Sympathetic Activity Assessed during Exercise Recovery in Young Obese Females.

OBJECTIVE: To evaluate differences in sympathetic activity, as assessed by an exercise recovery index (ERI; heart rate/oxygen consumption [VO2] plateau), between black and white obese female adolescents. An additional aim was to determine the association of ERI with insulin resistance (homeostasis model assessment of insulin resistance [HOMA-IR]), cardiovascular fitness per fat-free mass (VO2 per fat-free mass), systolic blood pressure (SBP), and percent body fat (%FAT) in both black and white obese adolescents. STUDY DESIGN: Sixty-one females volunteered to participate in this study. HOMA-IR, SBP, and %FAT were assessed during resting conditions in black (n = 49, 13.7 ± 1.6 years, 38.1 ± 6.1 kg/m(2)) and white (n = 12, 13.3 ± 2.2 years, 34.3 ± 4.9 kg/m(2)) obese adolescents. An ERI was calculated during a 5-minute passive recovery period immediately following a graded treadmill exercise test to exhaustion. RESULTS: The ERI was significantly greater in black compared with white obese adolescent females (29.8 ± 6.4 vs 24.1 ± 3.1 bpm·mLO2(-1)·min(-1), P = .004). Using multiple linear regression modeling, there was a significant independent association between ERI and VO2 per fat-free mass (r = -0.310, P = .027) and %FAT (r = 0.326, P = .020) in black obese adolescents after controlling for HOMA-IR and SBP. CONCLUSIONS: These results suggest that black obese adolescent females have greater sympathetic activity, as assessed by an ERI, than white obese adolescent females. These findings support the need for weight management efforts aimed at both reducing %FAT and improving fitness in obese adolescents, specifically black females. TRIAL REGISTRATION: Registered with Clinicaltrials.gov: NCT00562293.

Sex differences in pulmonary oxygen uptake kinetics in obese adolescents.

OBJECTIVE: To determine whether sex differences exist in the pulmonary oxygen uptake (VO2) uptake on-kinetic response to moderate exercise in obese adolescents. We also examined whether a relationship existed between the VO2 on-transient response to moderate intensity exercise, steady-state VO2, and peak VO2 between obese male and female adolescents. STUDY DESIGN: Male (n = 12) and female (n = 28) adolescents completed a graded exercise test to exhaustion on a treadmill. Data from the initial 4 minutes of treadmill walking were used to determine the time constant. RESULTS: The time constant was significantly different (P = .001) between obese male and female adolescents (15.17 ± 8.45 seconds vs 23.07 ± 8.91 seconds, respectively). No significant relationships were observed between the time constant and variables of interest in either sex. CONCLUSIONS: Sex differences exist in VO2 uptake on-kinetics during moderate exercise in obese adolescents, indicating an enhanced potential for male subjects to deliver and/or use oxygen. It may be advantageous for female subjects to engage in a longer warm-up period before the initiation of an exercise regimen to prevent an early termination of the exercise session.

G protein-coupled receptor kinase-2 in peripheral blood mononuclear cells following acute mental stress.

AIMS: This study investigated G-protein-coupled receptor kinase-2 (GRK2) density in peripheral blood mononuclear cells (PBMC) and its relationship to plasma pro-inflammatory cytokine concentrations following acute mental stress. MAIN METHODS: Apparently healthy males (n=20; 21.3±0.55years) participated in an acute mental stress task. Heart rate was measured at baseline and throughout mental stress. Plasma epinephrine (EPI), norepinephrine (NE), tumor necrosis factor-alpha (TNF-α) and interleukin-6 (IL-6) were assessed via enzyme-linked immunosorbent assays before, immediately following, and 30, 60 and 120min after the mental stress task. GRK2 density was measured by western blot technique at the same time points. KEY FINDINGS: Acute mental stress elicited significant elevations in HR, and plasma EPI and NE. Additionally, GRK2 density increased significantly across time following the stress task. Post hoc analyses revealed that GRK2 density was significantly elevated at 30 and 60min following acute stress. A significant positive correlation was observed between GRK2 density and plasma EPI, while a significant negative correlation was revealed between GRK2 density and TNF-α across all time points. SIGNIFICANCE: Acute mental stress significantly increased GRK2 density in PBMCs of young adult males. Furthermore, although plasma IL-6 and TNF-α did not change following mental stress, it remains unknown whether a longer time period was needed to observe a pro-inflammatory state associated with the desensitization of ß-adrenergic receptor activity. Our findings that GRK2 expression is promptly increased in PBMC following an acute stress task, may suggest a link between stress and intracellular inflammatory signaling.

The effect of acute physical and mental stress on soluble cellular adhesion molecule concentration.

AIMS: This study investigated the impact of acute physical and mental stress on serum concentrations of vascular cell adhesion molecule (VCAM)-1 and CX3CL1/fractalkine. MATERIALS AND METHODS: Male volunteers (n=20; 21.3±0.55years of age) completed a graded treadmill test to exhaustion and a 20-minute mental stress task (Stroop Color-Word Test, mental arithmetic) on separate, non-consecutive days. Heart rate (HR) was measured at baseline and throughout exercise and mental stress. Blood was collected at baseline (PRE), immediately following (POST) and 30min after (POST30) exercise and mental stress. Soluble VCAM-1 and fractalkine were quantified in participant serum via enzyme-linked immunosorbent assays. KEY FINDINGS: Both treadmill exercise and the mental stress task significantly increased participant HR; although, exercise resulted in a substantially greater increase in participant HR compared to mental stress (197.82±11.99 vs. 38.67±3.10% [p<0.001]). VCAM-1 (815.74±139.55 vs. 738.67±131.59ng/mL [p=0.002]) and fractalkine (1.032±0.33 vs. 0.59±0.20ng/mL [p<0.001]) were significantly elevated in participant serum POST maximal exercise before returning to values similar to baseline at POST30. The acute mental stress task did not significantly alter serum VCAM-1 or fractalkine at any time point. SIGNIFICANCE: In conclusion, maximal aerobic exercise results in a significant elevation of the soluble adhesion molecules VCAM-1 and fractalkine in the serum of adult males that does not occur following laboratory-induced mental stress. The findings of the current investigation may suggest a novel protective role for acute aerobic exercise in vascular health via exercise-induced CAM proteolysis.