain and reduce obesity-associated metabolic and cardiovascular complications. This Review summarizes the current understanding of a number of potential physiological mechanisms underlying weight regain after weight loss, including: the role of adipose tissue immune cells; hormonal and neuronal factors affecting hunger, satiety and reward; resting energy expenditure and adaptive thermogenesis; and lipid metabolism (lipolysis and lipid oxidation). We describe and discuss obesity-associated changes in these mechanisms, their persistence during weight loss and weight regain and their association with weight regain. Interventions to prevent or limit weight regain based on these factors, such as diet, exercise, pharmacotherapy and biomedical strategies, and current knowledge on the effectiveness of these interventions are also reviewed.

How to exercise to increase lipolysis and insulin sensitivity: Fasting or following a single high-protein breakfast

BACKGROUND

The purpose of this study was to investigate the lipolysis response and insulin sensitivity to high-intensity interval exercise (HIIE) upon fasting (HIIEFAST) and following the intake of a high-protein breakfast (HIIEHPFED).

METHODS

Overweight men participated in two sessions of HIIE after an overnight fast and post-HPFED with an interval of one week. Metabolic biomarkers were assessed before, immediately after, and 3h postexercise. To evaluate the metabolic effects of HIIE, two-way repeated-measures ANOVA was used.

RESULTS

Glycerol levels increased immediately after HIIEFAST and HIIEHPFED (P=0.0001) and decreased 3h after exercise in both states (P=0.001). There were no significant changes in free fatty acid (FFA) levels immediately after exercise, but a significant increase was observed 3h after exercise compared to the baseline and immediately after exercise in HIIEFAST and HIIEHPFED (P=0.0001). Insulin sensitivity was increased for 3h after HIIEHPFED compared to the baseline and immediately after exercise (P=0.04).

CONCLUSIONS

These findings suggest that fasting during exercise is not necessary for the greater stimulation of lipolysis and an increase in insulin sensitivity and that exercise following a high-protein breakfast can have a similar effect in overweight young men.

Increased Triacylglycerol Lipase Activity in Adipose Tissue of Lean and Obese Men During Endurance Exercise

CONTEXT

Although there is increasing information on the mechanism of lipolysis in adipose tissue, the effect of exercise on individual factors of lipolysis is less well understood.

OBJECTIVE

We compared changes in adipose-tissue triacylglycerol lipase activity and gene expression of adipose triacylglycerol lipase (ATGL), hormone-sensitive lipase (HSL), monoacylglycerol lipase, perilipin 1, and comparative gene identification 58 (CGI-58) during exercise between lean and obese men.

DESIGN AND PARTICIPANTS

Seven lean and nine obese men cycled for 30 minutes at a heart rate of 130 to 140 beats per minute. At baseline and 5, 10, 20, and 30 minutes of exercise, we sampled subcutaneous adipose tissue for triacylglycerol lipase activity and mRNA determination, and blood for glycerol, nonesterified fatty acid, glucose, lactate, insulin, and catecholamine determination.

SETTING

The study was conducted at a university research unit.

RESULTS

Triacylglycerol lipase activity increased at 10 minutes of exercise in the lean men and returned to baseline at 20 and 30 minutes. In the obese men, it was higher than baseline at 10, 20, and 30 minutes and higher than the corresponding values in the lean men at 20 and 30 minutes. No changes in mRNA levels were found during exercise, but the obese men had lower mRNA levels of ATGL, HSL, and CGI-58 compared with the lean men.

CONCLUSION

Our findings suggest different patterns of lipolytic stimulation during endurance exercise between lean and obese men. Differences in lipolytic rates seem to be due to differences in protein amount or activity, not mRNA levels.

Regulation of fat metabolism during resistance exercise in sedentary lean and obese men

