Sex differences in lipolysis-regulating mechanisms in overweight subjects: effect of exercise intensity

Objective: To explore sex differences in the regulation of lipolysis during exercise, the lipid‐mobilizing mechanisms in the subcutaneous adipose tissue (SCAT) of overweight men and women were studied using microdialysis. Research Methods and Procedures: Subjects matched for age, BMI, and physical fitness performed two 30‐minute exercise bouts in a randomized fashion: the first test at 30% and 50% of their individual maximal oxygen uptake (Vo _2max) and the second test at 30% and 70% of their Vo _2max. Results: In both groups, an exercise‐dependent increment in extracellular glycerol concentration (EGC) was observed. Whatever the intensity, phentolamine [α‐adrenergic receptor (AR) antagonist] added to a dialysis probe potentiated exercise‐induced lipolysis only in men. In a probe containing phentolamine plus propranolol (β‐AR antagonist), no changes in EGC occurred when compared with the control probe when exercise was performed at 30% and 50% Vo _2max. A significant reduction of EGC (when compared with the control probe) was observed in women at 70% Vo _2max. At each exercise power, the plasma non‐esterified fatty acid and glycerol concentrations were higher in women. Exercise‐induced increase in plasma catecholamine levels was lower in women compared with men. Plasma insulin decreased and atrial natriuretic peptide increased similarly in both groups. Discussion: Overweight women mobilize more lipids (assessed by glycerol) than men during exercise. α₂‐Anti‐lipolytic effect was functional in SCAT of men only. The major finding is that during low‐to‐moderate exercise periods (30% and 50% Vo _2max), lipid mobilization in SCAT relies less on catecholamine‐dependent stimulation of β‐ARs than on an increase in plasma atrial natriuretic peptide concentrations and the decrease in plasma insulin.     

Activation of alpha(2)-adrenergic receptors impairs exercise-induced lipolysis in SCAT of obese subjects

With the use of the microdialysis method, exercise-induced lipolysis was investigated in subcutaneous adipose tissue (SCAT) in obese subjects and compared with lean ones, and the effect of blockade of alpha(2)-adrenergic receptors (ARs) on lipolysis during exercise was explored. Changes in extracellular glycerol concentrations and blood flow were measured in SCAT in a control microdialysis probe at rest and during 60-min exercise bouts (50% of heart rate reserve) and in a probe supplemented with the alpha(2)-AR antagonist phentolamine. At rest and during exercise, plasma norepinephrine and epinephrine concentrations were not different in obese compared with lean men. In the basal state, plasma and extracellular glycerol concentrations were higher, whereas blood flow was lower in SCAT of obese subjects. During exercise, the increase of plasma glycerol was higher in obese subjects (115 +/- 35 vs. 65 +/- 21 micromol/l). Oppositely, the exercise-induced increase in extracellular glycerol concentrations in SCAT was five- to sixfold lower in obese than in lean subjects (50 +/- 14 vs. 318 +/- 53 micromol/l). The exercise-induced increase in extracellular glycerol concentration was not significantly modified by phentolamine infusion in lean subjects but was strongly enhanced in the obese subjects and reached the concentrations found in lean sujects (297 +/- 46 micromol/l). These findings demonstrate that the physiological stimulation of SCAT adipocyte alpha(2)-ARs during exercice-induced sympathetic nervous system activation contributes to the blunted lipolysis noted in obese men.     

Atrial natriuretic peptide contribution to lipid mobilization and utilization during head-down bed rest in humans

