European Journal of Applied Physiology

, Volume 110, Issue 2, pp 247–254

Obesity and catecholamine responses to maximal exercise in adolescent girls

Authors

    • Movement, Sport, Health and Sciences Laboratory (M2S), UFR-APSUniversity of Rennes 2-ENS Cachan
  • G. Jabbour
    • Movement, Sport, Health and Sciences Laboratory (M2S), UFR-APSUniversity of Rennes 2-ENS Cachan
    • Physiology and Biomechanics of Physical Performance Laboratory, Physical Education DepartmentUniversity of Balamand
  • H. Youssef
    • Movement, Sport, Health and Sciences Laboratory (M2S), UFR-APSUniversity of Rennes 2-ENS Cachan
  • A. Flaa
    • Cardiovascular and Renal Research Center, Department of Acute MedicineUllevaal University Hospital
  • E. Moussa
    • Physiology and Biomechanics of Physical Performance Laboratory, Physical Education DepartmentUniversity of Balamand
  • C. Groussard
    • Movement, Sport, Health and Sciences Laboratory (M2S), UFR-APSUniversity of Rennes 2-ENS Cachan
  • C. Jacob
    • Physiology and Biomechanics of Physical Performance Laboratory, Physical Education DepartmentUniversity of Balamand
Original Article

DOI: 10.1007/s00421-010-1492-9

Cite this article as:
Zouhal, H., Jabbour, G., Youssef, H. et al. Eur J Appl Physiol (2010) 110: 247. doi:10.1007/s00421-010-1492-9

Abstract

The aim of this study was to investigate plasma catecholamine [adrenaline (A) and noradrenaline (NA)] concentrations at rest and in response to maximal exercise in three different groups of adolescent girls. According to their body mass index, 34 adolescent girls aged 15–16 years were divided into three groups: a normal weight group (NO) (n = 11), an overweight group (OW) (n = 11) and an obese group (OB) (n = 12). Plasma A and NA concentrations were measured at rest during fasting conditions (A0 and NA0), after a standardized breakfast (Arest and NArest) and immediately after an incremental exhaustive exercise (AEX and NAEX). A0 and NA0 were not significantly different among the three groups. However, the A0/NA0 was statistically lower in OB compared to OW and NO. AEX and NAEX were significantly higher than resting values in the three groups. However, in response to exercise, no significant differences were reported between OB (AEX = 2.20 ± 0.13 nmol/l, NAEX = 12.28 ± 0.64 nmol/l), OW (AEX = 2.39 ± 0.23 nmol/l, NAEX = 12.94 ± 0.93 nmol/l) and NO (AEX = 2.52 ± 0.24 nmol/l, NAEX = 12.60 ± 0.63 nmol/l). In conclusion, our results showed that at rest, in adolescent girls, the responsiveness of the adrenal medulla to the sympathetic nervous activity is lower in OB subjects compared to OW and NO ones. However, in response to maximal exercise, plasma catecholamines are not affected by obesity.

Keywords

OverweightAdolescenceAdrenalineNoradrenalineMaximal oxygen uptake

Introduction

Regular physical exercise, even without decrease in body mass, elicits pronounced metabolic improvement (Björntorp 1978; Crampes et al. 2003). Muscular exercise is a condition characterized by a series of cardiovascular, endocrine and autonomic nervous system variations teleologically directed to provide an adequate energy supply to working muscles. In the post-absorptive state, this accelerated fuel flux mainly derives from glycogen and triglycerides stores. These modifications are related to exercise intensity, substrates availability and hormonal milieu (Vettor et al. 1997). Lipid mobilization during exercise is mainly dependent on an increase in sympathoadrenal activity which leads to adrenaline (A) release from the adrenal medulla and noradrenaline (NA) release from nerve endings into the circulation (Galbo et al. 1979; Jeukendrup et al. 1998; Kjaer 1998; Crampes et al. 2003).