The effect of acute resistance exercise (RE) on whole body energy expenditure (EE) and α2-adrenergic receptor (α2-AR) regulation of lipolysis in subcutaneous abdominal adipose tissue (SCAAT) was determined in sedentary lean (LN) and obese (OB) men. Lipolysis was monitored using microdialysis in 10 LN [body mass index (BMI) 20.9 ± 0.6] and 10 OB (BMI 36.2 ± 2.7) men before, during, and for 24 h after RE. EE was measured before and immediately after RE for 40 min. Changes in interstitial glycerol were measured in SCAAT with three microdialysis probes perfused with a control solution, phentolamine (α2-AR antagonist), or propranolol (β-AR antagonist). EE and fat oxidation (FOX) were significantly ( P < 0.001) elevated immediately post-RE compared with pre-RE in LN and OB subjects, with no differences between groups. RE-induced increases in SCAAT glycerol concentrations from rest to peak exercise were greater in LN than in OB men in the control (LN 142.1 ± 30.8 vs. OB 65.4 ± 14.2%, P = 0.03) and phentolamine probes (LN 187.2 ± 29.6 vs. OB 66.7 ± 11.0%, P = 0.002). Perfusion of propranolol had no effect on interstitial glycerol concentrations over the time course of the experiment in either group. Plasma insulin concentrations were significantly lower ( P = 0.002) and plasma growth hormone (GH) was significantly higher ( P = 0.03) in LN compared with OB men. The mechanism behind RE contributing to improved body composition may in part be due to enhanced SCAAT lipolysis and improved EE and FOX in response to RE in LN and OB men. The blunted SCAAT lipolytic response to RE in OB compared with LN men is unrelated to RE-induced catecholamine activation of the antilipolytic α2-ARs and may be due to depressed GH in OB subjects.

Efeitos do exercício crônico sobre a concentração circulante da leptina e grelina em ratos com obesidade induzida por dieta

A obesidade vem se tornando uma das maiores epidemias mundiais, dessa forma, conhecer sua etiologia e mecanismos que regulam seu desenvolvimento é de grande relevância para o seu Tratamento. Portanto, o objetivo do presente estudo foi avaliar os efeitos da obesidade exógena induzida pela dieta de cafeteria e da atividade física crônica em ratos, sobre a adiposidade e a concentração sérica dos hormônios reguladores do balanço energético (leptina e grelina). Foram utilizados 32 ratos Wistar machos, divididos em quatro grupos: Sedentário alimentado com dieta padrão (SN), sedentário alimentado com dieta de cafeteria (SC), treinado alimentado com dieta padrão (TN) e treinado alimentado com dieta de cafeteria (TC). A dieta de cafeteria aumentou significativamente a adiposidade central (RET) e visceral (EPI) (p<0,05), induzindo a obesidade. Por outro lado, o treinamento físico minimizou o efeito da dieta de cafeteria, diminuindo tanto a adiposidade central como a visceral. A atividade física crônica não impediu o desenvolvimento da hiperleptinemia nos ratos normocalóricos e alimentados com dieta de cafeteria. Observou-se ainda que decorrente do treinamento físico e consequente redução de massa, nos animais normocalóricos, houve diminuição na concentração plasmática de grelina. Concluímos com este estudo que a qualidade da dieta e a quantidade de tecido adiposo, apresentaram-se como importantes reguladores da concentração plasmática de hormônios reguladores do balanço energético, reforçando a importância de uma dieta adequada e da atividade física contínua na manutenção do peso corporal no combate aos efeitos deletérios da obesidade.

Effect of beta-adrenergic stimulation on whole-body and abdominal subcutaneous adipose tissue lipolysis in lean and obese men

AIMS/HYPOTHESIS

Obesity is characterised by increased triacylglycerol storage in adipose tissue. There is in vitro evidence for a blunted beta-adrenergically mediated lipolytic response in abdominal subcutaneous adipose tissue (SAT) of obese individuals and evidence for this at the whole-body level in vivo. We hypothesised that the beta-adrenergically mediated effect on lipolysis in abdominal SAT is also impaired in vivo in obese humans.

METHODS

We investigated whole-body and abdominal SAT glycerol metabolism in vivo during 3 h and 6 h [2H5]glycerol infusions. Arterio-venous concentration differences were measured in 13 lean and ten obese men after an overnight fast and during intravenous infusion of the non-selective beta-adrenergic agonist isoprenaline [20 ng (kg fat free mass)(-1) min(-1)].

RESULTS

Lean and obese participants showed comparable fasting glycerol uptake by SAT (9.7+/-3.4 vs 9.3+/-2.5% of total release, p=0.92). Furthermore, obese participants showed an increased whole-body beta-adrenergically mediated lipolytic response versus lean participants. However, their fasting lipolysis was blunted [glycerol rate of appearance: 7.3+/-0.6 vs 13.1+/-0.9 micromol (kg fat mass)(-1) min(-1), p<0.01], as was the beta-adrenergically mediated lipolytic response per unit SAT [Delta total glycerol release: 140+/-71 vs 394+/-112 nmol (100 g tissue)(-1) min(-1), p<0.05] compared with lean participants. Net triacylglycerol flux tended to increase in obese compared with lean participants during beta-adrenergic stimulation [Delta net triacylglycerol flux: 75+/-32 vs 16+/-11 nmol (100 g tissue)(-1) min(-1), p=0.06].