Head-down bed rest (HDBR) increases plasma levels of atrial natriuretic peptide (ANP) and decreases norepinephrine levels. We previously demonstrated that ANP promotes lipid mobilization and utilization, an effect independent of sympathetic nervous system activation, when infused into lean healthy men at pharmacological doses. The purpose of the present study was to demonstrate that a physiological increase in ANP contributes to lipid mobilization and oxidation in healthy young men. Eight men were positioned for 4 h in a sitting (control) or in a HDBR position. Indexes of lipid mobilization and hormonal changes were measured in plasma. Extracellular glycerol, an index of lipolysis, was determined in subcutaneous adipose tissue (SCAT) with a microdialysis technique. A twofold increase in plasma ANP concentration was observed after 60 min of HDBR, and a plateau was maintained thereafter. Plasma norepinephrine decreased by 30-40% during HDBR, while plasma insulin and glucose levels did not change. The level of plasma nonesterified fatty acids was higher during HDBR. SCAT lipolysis, as reflected by interstitial glycerol, as well as interstitial cGMP, the second messenger of the ANP pathway, increased during HDBR. This was associated with an increase in blood flow observed throughout HDBR. Significant changes in respiratory exchange ratio and percent use of lipid and carbohydrate were seen only after 3 h of HDBR. Thus the proportion of lipid oxidized increased by 40% after 3 h of HDBR. The rise in plasma ANP during HDBR was associated with increased lipolysis in SCAT and whole body lipid oxidation. In this physiological setting, independent of increasing catecholamines, our study suggests that ANP contributes to lipid mobilization and oxidation in healthy young men.     

Lack of alpha(2)-adrenergic antilipolytic effect during exercise in subcutaneous adipose tissue of trained men.

The aim of this study was to investigate the involvement of the antilipolytic alpha(2)-adrenergic receptor pathway in the regulation of lipolysis during exercise in subcutaneous abdominal adipose tissue (SCAAT). Seven trained men and 15 untrained men were studied. With the use of microdialysis, the extracellular glycerol concentration was measured in SCAAT at rest and during 60 min of exercise at 50% of maximal oxygen consumption. One microdialysis probe was perfused with Ringer solution; the other was supplemented with phentolamine (alpha(2)-adrenergic receptor antagonist). No differences in baseline extracellular or plasma glycerol concentrations were found between the two groups. The exercise-induced extracellular and plasma glycerol increase was higher in trained compared with untrained subjects (P < 0.05). Addition of phentolamine to the perfusate enhanced the exercise-induced response of extracellular glycerol in untrained subjects but not in trained subjects. The exercise-induced increase in plasma norepinephrine and epinephrine concentrations and the decrease in plasma insulin were not different in the two groups. These in vivo findings demonstrate higher exercise-induced lipolysis in trained compared with untrained subjects and show that, in trained subjects, the alpha(2)-mediated antilipolytic action is not involved in the regulation of lipolysis in SCAAT during exercise.     

Adipose tissue lipolysis is increased during a repeated bout of aerobic exercise.

The goal of the study was to examine whether lipid mobilization from adipose tissue undergoes changes during repeated bouts of prolonged aerobic exercise. Microdialysis of the subcutaneous adipose tissue was used for the assessment of lipolysis; glycerol concentration was measured in the dialysate leaving the adipose tissue. Seven male subjects performed two repeated bouts of 60-min exercise at 50% of their maximal aerobic power, separated by a 60-min recovery period. The exercise-induced increases in extracellular glycerol concentrations in adipose tissue and in plasma glycerol concentrations were significantly higher during the second exercise bout compared with the first (P < 0.05). The responses of plasma nonesterified fatty acids and plasma epinephrine were higher during the second exercise bout, whereas the response of norepinephrine was unchanged and that of growth hormone lower. Plasma insulin levels were lower during the second exercise bout. The results suggest that adipose tissue lipolysis during aerobic exercise of moderate intensity is enhanced when an exercise bout is preceded by exercise of the same intensity and duration performed 1 h before. This response pattern is associated with an increase in the exercise-induced rise of epinephrine and with lower plasma insulin values during the repeated exercise bout.     

Exercise-induced lipid mobilization in subcutaneous adipose tissue is mainly related to natriuretic peptides in overweight men