Obesity has been shown to cause “resistance” or loss of sensitivity (loss of response per unit of hormone) for several hormones (McMurray and Hackney 2005). Obese subjects appear to have higher levels of sympathetic nervous system (SNS) activity (Troisi et al. 1991; Jones et al. 1997); however, the metabolism response to SNS stimulation appears reduced in obese individuals (Seals and Bell 2004). This suggests that in obesity any compensatory expenditure may not occur, making weight loss more difficult (Tuominen et al. 1997). In contrast to the SNS activity, circulating A levels in the obese can be either normal or reduced and the A responses to stress (e.g. hypoglycemia, exercise) are typically blunted (Del Rio 2000). Thus, catecholamine responses to exercise represent one of the common differences reported between obese and normal subjects (Del Rio 2000; McMurray and Hackney 2005; Tentolouris et al. 2006). In fact, it seems that, in adult men and women, obese exhibited significantly higher A and NA concentrations at rest and lower responses of A and NA in response to several different stimuli such as food intake (DeHaven et al. 1980; Tentolouris et al. 2006), caffeine ingestion (DeHaven et al. 1980), and physical exercise (Yale et al. 1989; Gustafson et al. 1990; Vettor et al. 1997; Del Rio 2000; Salvadori et al. 2003).

Most of metabolic and endocrine studies in the literature have dealt with adult obesity. However, childhood obesity has nowadays become a major health problem in developed countries. Not only it is a frequent and growing prevalence (Gortmaker et al. 1987; Bougnères et al. 1997), but also most obese adolescents will remain obese adults, known to be exposed to an increased risk of metabolic and vascular complications (Mossberg 1989; Must et al. 1992). Some of these complications, such as atherosclerosis, are known to be more strongly associated with juvenile than with maturity onset obesity (Must et al. 1992), suggesting that specific morbid effects could be related to early fat deposition (Bougnères et al. 1997).

Although it appears clearly in obese adults, literature concerning catecholamine responses to exercise in young obese people (especially in adolescents) are limited. To the best of our knowledge, only one study focused on A and NA responses to physical exercise in adolescent. Eliakim et al. (2006) reported significant increase of A and NA in both obese and control children (male and female) in response to ten 2-min bouts of constant-cycle ergometer above anaerobic threshold, with 1-min rest interval between each bout. However, the magnitude of the increase was significantly lower in the obese children.

The question of whether aberrations in the SNS could contribute to obesity or are just a consequence of it is an unresolved issue (Flaa et al. 2008). Studies relating to young people as adolescents can, at least in part, help answering this question in order to determine the effect of age and follow the evolution of the aberration of SNS. The importance of such studies relies upon the fact that a SNS activity may be implicated in the development of obesity.

Obesity blunts catecholamine responses to exercise in adults (Del Rio 2000; Tentolouris et al. 2006); however, the effect of obesity on these exercise-associated hormonal responses in adolescent and especially girl remains unclear. On the other hand, one can notice that the majority of the studies’ focus was to only compare catecholamine responses between obese and lean subjects omitting overweight people.

Finally, it was demonstrated that the exercise intensity plays a major role in the magnitude of catecholamine responses. As a result, the differences between groups are likely to be significant when choosing intense exercise (Zouhal et al. 2008). As being explained earlier, the aim of this study was to assess catecholamine concentrations in fasting conditions, following a standardized breakfast and maximal exercise in adolescent girls. To do so, we compared A and NA responses to maximal exercise in three groups of adolescent girls: normal group (NO), an overweight group (OW) and an obese group (OB) (Cole et al. 2000).

Materials and methods

This study was approved by the Ethical Comities of the University of Balamand and the University of Rennes 2.

Subjects

34 adolescent girls volunteered to participate in this study. According to their body’s mass index (BMI = mass [kg]/(height [m])2), they were divided into three groups: NO (n = 11, BMI = 21.55 ± 0.31 kg/m2), OW (n = 11, BMI = 26.55 ± 0.47 kg/m2), and OB (n = 12, BMI = 32.92 ± 0.64 kg/m2) (Cole et al. 2000).

Written informed consent was obtained from all participants and their parents gave written consent upon enrollment.

Anthropometric measurements

Participants came to the laboratory in the morning, after 12-h overnight fasting and they took a standardized breakfast. After medical examination, standard calibrated scales and stadiometers were used to determine height, body mass, hip and waist circumferences and BMI.

Body composition assessment by dual-energy X-ray absorptiometry (DEXA)

Since BMI does not measure lean body mass and does not invariably correlate with fat mass, body composition was also measured by DEXA using the Hologic QDR 4500 densitometer (Hologic, Bedford, MA). Subjects were scanned in light clothing, while lying down on their backs. DEXA scans were performed and analyzed using software. During the test period, the DEXA instrument was calibrated using the procedures provided by the manufacturer.

Testing procedure

One hour after breakfast, all participants performed an incremental exhaustive exercise on an electrically braked cycle ergometer (Monark: Ergomedic 839E Electronic Test Cycle) as described before by Heyman et al. (2007). Heart rate was continuously determined by an electrocardiogram (Schiller AT-102 ECG Machine, California, USA). Oxygen consumption was measured continuously by a breath-by-breath gas monitoring (Medical Graphics CPX/D, Saint Paul, MN, USA).