CONCLUSIONS/INTERPRETATION

We demonstrated in vivo that beta-adrenergically mediated lipolytic response is impaired systematically and in abdominal SAT of obese versus lean men. This may be important in the development or maintenance of increased triacylglycerol stores and obesity.

The effects of hydralazine on lipolysis in subcutaneous adipose tissue in humans

Recent evidence from animal research and in vitro experiments indicates that changes in dietary calcium intake could cause changes in lipolysis through alterations of the intracellular calcium concentration in adipocytes. The objective of the study was to examine whether the calcium antagonist hydralazine affects blood flow and lipolysis in subcutaneous abdominal adipose tissue in vivo in humans. Three different concentrations of hydralazine (12.2, 24.4, and 48.8 micromol/L) were locally administered in adipose tissue using the microdialysis technique to assess effects on lipolysis and blood flow in subcutaneous adipose tissue in the abdominal region. Subjects from the general community were studied ambulatorily at a university hospital. Eight healthy men (age, 33.1 +/- 3.3 years; body mass index, 24.2 +/- 0.2 kg/m(2)) were recruited by local announcement. Subcutaneous adipose tissue in the abdominal region was perfused with increasing concentrations of hydralazine. The main outcome measures were adipose tissue lipolysis and blood flow. Hydralazine had no effect on ethanol outflow-inflow ratios, but significantly increased interstitial glycerol concentration at the highest concentration (P < .05). The present results indicate that hydralazine increases lipolysis in abdominal subcutaneous adipose tissue in healthy lean subjects, but hydralazine had no significant effects on local blood flow in adipose tissue.

Metabolic response of trained and untrained women during high-intensity intermittent cycle exercise

The metabolic response to two different forms of high-intensity intermittent cycle exercise was investigated in young women. Subjects (8 trained and 8 untrained) performed two bouts of high-intensity intermittent exercise: short sprint (SS) (8-s sprint, 12-s recovery) and long sprint (LS) (24-s sprint, 36-s recovery) for 20 min on two separate occasions. Both workload and oxygen uptake were greater in the trained subjects but were not significantly different for SS and LS. Plasma glycerol concentrations significantly increased during exercise. Lactate concentrations rose over the 20 min and were higher for the trained women. Catecholamine concentration was also higher postexercise compared with preexercise for both groups. Both SS and LS produced similar metabolic response although both lactate and catecholamines were higher after the 24-s sprint. In conclusion, these results show that high-intensity intermittent exercise resulted in significant elevations in catecholamines that appear to be related to increased venous glycerol concentrations. The trained compared with the untrained women tended to show an earlier increase in plasma glycerol concentrations during high-intensity exercise.

Post-exercise abdominal, subcutaneous adipose tissue lipolysis in fasting subjects is inhibited by infusion of the somatostatin analogue octreotide

To determine whether blockade of the exercise-induced increase in growth hormone (GH) secretion may affect the regional lipolytic rate in the post-exercise recovery period, the aim of the present experiments was to study the effect of infusion of the somatostatin analogue octreotide on the s.c., abdominal adipose tissue metabolism, before, during and after exercise in healthy, fasting, young male subjects. The adipose tissue net releases of fatty acids and glycerol were measured by arterio-venous catheterizations and simultaneous measurements of adipose tissue blood flow with the local Xe-clearance method. Nine subjects were studied during 1-h basal rest, and then during continuous octreotide infusion during 1-h rest, 1-h exercise at 50% of maximal oxygen consumption and 4-h post-exercise rest. A control study on seven subjects was performed under similar conditions but without octreotide infusion. The results show that octreotide infusion during rest increased lipolysis and fatty acid release from the abdominal, s.c. adipose tissue. The exercise-induced increase in lipolysis and fatty acid release does not seem to be affected by octreotide when compared with the control study without octreotide infusion while the post-exercise increase in lipolysis is inhibited by octreotide, suggesting that the exercise-induced increase in GH secretion plays a role for the post-exercise lipolysis in s.c., abdominal adipose tissue.