Involvement of sympathetic nervous system and natriuretic peptides in the control of exercise-induced lipid mobilization was compared in overweight and lean men. Lipid mobilization was determined using local microdialysis during exercise. Subjects performed 35-min exercise bouts at 60% of their maximal oxygen consumption under placebo or after oral tertatolol [a beta-adrenergic receptor (AR) antagonist]. Under placebo, exercise increased dialysate glycerol concentration (DGC) in both groups. Phentolamine (alpha-AR antagonist) potentiated exercise-induced lipolysis in overweight but not in lean subjects; the alpha(2)-antilipolytic effect was only functional in overweight men. After tertatolol administration, the DGC increased similarly during exercise no matter which was used probe in both groups. Compared with the control probe under placebo, lipolysis was reduced in lean but not in overweight men treated with the beta-AR blocker. Tertatolol reduced plasma nonesterified fatty acids and insulin concentration in both groups at rest. Under placebo or tertatolol, the exercise-induced changes in plasma nonesterified fatty acids, glycerol, and insulin concentrations were similar in both groups. Exercise promoted a higher increase in catecholamine and ANP plasma levels after tertatolol administration. In conclusion, the major finding of our study is that in overweight men, in addition to an increased alpha(2)-antilipolytic effect, the lipid mobilization in subcutaneous adipose tissue that persists during exercise under beta-blockade is not dependent on catecholamine action. On the basis of correlation findings, it seems to be related to a concomitant exercise-induced rise in plasma ANP when exercise is performed under tertatolol intake and a decrease in plasma insulin.     

Catecholamine and insulin control of lipolysis in subcutaneous adipose tissue during long-term diet-induced weight loss in obese women

The aim of this study was to investigate the evolution of the adrenergic and insulin-mediated regulation of lipolysis during different phases of a 6-mo dietary intervention. Eight obese women underwent a 6-mo dietary intervention consisting of a 1-mo very low-calorie diet (VLCD) followed by a 2-mo low-calorie diet (LCD) and 3-mo weight maintenance (WM) diet. At each phase of the dietary intervention, microdialysis of subcutaneous adipose tissue (SCAT) was performed at rest and during a 3-h hyperinsulinemic euglycemic clamp. Responses of dialysate glycerol concentration (DGC) were determined at baseline and during local perfusions with adrenaline or adrenaline and phentolamine before and during the last 30 min of the clamp. Dietary intervention induced a body weight reduction and an improved insulin sensitivity. DGC progressively decreased during the clamp, and this decrease was similar during the different phases of the diet. The adrenaline-induced increase in DGC was higher at VLCD and LCD compared with baseline condition and returned to prediet levels at WM. In the probe with adrenaline and phentolamine, the increase in DGC was higher than that in the adrenaline probe at baseline and WM, but it was not different at VLCD and LCD. The results suggest that the responsiveness of SCAT to adrenaline-stimulated lipolysis increases during the calorie-restricted phases due to a reduction of the α(2)-adrenoceptor-mediated antilipolytic action of adrenaline. At WM, adrenaline-stimulated lipolysis returned to the prediet levels. Furthermore, no direct relationship between insulin sensitivity and the diet-induced changes in the regulation of lipolysis was found.     

Tocopherol mobilization during dynamic exercise after beta-adrenergic blockade.

This study addresses the question of whether tocopherol mobilization during exercise could be explained by a lipolysis effect. Nine healthy male subjects were submitted to dynamic exercise of graded intensity (45, 60, 75% VO2max) on a cycle ergometer after ingestion of either a placebo or 40 mg propranolol as beta-blocker. Plasma tocopherol concentration increased toward a peak value reached during or at the end of exercise. The magnitude of this increase did not differ in the two experimental conditions while plasma free fatty acids concentration was lowered under beta-adrenergic blockade by propranolol. From these results, we conclude that tocopherol mobilization during dynamic exercise does not depend on lipolysis.     

Natriuretic peptides: a new lipolytic pathway in human fat cells

Human fat cell lipolysis was considered until recently to be an exclusive cAMP/protein-kinase A (PKA)-regulated metabolic pathway under the control of catecholamines and insulin. Moreover, exercise-induced lipid mobilization in humans was considered to mainly depend on catecholamine action and interplay between fat cell beta- and alpha2-adrenergic receptors controlling adenylyl cyclase activity and cAMP production. We have recently demonstrated that natriuretic peptides stimulate lipolysis and contribute to the regulation of lipid mobilization in humans. Atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP) stimulate lipolysis in human isolated fat cells. Activation of the adipocyte plasma membrane type A guanylyl cyclase receptor (NPR-A), increase in intracellular guanosine 3',5'-cyclic monophosphate (cyclic GMP) levels and activation of hormone-sensitive lipase mediate the action of ANP. ANP does not modulate cAMP production and PKA activity. Increment of cGMP induces the phosphorylation of hormone-sensitive lipase and perilipin A via the activation of a cGMP dependent protein kinase-I (cGK-I). Plasma concentrations of glycerol and non-esterified fatty acids are increased by i.v. infusion of ANP in humans. Physiological relevance of the ANP-dependent pathway was demonstrated in young subjects performing physical exercise. ANP plays a role in conjunction with catecholamines in the control of exercise-induced lipid mobilization. This pathway becomes of major importance when subjects are submitted to chronic treatment with a beta-blocker. Oral beta-adrenoceptor blockade suppresses the beta-adrenergic component of catecholamine action in fat cells and potentiates exercise-induced ANP release by the heart. These findings may have several implications whenever natriuretic peptide secretion is altered such as in subjects with left ventricular dysfunction, congestive heart failure and obesity.     