Blood sampling

Three blood samples from an antecubital vein were made, the first one in fasting conditions, the second 1 h after a standardized breakfast and the third one immediately at the end of the maximal test. At each extraction, the blood was collected in a vacutainer tube containing tetraacetic diamine ethylene acid (EDTA). The collected venous blood samples were immediately placed in ice. Plasma from the venous blood samples was separated by centrifugation (3,000g, 5 min, 4°C) and the aliquots of plasma were stored at −80°C for use in subsequent chemical analyses.

Biochemical analysis

Plasma catecholamine concentrations were measured by high-performance liquid chromatography (HPLC) (Chromosystems, Thermofinnigan, France), following the method of Koubi et al. (1991). Before the HPLC runs, catecholamines were extracted by selective absorption from aluminum oxide (Chromsystems-HPLC-Kit, Waters, Milford, MA, USA). The aluminum oxide was shaken up briefly with an extraction buffer (50 μl) and then 1 ml of plasma was added to 50 μl internal standard solution (600 pg dihydroxybenzylamine). The aluminum oxide was then washed three times, with a brief centrifugation between washes. The catecholamines were extracted with 120 μl elution buffer by shaking it briefly and subjecting it to a final centrifugation at 1,500g for 1 min. Then, 50 μl of the sample eluant was injected into HPLC column (Resolve TM 5 μl Sherical C 18, HPLC column, Waters) and eluted with a mobile phase. The flow rate was 1 ml/min at 13.8 mPa and a potential of 0.60 V. The chromatogram was analyzed by computer integration (Baseline 815, Waters). The detection limit of catecholamines in the described method was 0.06 nM and the inter-assay coefficient of variation was 6.5%.

The responsiveness of the adrenal medulla to the sympathetic nervous activity was estimated by the ratio A/NA as used by Kjaer (1998) and Zouhal et al. (1998).

Questionnaires

After taking the standardized breakfast, subjects answered two validated questionnaires related to quality of life (PedsQL) (Varni et al. 1999) and to physical activity (Deheeger et al. 1997). These questionnaires were proposed in their original language since all subjects were francophone. Subjects were assisted while answering. The score of physical activity was calculated as MET-hour per week (metabolic equivalent task) based on the data of Ainsworth et al. (1993) (score = intensity × duration × frequency).

One-week diet record was administered to each participant during this visit. The only instructions given to the participants before they record their dietary intake were to eat normally and not to consume any antioxidant supplements during the time period of the protocol procedure. Subjects returned the dietary record 1 week later and dietary quantification was controlled during their presence. Dietary assessment was analyzed by the same technician for caloric intake using Nutrilog 1.20b software.

Statistics

Results were expressed in mean ± SEM. Data were analyzed using Statistica 7.1 software. Normal distribution of data was tested by Kolmogorov–Smirnov test. Descriptive variables were compared between groups using an unpaired Student’s t tests for parametric data or Mann–Whitney U tests for non-parametric data. Repeated measurements were compared between groups using two-way ANOVAs (group and time) for parametric data and Wilcoxon matched pair’s tests in each group separately for non-parametric data. In addition, one-way ANOVA with trend analysis was used. In fact, the groups were selected according to their BMI, to mainly expect a linear trend in exercise responses, as well as A and NA. Pearson (parametric data) or Spearman test (non-parametric data) was used to detect correlations between variables. A value of p < 0.05 was accepted as the minimal level of statistical significance.

Results

Subjects characteristics

Table 1 reports the morphological characteristics of the three subjects’ groups. As for the anthropometric characteristics, weight and BMI, the amount of body fat, the fat-free mass, and the waist-to-hip ratio (WHR) were significantly higher in OB and OW compared to NO. These last values were also significantly higher in OB than in OW.
Table 1

Morphological characteristics, fasting lipid profile and estimated energy and macronutrients intake of the three groups, normal weight (NO), overweight (OW) and obese subjects (OB)

 

NO

OW

OB

p value between groups

NO vs. OB

OW vs. OB

NO vs. OW

Age (years)

16.92 ± 0.29

16.29 ± 0.38

16.17 ± 0.42

ns

ns

ns

Body mass (kg)

54.53 ± 1.21

68.92 ± 1.34

87.77 ± 2.46

<0.0001

<0.01

<0.01

Height (m)