Interactions of metabolic hormones, adipose tissue and exercise

Physiological and psychological systems work together to determine energy intake and output, and thus maintain adipose tissue. In addition, adipose tissue secretes leptin and cytokines, which induces satiety and has been linked to catecholamines, cortisol, insulin, human growth hormone, thyroid hormones, gonadotropin and lipolysis. Thus, adipose tissue is acted upon by a number of physiological stimuli, including hormones, and simultaneously, is an active component in the regulation of its own lipid content. All of the hormones mentioned above are associated with each other and respond to exercise and exercise training. Thus, exercise is one of the major links between the hormonal modulators of energy intake and output. It appears that the sympathetic nervous system and the catecholamines are key components facilitating the lipolytic activity during exercise. These two neuroendocrine factors directly affect adipose metabolism and metabolic hormones that influence adipose metabolism. Acute low- and moderate-intensity exercise causes hormonal changes that facilitate lipolytic activity. Exercise training reduces these hormonal responses, but the sensitivity to these hormones increases so that lipolysis may be facilitated. Large amounts of adipose tissue blunt the metabolic hormonal responses to exercise, but the sensitivity of these hormones is increased; thus maintaining normal lipolytic activity. Although the physiological role of the endocrine system during exercise and training is significant, other training effects may have as great, or greater influence on lipolytic activity in adipose tissue.

Effect of exercise intensity, duration and mode on post-exercise oxygen consumption

In the recovery period after exercise there is an increase in oxygen uptake termed the 'excess post-exercise oxygen consumption' (EPOC), consisting of a rapid and a prolonged component. While some studies have shown that EPOC may last for several hours after exercise, others have concluded that EPOC is transient and minimal. The conflicting results may be resolved if differences in exercise intensity and duration are considered, since this may affect the metabolic processes underlying EPOC. Accordingly, the absence of a sustained EPOC after exercise seems to be a consistent finding in studies with low exercise intensity and/or duration. The magnitude of EPOC after aerobic exercise clearly depends on both the duration and intensity of exercise. A curvilinear relationship between the magnitude of EPOC and the intensity of the exercise bout has been found, whereas the relationship between exercise duration and EPOC magnitude appears to be more linear, especially at higher intensities. Differences in exercise mode may potentially contribute to the discrepant findings of EPOC magnitude and duration. Studies with sufficient exercise challenges are needed to determine whether various aerobic exercise modes affect EPOC differently. The relationships between the intensity and duration of resistance exercise and the magnitude and duration of EPOC have not been determined, but a more prolonged and substantial EPOC has been found after hard- versus moderate-resistance exercise. Thus, the intensity of resistance exercise seems to be of importance for EPOC. Lastly, training status and sex may also potentially influence EPOC magnitude, but this may be problematic to determine. Still, it appears that trained individuals have a more rapid return of post-exercise metabolism to resting levels after exercising at either the same relative or absolute work rate; however, studies after more strenuous exercise bouts are needed. It is not determined if there is a sex effect on EPOC. Finally, while some of the mechanisms underlying the more rapid EPOC are well known (replenishment of oxygen stores, adenosine triphosphate/creatine phosphate resynthesis, lactate removal, and increased body temperature, circulation and ventilation), less is known about the mechanisms underlying the prolonged EPOC component. A sustained increased circulation, ventilation and body temperature may contribute, but the cost of this is low. An increased rate of triglyceride/fatty acid cycling and a shift from carbohydrate to fat as substrate source are of importance for the prolonged EPOC component after exhaustive aerobic exercise. Little is known about the mechanisms underlying EPOC after resistance exercise.

Lipolytic and nutritive blood flow response to beta-adrenoceptor stimulation in situ in subcutaneous abdominal adipose tissue in obese men

OBJECTIVE

beta-Adrenoceptor-mediated whole-body lipolysis is impaired in obesity. This study investigated whether local adipocyte beta-adrenergic sensitivity and changes in nutritive blood flow in subcutaneous abdominal adipose tissue contribute to this impaired response.

METHODS

Three microdialysis probes were placed in the subcutaneous abdominal adipose tissue of eight obese and nine lean men. Each probe was perfused with either 0.1, 1 and 10 microM isoprenaline; 1, 10 and 100 microM dobutamine or 1, 10 and 100 microM salbutamol, each dose for 45 min.

RESULTS

At baseline, interstitial glycerol concentrations and ethanol out/in ratios were comparable between groups. During nonselective beta-, beta(1)- and beta(2)-adrenergic stimulation, interstitial glycerol concentrations increased and ethanol out/in ratios decreased similarly in obese and lean men.

CONCLUSION

The lipolytic and nutritive blood flow response to beta(1)- beta(2)- and nonselective beta-adrenergic stimulation in situ is comparable in lean and obese male subjects. The present data suggest that a blunted beta-adrenergic sensitivity of the fat cell and an impaired local nutritive blood flow response do not contribute to the previously reported diminished whole-body beta-adrenoceptor-mediated lipolytic response in obese males.

