Acute effects of high fat and high glucose meals on the growth hormone response to exercise

Molecular Interactions between Dietary Lipids and Bone Tissue during Aging

Age-related bone disorders such as osteoporosis or osteoarthritis are a major public health problem due to the functional disability for millions of people worldwide. Furthermore, fractures are associated with a higher degree of morbidity and mortality in the long term, which generates greater financial and health costs. As the world population becomes older, the incidence of this type of disease increases and this effect seems notably greater in those countries that present a more westernized lifestyle. Thus, increased efforts are directed toward reducing risks that need to focus not only on the prevention of bone diseases, but also on the treatment of persons already afflicted. Evidence is accumulating that dietary lipids play an important role in bone health which results relevant to develop effective interventions for prevent bone diseases or alterations, especially in the elderly segment of the population. This review focuses on evidence about the effects of dietary lipids on bone health and describes possible mechanisms to explain how lipids act on bone metabolism during aging. Little work, however, has been accomplished in humans, so this is a challenge for future research.

Aspects of inflammation and oxidative stress in pediatric obesity and type 1 diabetes: an overview of ten years of studies

Obesity and type 1 diabetes (T1DM) are the two most common conditions of altered metabolism in children and adolescents. In both, similar long-term cardiovascular complications are known to occur, mediated in large part by underlying inflammatory and oxidative processes whose biochemical details remain relatively unclear. Through a series of experiments in these patient populations, over the last decade our laboratory has clarified a number of key issues in this field. Interestingly, while obese and type 1 diabetic children often differed in the specific type and magnitude of molecular alterations, in both groups a clear exaggeration of inflammatory and oxidative activation was detected when compared to healthy, age-matched controls. Our main findings include definition of resting and exercise-induced cytokine patterns and leukocyte profiles, patterns of activation of immune cells in vitro, and correlation of the magnitude of observed alterations with severity of obesity and quality of glycemic control. Further, we have identified a series of alterations in growth factor profiles during exercise that parallel inflammatory changes in obese children. This paper offers a concise overview of the salient results from this decade-long research effort.

Synergistic effect of obesity and lipid ingestion in suppressing the growth hormone response to exercise in children

Diet plays an important role in modulating exercise responses, including activation of the growth hormone (GH)/insulin-like growth factor-I (IGF-1) axis. Obesity and fat ingestion were separately shown to reduce exercise GH responses, but their combined effect, especially important in children, has not been studied. We therefore measured the GH response to exercise [30-min intermittent cycling, ten 2-min bouts at ~80% maximal aerobic capacity (Vo(2max)), separated by 1-min rest], started 45 min after ingestion of a high-fat meal (HFM) in 16 healthy [controls; body mass index percentile (BMI%ile) 51 ± 7], and 19 obese (Ob, BMI%ile 97 ± 0.4) children. Samples were drawn at baseline (premeal), and at start, peak, and 30 min postexercise. In the Ob group, a marked ~75% suppression of the GH response (ng/ml) to exercise was observed (2.4 ± 0.6 vs. 10.6 ± 2.1, P < 0.001). This level of suppression was also significantly greater compared with age-, fitness-, and BMI-matched historical controls that had performed identical exercise in fasting conditions. Our data indicate that the reduction in the GH response to exercise, already present in obese children vs. healthy controls, is considerably amplified by ingestion of fat nutrients shortly before exercise, implying a potentially downstream negative impact on growth factor homeostasis and long-term modulation of physiological growth.

Dose-dependent relationship between severity of pediatric obesity and blunting of the growth hormone response to exercise

In children, exercise modulates systemic anabolism, muscle growth, and overall physiological development through the growth hormone (GH)-insulin-like growth factor I (IGF-I) axis. GH secretion, at rest and during exercise, changes with age and maturational status and can be blunted by hyperlipidemia and obesity, with possible negative effects on physiological growth. However, little is known about the effect of progressively more severe pediatric obesity on the GH response to exercise and its relationship to pubertal status. We therefore studied 48 early- or late-pubertal obese children [body mass index (BMI) >95th percentile, separated in tertiles with progressively greater BMI] and 42 matched controls (BMI <85th percentile), who performed ten 2-min cycling bouts at approximately 80% of maximal O2 consumption, separated by 1-min rest intervals. Plasma GH and IGF-I were measured at baseline and end exercise. GH responses were systematically blunted in obese children, with more pronounced blunting paralleling increasing BMI. Although overall the GH response to exercise was greater in late-pubertal than in younger children, this blunting pattern was observed in early- and late-pubertal children. Our results reveal insight into the interaction between pediatric obesity and key modulators of physiological growth and development and underscore the necessity of optimizing physical activity strategies for specific pediatric dysmetabolic conditions.