1.59 ± 0.01

1.61 ± 0.01

1.63 ± 0.01

ns

ns

ns

BMI (kg/m2)

21.55 ± 0.31

26.55 ± 0.47

32.92 ± 0.64

<0.0001

<0.001

<0.01

Body fat (%)

30.13 ± 1.35

37.40 ± 1.03

41.97 ± 1.33

<0.0001

<0.001

<0.01

Fat mass (kg)

16.43 ± 1.34

25.31 ± 0.89

35.53 ± 2.12

<0.0001

<0.001

<0.01

Fat-free mass (kg)

37.35 ± 1.13

42.31 ± 0.91

48.92 ± 1.62

<0.001

<0.05

<0.05

Waist circumference (cm)

77.16 ± 1.33

89.20 ± 1.78

103.74 ± 2.62

<0.01

<0.05

ns

Hip circumference (cm)

95.97 ± 1.00

108.18 ± 1.34

121.76 ± 3.46

<0.05

ns

ns

WHR

0.79 ± 0.02

0.83 ± 0.02

0.86 ± 0.03

<0.05

ns

ns

Fasting lipid profile

 TG (mmol/l)

0.85 ± 0.19

0.83 ± 0.12

1.18 ± 0.22

<0.05

<0.05

ns

 Cholesterol (mmol/l)

3.57 ± 0.19

3.90 ± 0.23

3.43 ± 0.17

ns

ns

ns

 HDL (mmol/l)

1.33 ± 0.17

1.08 ± 0.05

1.04 ± 0.06

ns

ns

ns

 LDL (mmol/l)

1.86 ± 0.29

2.44 ± 0.21

1.84 ± 0.20

ns

ns

ns

 LDL/HDL

1.76 ± 0.28

2.38 ± 0.26

1.91 ± 0.27

ns

ns

ns

Energy and macronutrients intake

 Energy intake (kJ/day)

7,443 ± 550

8,282 ± 445

9,677 ± 330*,#

<0.05

<0.05

ns

 Protein intake (%)

14.90 ± 0.63

15.20 ± 0.61

13.80 ± 0.81

ns

ns

ns

 Lipid intake (%)

40.50 ± 1.60

39.50 ± 1.60

36.50 ± 2.31

ns

ns

ns

 Carbohydrate intake (%)

44.50 ± 1.61

45.30 ± 1.72

49.70 ± 2.82

ns

ns

ns

Values are mean ± SEM

BMI body mass index, FFM fat-free mass, FM fat mass, WHR waist-to-hip ratio, TG triglycerides, HDL high density lipoprotein, LDL low density lipoprotein, ns no significance

Fasting lipid profile

Fasting lipid profile values are listed in Table 1. Among serum lipids, only triglycerides were significantly higher in OB compared to OW and NO.

Energy and macronutrients intake

Dietary intake details are shown in Table 1. The daily caloric intake was significantly higher in OB compared to OW and NO (p < 0.05). However, there were no significant differences between the three groups concerning the average of macronutrient intake.

Exercise responses

The data about the exercise responses are presented in Table 2. No significant differences were observed between the three groups concerning exercise time. However, \( \dot{V}{\text{O}}_{{2\;{\text{peak}}}} \), expressed as absolute value, was significantly higher in OB compared to NO (p < 0.05). When \( \dot{V}{\text{O}}_{{2\;{\text{peak}}}} \)was expressed in relative value to body mass, OB showed a significantly lower value than OW (p < 0.05) and NO (p < 0.01). For the same work rate, oxygen consumption (l/min) was higher in OB, reflecting a higher energetic cost in this group.
Table 2

Resting and peak oxygen uptake (\( \dot{V}{\text{O}}_{{2\;{\text{peak}}}} \)) and performances determined during the maximal exercise of the three groups, normal weight (NO), overweight (OW) and obese subjects (OB)

 

NO

OW

OB

p value between groups

NO vs. OB

OW vs. OB

NO vs. OW

Exercise time (min.)