Brain microdialysis in exercise research

During the last 5 to 10 years, the microdialysis technique has been used to explore neurotransmitter release during exercise. Microdialysis can collect virtually any substance from the brains of freely moving animals with a limited amount of tissue trauma. It allows the measurement of local neurotransmitter release in combination with ongoing behavioural changes such as exercise. Several groups examined the effect of treadmill running on extracellular neurotransmitter levels. Microdialysis probes were implanted in different brain areas to monitor diverse aspects of locomotion (striatum, hippocampus, nucleus accumbens, frontal cortex, spinal cord), food reward (hypothalamus, hippocampus, cerebral cortex), thermoregulation (hypothalamus). Some studies combined microdialysis with running on a treadmill to evaluate motor deficit and improvement following dopaminergic grafts in 6-hydroxydopamine lesioned rats, or combined proton nuclear magnetic resonance spectroscopy and cortical microdialysis to observe intra- plus extracellular brain glucose variations. This method allows us to understand neurotransmitter systems underlying normal physiological function and behaviour. Because of the growing interest in exercise and brain functioning, it should be possible to investigate increasingly subtle behavioural and physiological changes within the central nervous system. There is now compelling evidence that regular physical activity is associated with significant physiological, psychological and social benefits in the general population. In contrast with our knowledge about the peripheral adaptations to exercise, studies relating exercise to brain neurotransmitter levels are scarce. It is of interest to examine the effect of short and long term exercise on neurotransmitter release, since movement initiation and control of locomotion have been shown to be related to striatal neurotransmitter function, and one of the possible therapeutic modalities in movement, and mental disorders is exercise therapy. Until very recently most experimental studies on brain chemistry were conducted with postmortem tissue. However, in part because of shortcomings with postmortem methods, and in part because of the desire to be able to directly relate neurochemistry to behaviour, there has been considerable interest in the development of 'in vivo' neurochemical methods. Because total tissue levels may easily mask small but important neurochemical changes related to activity, it is important to sample directly in the extracellular compartment of nervous tissue in living animals. Since the chemical interplay between cells occurs in the extracellular fluid, there was a need to access this compartment in the intact brain of living and freely moving animals. Estimation of the transmitter content in this compartment is believed to be directly related to the concentration at the site where these compounds are functionally released: in the synaptic cleft. As measurements in the synapse are not yet possible, in vivo measurements in the extracellular fluid appear to provide the most directly relevant information currently available. This article provides an overview of the in vivo microdialysis technique as a method for measuring in the extracellular space, and its application in exercise science. Although this technique has been used in different tissues such as brain, adipose tissue, spinal cord and muscle, in animals as well as humans, we will focus on the use of this in vivo method in brain tissue. Recently two excellent reviews on the application of microdialysis in human experiments especially in subcutaneous tissue have been published, and we refer the interested reader to these articles.

Microdialysis in the intensive care unit: a novel tool for clinical investigation or monitoring?

Microdialysis is a minimally invasive tool that allows us to gain insight into metabolism at the tissue level. In human investigations, it can be safely performed in the brain (neurosurgical patients), skeletal muscle and adipose tissue. Basically, the technique allows interstitial concentrations of small solutes to be evaluated. Several limitations of the method and possible ways to circumvent them are indicated. Recent technical developments are reviewed. At present, this method is rarely used in metabolic monitoring of critically ill patients, but its potential applications are highlighted.

White adipocyte vascular endothelial growth factor: regulation by insulin

White adipose tissue from rats was examined for insulin- responsive vascular endothelial growth factor 165 (VEGF) secretion and mRNA expression. When separated into it constituent fat vs. stromal-vascular cells using collagenase digestion methods, only the adipocytes (or whole fat tissue) responded to physiological insulin concentrations by doubling VEGF release over 4 and 24 h in culture. Adipocyte VEGF mRNA expression increased similarly. Several adipose depots were tested. Although omental fat cells had the highest rates of VEGF release, the differences were not significant. Insulin-stimulated VEGF release was mediated in part via PI3K, but not PKC. Additional hormones/agents were tested, including steroids, leptin, an adenosine analog, and norepinephrine. Only the latter compound increased VEGF production, and this effect was mediated by adenylate cyclase. Adjusting the incubation glucose concentration between 0-20 mM did not alter adipocyte VEGF release. An experimental mimic of hypoxia, CoCl(2), also increased adipocyte VEGF, and this effect was additive with 100 nM insulin. These studies demonstrate that physiological insulin concentrations stimulate VEGF formation and expression in cultured rodent white adipocytes. Although the biological significance of this observation remains to be determined, if white adipocyte-derived VEGF has paracrine or systemic endocrine actions, these might hypothetically impact on adipose expansion or the vascular comorbidities of obesity.