Skeletal muscle growth in young rats is inhibited by chronic exposure to IL-6 but preserved by concurrent voluntary endurance exercise

Childhood diseases are often accompanied by chronic inflammation, which is thought to negatively impact growth. Interleukin-6 (IL-6) is typically cited as an indicator of inflammation and is linked to impaired growth. This study was designed to isolate and identify potential effects of chronic IL-6 exposure on skeletal muscle growth during development. A second aim was to determine if endurance exercise, thought to antagonize chronic inflammation, would interact with any effects of IL-6. The muscles of one leg of rapidly growing rats were exposed to IL-6 or vehicle for 14 days. Subgroups of IL-6-infused rats were provided access to running wheels. Local IL-6 infusion resulted in approximately 13% muscle growth deficit (myofibrillar protein levels). Exercise (>4,000 m/day) prevented this deficit. IL-6 infusion increased mRNA for suppressor of cytokine signaling-3 (SOCS3) and tumor necrosis factor-alpha (TNF-alpha), and this was not prevented by exercise. IL-6 infusion increased the mRNAs for atrogin, insulin-like growth factor-I (IGF-I), and IGF binding protein-4 (IGFBP4), and these effects were mitigated by exercise. Exercise stimulated an increase in total RNA ( approximately 19%) only in the IL-6-infused muscle, suggesting that a compensatory increase in translational capacity was required to maintain muscle growth. This study indicates that IL-6 exposure during periods of rapid growth in young animals can retard growth possibly via interactions with key growth factors. Relatively high volumes of endurance-type exercise do not exacerbate the negative effects of IL-6 and in fact were found to be beneficial in protecting muscle growth.

The growth hormone response to repeated bouts of sprint exercise with and without suppression of lipolysis in men

A single 30-s sprint is a potent physiological stimulus for growth hormone (GH) release. However, repeated bouts of sprinting attenuate the GH response, possibly due to negative feedback via elevated systemic free fatty acids (FFA). The aim of the study was to use nicotinic acid (NA) to suppress lipolysis to investigate whether serum FFA can modulate the GH response to exercise. Seven nonobese, healthy men performed two trials, consisting of two maximal 30-s cycle ergometer sprints separated by 4 h of recovery. In one trial (NA), participants ingested NA (1 g 60 min before, and 0.5 g 60 and 180 min after sprint 1); the other was a control (Con) trial. Serum FFA was not significantly different between trials before sprint 1 but was significantly lower in the NA trial immediately before sprint 2 [NA vs. Con: mean (SD); 0.08 (0.05) vs. 0.75 (0.34) mmol/l, P < 0.05]. Peak and integrated GH were significantly greater following sprint 2 compared with sprint 1 in the NA trial [peak GH: 23.3 (7.0) vs. 7.7 (11.9) microg/l, P < 0.05; integrated GH: 1,076 (350) vs. 316 (527) microg.l(-1).60 min(-1), P < 0.05] and compared with sprint 2 in the Con trial [peak GH: 23.3 (7.0) vs. 5.2 (2.3) microg/l, P < 0.05; integrated GH: 1,076 (350) vs. 206 (118) microg.l(-1).60 min(-1), P < 0.05]. In conclusion, suppressing lipolysis resulted in a significantly greater GH response to the second of two sprints, suggesting a potential role for serum FFA in negative feedback control of the GH response to repeated exercise.