Influence of lipolysis and fatty acid availability on fuel selection during exercise

The aim of the present study was to investigate the influence of substrate availability on fuel selection during exercise. Eight endurance-trained male cyclists performed 90-min exercise at 70 % of their maximal oxygen uptake in a cross-over design, either in rested condition (CON) or the day after 2-h exercise practised at 70 % of maximal oxygen uptake (EX). Subjects were given a sucrose load (0.75 g kg^?1 body weight) 45 min after the beginning of the 90-min exercise test. Lipolysis was measured in subcutaneous abdominal adipose tissue (SCAT) by microdialysis and substrate oxidation by indirect calorimetry. Lipid oxidation increased during exercise and tended to decrease during sucrose ingestion in both conditions. Lipid oxidation was higher during the whole experimental period in the EX group (p?=?0.004). Interestingly, fuel selection, assessed by the change in respiratory exchange ratio (RER), was increased in the EX session (p?=?0.002). This was paralleled by a higher rate of SCAT lipolysis reflected by dialysate glycerol, plasma glycerol, and fatty acids (FA) levels (p?<?0.001). Of note, we observed a significant relationship between whole-body fat oxidation and dialysate glycerol in both sessions (r ²?=?0.33, p?=?0.02). In conclusion, this study highlights the limiting role of lipolysis and plasma FA availability to whole-body fat oxidation during exercise in endurance-trained subjects. This study shows that adipose tissue lipolysis is a determinant of fuel selection during exercise in healthy subjects.     

Are blood flow and lipolysis in subcutaneous adipose tissue influenced by contractions in adjacent muscles in humans?

Aerobic exercise increases whole body adipose tissue lipolysis, but is lipolysis higher in subcutaneous adipose tissue (SCAT) adjacent to contracting muscles than in SCAT adjacent to resting muscles? Ten healthy, overnight-fasted males performed one-legged knee extension exercise at 25% of maximal workload (W(max)) for 30 min followed by exercise at 55% W(max) for 120 min with the other leg and finally exercised at 85% W(max) for 30 min with the first leg. Subjects rested for 30 min between exercise periods. Femoral SCAT blood flow was estimated from washout of (133)Xe, and lipolysis was calculated from femoral SCAT interstitial and arterial glycerol concentrations and blood flow. In general, blood flow and lipolysis were higher in femoral SCAT adjacent to contracting than adjacent to resting muscle (time 15-30 min; blood flow: 25% W(max) 6.6 +/- 1.0 vs. 3.9 +/- 0.8 ml x 100 g(-1) x min(-1), P < 0.05; 55% W(max) 7.3 +/- 0.6 vs. 5.0 +/- 0.6 ml x 100 g(-1) x min(-1), P < 0.05; 85% W(max) 6.6 +/- 1.3 vs. 5.9 +/- 0.7 ml x 100 g(-1) x min(-1), P > 0.05; lipolysis: 25% W(max) 102 +/- 19 vs. 55 +/- 14 nmol x 100 g(-1) x min(-1), P = 0.06; 55% W(max) 86 +/- 11 vs. 50 +/- 20 nmol x 100 g(-1) x min(-1), P > 0.05; 85% W(max) 88 +/- 31 vs. -9 +/- 25 nmol x 100 g(-1) x min(-1), P < 0.05). In conclusion, blood flow and lipolysis are generally higher in SCAT adjacent to contracting than adjacent to resting muscle irrespective of exercise intensity. Thus specific exercises can induce "spot lipolysis" in adipose tissue.     