6.47 ± 0.27

7.26 ± 0.23

7.56 ± 0.41

ns

ns

ns

\( \dot{V}{\text{O}}_{{2\;{\text{rest}}}} \) (l/min)

0.39 ± 0.07

0.42 ± 0.06

0.39 ± 0.09

ns

ns

ns

\( \dot{V}{\text{O}}_{{2\;{\text{peak}}}} \) (l/min)

1.80 ± 0.06

2.08 ± 0.06

2.32 ± 0.05

<0.05

ns

<0.05

\( \dot{V}{\text{O}}_{{2\;{\text{peak}}}} \) (ml/min/kg)

33.22 ± 1.24

30.14 ± 0.77

26.68 ± 0.97

<0.01

<0.05

<0.05

\( \dot{V}{\text{O}}_{{2\;{\text{peak}}}} \) (ml/min/kg(FFM))

49.03 ± 2.15

48.49 ± 1.15

46.15 ± 1.65

ns

ns

ns

HR max. (bpm)

192 ± 2

190 ± 3

195 ± 2

ns

ns

ns

RQ

1.19 ± 0.05

1.11 ± 0.02

1.09 ± 0.02

ns

ns

ns

Power max. (W)

104.71 ± 2.73

120.00 ± 1.95

114.29 ± 3.88

ns

ns

ns

Power max. (W/kg)

1.93 ± 0.06

1.75 ± 0.05

1.32 ± 0.06

<0.001

<0.01

<0.05

Power max. (W/kg(FFM))

2.85 ± 0.14

2.84 ± 0.07

2.33 ± 0.10

<0.01

<0.01

ns

Values are mean ± SEM

HR heart rate (bpm), RQ respiratory quotient, W Watt, \( \dot{V}{\text{O}}_{{2\;{\text{peak}}}} \) peak oxygen uptake. ns no significance

A and NA plasma concentrations

Plasma A and NA concentrations are showed in Fig. 1a and b. A and NA at rest, during fasting conditions (A0 and NA0) and after breakfast (Arest and NArest) were not significantly different between the three groups. At the end of the exercise, AEX and NAEX were significantly higher than resting values both during fasting conditions and after breakfast in the three groups. However, no significant differences were reported between OB, OW and NO in response to maximal exercise.
https://static-content.springer.com/image/art%3A10.1007%2Fs00421-010-1492-9/MediaObjects/421_2010_1492_Fig1_HTML.gif
Fig. 1

Plasma adrenaline (a) and noradrenaline (b) concentrations determined in fasting conditions, before exercise, after breakfast and at the end of the maximal test

For the delta values of A and NA [e.g. from rest (fasting conditions or after breakfast) to exercise], there were no significant differences between our three groups.

Several relationships were observed in our study between plasma catecholamine concentrations and other parameters: for OW group, significant relationships between A0 and energy intake (kcal/day) (r = 0.71, p < 0.05), Arest and energy intake (kcal/day) (r = 0.59, p < 0.05), Arest and cholesterol (mg/dl) (r = 0.68, p < 0.05), Arest and LDL (mg/dl) (r = 0.62, p < 0.05), AEX and energy intake (kcal/day) (r = 0.73, p < 0.05); for OB group, significant relationships between A0 and body fat (%) (r = −0.58, p < 0.05), A0 and lipid intake (kcal/day) (r = −0.87, p < 0.05), Arest and cholesterol (mg/dl) (r = 0.60, p < 0.05), AEX and cholesterol (mg/dl) (r = 0.45, p < 0.05).

Discussion

The main findings in our study are that plasma catecholamine (A and NA) concentrations were not statistically different between normal weight, overweight and obese adolescent girls both at rest, during fasting conditions, not just only after breakfast but also in response to maximal exercise. These results differ from those observed in adult.

Maximal oxygen uptake

Our results show that for comparative exercise duration using the same power output, in absolute value, obese girls consumed more oxygen and consequently had higher energetic cost (\( \dot{V}{\text{O}}_{2} /{\text{power}} \)). This result is in accordance with the literature data that showed that obese subjects use greater amount of O2 to accomplish an equal external work rate when compared to normal subjects (Wasserman 1994) because their increased body mass requires a greater metabolic energy exchange (Whipp and Davis 1984). Hence, when peak oxygen uptake (\( \dot{V}{\text{O}}_{{2\;{\text{peak}}}} \)) is related to body weight, OB group exhibited significantly lower values than OW and NO groups. This result is often explained by the excessive weight and the additive mechanical work required swinging legs that have a greater mass and moment of inertia (Duché et al. 2002).

Catecholamine responses at rest and in response to maximal exercise

Catecholamines are known to increase when experiencing heavy exercise, in part because of central nervous system mechanisms. Activation of the hypothalamic-pituitary axis and sympathetic-adrenal-medullary activation leads to A release from the adrenal medulla and NA from nerve endings into the circulation (Pedersen and Hoffman-Goetz 2000; Van Loon 1983). Thus, the ratio A/NA can be considered as an index of the adrenal medulla responses to the sympathetic nervous activity (Kjaer 1998; Zouhal et al. 1998; Zouhal et al. 2008). Maximal exercise could also lead to an increase of plasma A and NA concentrations more than does submaximal exercise or other stimuli (Zouhal et al. 1998).