Determinants of oxygen uptake. Implications for exercise testing

For exercise modalities such as cycling which recruit a substantial muscle mass, muscle oxygen uptake (VO2) is the primary determinant of pulmonary VO2. Indeed, the kinetic complexities of pulmonary VO2 associated with exercise onset and the non-steady state of heavy (> lactate threshold) and severe [> asymptote of power-time relationship for high intensity exercise (W)] exercise reproduce with close temporal and quantitative fidelity those occurring across the exercising muscles. For moderate (< lactate threshold) exercise and also rapidly incremental work tests, pulmonary (and muscle) VO2 increases as a linear function of work rate (approximately equal to 9 to 11 ml O2/W/min) in accordance with theoretical determinations of muscle efficiency (approximately equal to 30%). In contrast, for constant load exercise performed in the heavy and severe domains, a slow component of the VO2 response is manifest and pulmonary and muscle VO2 increase as a function of time as well as work rate beyond the initial transient associated with exercise onset. In these instances, muscle efficiency is reduced as the VO2 cost per unit of work becomes elevated, and in the severe domain, this VO2 slow component drives VO2 to its maximum and fatigue ensues rapidly. At pulmonary maximum oxygen uptake (VO2max) during cycling, the maximal cardiac output places a low limiting ceiling on peak muscle blood flow, O2 delivery and thus muscle VO2. However, when the exercise is designed to recruit a smaller muscle mass (e.g. leg extensors, 2 to 3kg), mass-specific muscle blood flow and VO2 at maximal exercise are 2 to 3 times higher than during conventional cycling. consequently, for any exercise which recruits more than approximately equal to 5 to 6kg of muscle at pulmonary VO2max, there exists a mitochondrial or VO2 reserve capacity within the exercising muscles which cannot be accessed due to oxygen delivery limitations. The implications of these latter findings relate to the design of exercise tests. Specifically, if the purpose of exercise testing is to evaluate the oxidative capacity of a small muscle mass (< 5 to 6kg), the testing procedure should be designed to restrict the exercise to those muscles so that a central (cardiac output, muscle O2 delivery) limitation is not invoked. It must be appreciated that exercise which recruits a greater muscle mass will not stress the maximum mass-specific muscle blood flow and VO2 but rather the integration of central (cardiorespiratory) and peripheral (muscle O2 diffusing capacity) limitations.

Effect of two beta 2-agonist drugs, salbutamol and broxaterol, on the growth hormone response to exercise in adult patients with asthmatic bronchitis

The aim of our study was to evaluate the effect of the iv administration of two different beta 2- receptors agonists, salbutamol and broxaterol, on the growth hormone (GH) response to maximal exercise in 11 patients (8 males and 3 females; age range 18-65 yr; mean +/- SE age 56 +/- 13 yr; BMI 26.2 +/- 1.4 kg/m2) with chronic asthmatic bronchitis. All the subjects underwent four cycloergometric exercise tests (incremental workload until maximal predicted heart rate). At baseline, at maximal exercise, at the end of the recovery period and 60 min after the end of each exercise, blood samples were drawn for the assay of GH, glucose, insulin, lactates, norepinephrine and epinephrine. Two exercises were performed without treatment while the remaining two were performed 60 min after the administration of 400 micrograms of either salbutamol or broxaterol (both diluted in 10 ml of saline) according to a randomized double blind cross-over design. Both exercise tests performed without treatment caused a significant (p < 0.05) and similar GH peak with respect to baseline values (from 0.3 +/- 0.1 micrograms/L to 2.8 +/- 1.3 micrograms/L, mean of the two exercise tests). Salbutamol pretreatment blunted the GH response to exercise which caused a no more significant serum GH peak over the baseline levels (from 0.6 +/- 0.2 micrograms/L to 1.4 +/- 0.6 micrograms/L,). Moreover, broxaterol completely abolished the GH response to exercise (baseline level 0.6 +/- 0.2 micrograms/L; peak levels 0.4 +/- 0.1 micrograms/L). The serum GH peak after exercise + broxaterol was significantly (p < 0.05) lower as compared to exercise + salbutamol. In conclusion, we have demonstrated for the first time that beta 2 stimulation blunts the physiological GH response to maximal exercise in adult human subjects. It can be suggested that changes in brain neurotransmitters, possibly an increase in the alpha-adrenergic tone, are likely to be involved in this endocrine effects of exercise.