Effect of beta-adrenergic blockade on lipid mobilization induced by fasting in dogs

To evaluate the contribution of catecholamines to the fasting-induced lipid mobilization prolonged or acute blockade of beta-adrenergic receptors with propranolol was applied in dogs during 72 hrs of food withdrawal. Propranolol given orally in a dose of 15 mg twice daily throughout the whole period of fasting failed to modify the increases in the plasma FFA and glycerol concentrations. The acute beta-adrenergic blockade due to i.v. injection of propranolol (0.5 mg/kg b.w.) caused marked decreases in the plasma glycerol concentration both in the dogs fasting for 24 h and 72 hrs, whereas the effects of propranolol on the plasma FFA concentration was found only in the early stage of fasting. Plasma catecholamine concentrations were enhanced significantly by the 72 hrs food withdrawal and neither prolonged nor acute propranolol administration modified significantly this effect. The fasting-induced decreases in the serum insulin concentration were more pronounced in dogs treated with propranolol. Results of this study indicate that catecholamines are involved in the control of lipolysis during short term starvation. However, under these conditions beta-adrenergic blockade did not impair FFA mobilization most probably due to an enhanced contribution of other hormones to the control of this process.     

Physiological and pathophysiological features of the control of lipolysis and lipid mobilization by natriuretic peptides

We have demonstrated a potent and specific lipolytic effect of natriuretic peptides (NP) in human and primates' fat cells. The lipolytic effect of NP is mediated through intracellular production of cGMP and activation of the cGMP-dependent kinase 1alpha. Local infusion of atrial-NP (ANP), directly within the subcutaneous adipose tissue through a microdialysis catheter, increases lipolysis and stimulates blood flow through its vasodilating effect in lean healthy men. This effect is blunted in overweight men and can be recovered by endurance training. Intravenous infusion of physiological doses of ANP induces lipid mobilization. Higher concentrations of ANP that are encountered during heart failure also stimulate lipid oxidation. ANP activates lipolysis and free fatty acids release from adipose tissue during endurance exercise. This effect is paradoxically amplified when exercise is performed under beta-blockade treatment, because of an enhanced cardiac release of ANP. No gender differences in ANP-induced lipid mobilization during exercise have been found. Heart failure is associated with high circulating levels of NP that could participate to the progression toward cachexia. On contrary, a negative correlation between NP levels and body mass index is found in obese persons. The molecular basis of this inverse correlation is not yet demonstrated from a functional standpoint. Further studies are needed to clearly define the pathophysiological role of NP in obesity and heart failure.     

Adrenergic control of lipolysis and metabolic responses in obesity

Adrenergic modulation of lipolysis was determined in obese and lean women. Epinephrine was infused alone, or in combination with propranolol, or with phentolamine. In both obese and lean subjects slight alpha- and prevalent beta-adrenergic lipolytic responsiveness was observed. alpha-adrenergic blockade by yohimbine potentiated lipolysis and exercise energy expenditure. Yohimbine application during the slimming treatment increased weight loss without side effects.     

Characterization of lipolytic responses of isolated white adipocytes from hamsters.