At rest, during fasting conditions and after the breakfast, plasma A and NA concentrations were similar between our three groups NO, OW and OB. These results were in the same way of those observed in normal adolescent girls (Botcazou et al. 2006a, b) and in obese young girls and boys (Eliakim et al. 2006) and suggest that obesity had no effect on catecholamine responses at rest in adolescent girls.

In response to exercise, plasma A and NA concentrations increased markedly and significantly in our three groups NO, OW and OB. The increase in sympathoadrenal activity is the most important autonomic neuroendocrine responses during exercise (Bülow and Simonsen 1993). For our three groups, plasma A and NA concentrations measured in our study at the end of maximal exercise were higher than those measured in other studies also in adolescent subjects in response to short sprint exercise (Botcazou et al. 2006b) and to intermittent submaximal exercise (Eliakim et al. 2006). These divergences can, at least in part, be explained by the intensity of the exercise which was higher in our study. Indeed, the intensity of the exercise may induce more stress which leads to increasing catecholamine output (Zouhal et al. 2008).

Our results show that the increase in plasma A and NA concentrations was similar between our three groups NO, OW and OB. These results suggest strongly that obesity had no effect on A and NA responses to maximal exercise in adolescent girls. To the best of our knowledge, only one study conducted in adolescent subjects observed significant differences in catecholamine responses to exercise (Eliakim et al. 2006). In fact, these authors, in response to ten 2-min bouts of constant-cycle ergometry above the anaerobic threshold, with 1-min rest interval between each bout observed significantly higher plasma A and NA in normal weight (n = 25, 12.8 ± 0.5 years) than in obese subjects (n = 25, 12.8 ± 0.5 years). However, in that study, both normal group and obese group were composed by girls and boys and we have no results by gender. Moreover, catecholamine responses to exercise are known to be altered by the gender. In fact, both at rest and in response to several stimuli such as physical exercise, A and NA responses remain different according to the gender (Zouhal et al. 2008).

On the other hand, our results here differ from those observed in obese adult subjects. Indeed, it is often observed that obese adult subjects exhibited significantly lower responses of plasma A and NA to several different stimuli such as food intake (DeHaven et al. 1980; Tentolouris et al. 2006), caffeine ingestion (Tentolouris et al. 2006), and physical exercise (Yale et al. 1989; Vettor et al. 1997; Gustafson et al. 1990; Del Rio 2000; Salvadori et al. 2003). As being different from adult data, it is no doubt that with aging (e.g. history of obesity) blunting neuroadrenergic, pathways can simultaneously decrease catecholamine responses to several stimuli such as physical exercise (Eliakim et al. 2006).

In humans, the role of the SNS in obesity is less clear. In our study, several interesting relationships were observed both in OW and OB groups between catecholamine and % body fat or other obesity factors such as cholesterol or % food intake. In the same way, Petersen et al. (1988) have reported a negative correlation between body fat and plasma NA levels and suggested that decreased sympathetic activity may be a cause of obesity. More recently, Flaa et al. (2008) reported important results from a longitudinal study conducted during 18 years in Caucasian subjects. Their results indicate that A activity during mental stress is a negative predictor of BMI, waist circumference and triceps skinfold thickness after 18 years of follow-up. Bougnères et al. (1997) observed that in vivo lipolysis, which mostly reflects the mobilization of lipid stores from subcutaneous adipose tissue, shows a decreased sensitivity to A in childhood onset obesity. Their results suggest that in obese children (12.1 ± 0.1 years) during the dynamic phase of fat accumulation, the observed resistance to catecholamine might possibly be causative rather than the result of obesity (Bougnères et al. 1997).

In conclusion, our study showed clearly that plasma A and NA levels determined at rest, during fasting conditions after breakfast, and following a maximal exercise were not affected by obesity in adolescent girls. These findings will contribute to the ongoing debate concerning the relation between obesity and sympathoadrenal activity.

Endurance training is known to increase catecholamine responses both at rest and in response to other stimuli such as physical exercise. Consequently, a program of endurance training may prevent the decrease of catecholamine responses in obese adolescents.

Acknowledgments

We are grateful for the cooperation and participation of the adolescents and their parents.

Conflict of interest statement

The authors declare no conflict of interest.

Copyright information

© Springer-Verlag 2010