1. Lipolysis by isolated white adipocytes from hamsters, as measured by glycerol production, was stimulated by corticotropin, isopropylnorepinephrine (INE), norepinephrine, or epinephrine (EPI), in a dose-dependent fashion. 2. Lipolysis was stimulated by five inhibitors of cyclic 3',5'-adenosine monophosphate phosphodiesterase: caffeine, theophylline, 1-methyl-3-isobutyl xanthine, 1-ethyl-4-(isopropylidenehydrazine)-1H-pyrazolo-(3,4,-b)-pyridine-5-carboxylic acid ethyl ester (SQ 20009), and 4-(3,4-dimethoxybenzyl)-2-imidazolidinone (Ro 7-2956). Caffeine-stimulated lipolysis consistently attained higher rates than did hormone-stimulated lipolysis. However, when cells were stimulated by both caffeine and a hormone, lipolytic rates were consistently lower than those attained under the influence of caffeine alone. 3. Isolated white adipocytes from hamsters were sensitive to both alpha- and beta-adrenergic antagonists. The beta-adrenergic antagonist propranolol could completely inhibit norepinephrine-stimulated glycerol production. The alpha-adrenergic antagonist phentolamine, on the other hand, had a biphasic effect on the cells. At 5-10(-7) M or 5-10(-6) M, phentolamine enhanced norepinephrine-stimulated lipolysis, while concentrations higher than 5-10(-5) M caused inhibition. 4. The effects of two different concentrations of six antilipolytic agents, prostaglandin E1, nicotinic acid, phenylisopropyladenosine, 5-methylpyrazole-3-carboxylic acid, adenosine and insulin, were measured. With the exception of insulin, all of these agents showed much more potent inhibition of caffeine-stimulated lipolysis than of hormone-stimulated lipolysis. Insulin, in contrast, showed only modest inhibition of hormone-stimulated lipolysis and virtually no inhibition of caffeine-stimulated lipolysis.     

Aerobic training improves exercise-induced lipolysis in SCAT and lipid utilization in overweight men

The aim of this study was to investigate whether endurance training improves lipid mobilization and oxidation in overweight subjects. Eleven young men (25.6 +/- 1.4 yr and body mass index 27.7 +/- 0.2) performed a 4-mo training program consisting of practicing aerobic exercise 5 days/wk. Before and after the training period, lipid oxidation was explored during a 60-min exercise at 50% of peak O2 consumption by use of indirect calorimetry. Lipid mobilization and antilipolytic alpha2-adrenoceptor effect were also studied using the microdialysis method in abdominal subcutaneous adipose tissue (SCAT). After training, plasma nonesterified fatty acid (NEFA) levels, at rest and during exercise, were significantly lower than before (P < 0.001). Lipolysis in SCAT was significantly higher after than before training. An antilipolytic alpha2-adrenoceptor effect in SCAT was underlined during exercise before training and disappeared after. The respiratory exchange ratio was lower after training, i.e., the percentage of lipid oxidation was higher only at rest. The amount of lipid oxidized was higher after training, at rest, and during exercise. Although exercise power was higher after training, the relative intensity was equivalent, as suggested by a similar increase in plasma catecholamine concentrations before and after training. In conclusion, 4-mo training in overweight men improved lipid mobilization through a decrease of antilipolytic alpha2-adrenoceptor effect in SCAT and lipid oxidation during moderate exercise. Training induced a decrease of blood NEFA, predicting better prevention of obesity.     

Enhancement of fat metabolism by repeated bouts of moderate endurance exercise.

This study compared the fat metabolism between "a single bout of prolonged exercise" and "repeated bouts of exercise" of equivalent exercise intensity and total exercise duration. Seven men performed three trials: 1) a single bout of 60-min exercise (Single); 2) two bouts of 30-min exercise, separated by a 20-min rest between exercise bouts (Repeated); and 3) rest. Each exercise was performed with a cycle ergometer at 60% of maximal oxygen uptake. In the Single and Repeated trials, serum glycerol, growth hormone, plasma epinephrine, and norepinephrine concentrations increased significantly (P<0.05) during the first 30-min exercise bout. In the Repeated trial, serum free fatty acids (FFA), acetoacetate, and 3-hydroxybutyrate concentrations showed rapid increases (P<0.05) during a subsequent 20-min rest period. During the second 30-min exercise bout, FFA and epinephrine responses were significantly greater in the Repeated trial than in the Single trial (P<0.05). Moreover, the Repeated trial showed significantly lower values of insulin and glucose than the Single trial. During the 60-min recovery period after the exercise, FFA, glycerol, and 3-hydroxybutyrate concentrations were significantly higher in the Repeated trial than in the Single trial (P<0.05). The relative contribution of fat oxidation to the energy expenditure showed significantly higher values (P<0.05) in the Repeated trial than in the Single trial during the recovery period. These results indicate that repeated bouts of exercise cause enhanced fat metabolism compared with a single bout of prolonged exercise of equivalent total exercise duration.     

Lack of antilipolytic effect of lactate in subcutaneous abdominal adipose tissue during exercise.

The purpose of our study was to evaluate the potential inhibition of adipose tissue mobilization by lactate. Eight male subjects (age, 26. 25 +/- 1.75 yr) in good physical condition (maximal oxygen uptake, 59.87 +/- 2.77 ml. kg-1. min-1; %body fat, 10.15 +/- 0.89%) participated in this study. For each subject, two microdialysis probes were inserted into abdominal subcutaneous tissue. Lactate (16 mM) was perfused via one of the probes while physiological saline only was perfused via the other, both at a flow rate of 2.5 microl/min. In both probes, ethanol was also perfused for adipose tissue blood flow estimation. Dialysates were collected every 10 min during rest (30 min), exercise at 50% maximal oxygen consumption (120 min), and recovery (30 min) for the measurement of glycerol concentration. During exercise, glycerol increased significantly in both probes. However, no differences in glycerol level and ethanol extraction were observed between the lactate and control probes. These findings suggest that lactate does not impair subcutaneous abdominal adipose tissue mobilization during exercise.     

The lipid-mobilizing effect of atrial natriuretic peptide is unrelated to sympathetic nervous system activation or obesity in young men

We recently demonstrated that natriuretic peptides and especially the atrial natriuretic peptide (ANP) are powerful lipolytic agents on isolated human fat cells. To search for a possible influence of obesity on ANP responsiveness, we compared the lipolytic effects of human ANP (h-ANP) on isolated subcutaneous abdominal adipose tissue (SCAAT) fat cells from young healthy lean and obese men. The lipid-mobilizing effects of an intravenous infusion of h-ANP was studied, as well as various metabolic and cardiovascular parameters that were compared in the same subjects. h-ANP (50 ng/min/kg) was infused iv for 60 min. Microdialysis probes were inserted in SCAAT to measure modifications of the extracellular glycerol concentrations during h-ANP infusion. Spectral analysis of blood pressure and heart rate oscillations that were recorded using digital photoplethysmography were used to assess changes in autonomic nervous system activity. h-ANP induced a marked and similar increase in glycerol and nonesterified fatty acids, and a weak increase in insulin plasma levels in lean and obese men. Plasma norepinephrine concentrations rose similarly during h-ANP infusion in lean and obese men. The effects of h-ANP infusion on the autonomic nervous system were similar in both groups, with an increase in the spectral energy of the low-frequency band of systolic blood pressure variability and a decrease in the spectral energy of the high-frequency band of heart rate. In SCAAT, h-ANP infusion increased extracellular glycerol concentration and decreased blood flow similarly in both groups. The increase in extracellular glycerol observed during h-ANP infusion was not modified when 0.1 mM propranolol was added to the microdialysis probe perfusate to prevent beta-adrenoceptor activation. These data show that ANP is a potent lipolytic hormone independent of the activation of the sympathetic nervous system, and that obesity did not modify the lipid-mobilizing effect of ANP in young obese subjects.     

Circulating immunoreactive proANP1-30 and proANP31-67 responses to acute exercise

The circulating immunoreactive atrial natriuretic peptide (C-terminal; alpha-ANP) increases during exercise to become suppressed in the first hours of the recovery. The response of the N-terminal ANP fragments to acute exercise is not known while proANP (31-67) appears to be elevated with chronic exercise. We evaluated the plasma concentrations of the N-terminal ANP fragments (1-30) and (31-67) in oarsmen (n=10) before and after two acute exercise bouts separated by 5 h. As control, measurements were made on a day with no exercise (n=12). At rest, the concentrations of proANP(1-30) and proANP(31-67) were 344+/-42 and 810+/-172 pmol x l(-1), respectively. Half an hour after the first exercise bout, proANP(1-30) was elevated (to 404+/-48 pmol x l(-1); P<0.05) and decreased below the pre-exercise level (to 316+/-41 pmol x l(-1); P<0.05) 4 h into the recovery period. Also, 30 min after the second exercise session, the concentration of proANP(1-30) was elevated to 408+/-45 pmol x l(-1) (P<0.05) and the pre-exercise level was re-established on the following morning. Thus, proANP(1-30), rather than proANP(31-67), responded to acute exercise. These results suggest that atrial distension and, therefore, the central blood volume changes markedly in athletes during a day with repeated exercise bouts.