The hormonal response to exercise

The hypothalamic regulation of metabolic adaptations to exercise

Our modern lifestyle is characterised by easy access to nutrient dense foods combined with limited physical activity. A sedentary lifestyle is one of several factors that have contributed to the global obesity epidemic and it also predisposes to chronic illnesses such as diabetes and cardiovascular disease. Although many studies have focused on the benefits of exercise in peripheral tissues, the contributions of the central nervous system to these exercise-induced metabolic adaptations are relatively unknown. The present review highlights the role of the ventromedial hypothalamus in regulating the metabolic response to exercise.

Difference of catecholamine responses to exercise in men with trisomy 21, with or without chronotropic incompetence

OBJECTIVE

Our purpose was to analyse if catecholamine responses to exercise would be different in Down syndrome (DS) with or without chronotropic incompetence.

RESEARCH DESIGN AND METHODS

Twenty five men with DS (mean age 22.2 ± 3.2) and twenty six controls (CONT, mean age 22.5 ± 1.4) participated in the study, and are divided into 3 groups: CONT, DS with chronotropic incompetence (DS+) and DS without chronotropic incompetence (DS-). During two treadmill incremental tests, blood samples were collected for the determination of hormonal and metabolic variables.

RESULTS

Ten out of 25 DS had chronotropic incompetence whereas no CONT. At rest, compared to CONT, despite similar physical activity, DS with chronotropic incompetence had significantly higher subcutaneous fat mass (p<0.001), lower epinephrine concentration (p<0.01), and higher leptin (p<0.01) and insulin concentrations (p<0.05). At peak exercise, all DS had lower heart rate, oxygen uptake and blood lactate concentrations than controls (p<0.001). During a 'Submaximal incremental test', DS with chronotropic incompetence had lower HR and lactate values (p<0.001) compared to CONT and DS without chronotropic incompetence (p<0.01). They also had blunted epinephrine and impaired norepinephrine responses to exercise compared to DS without chronotropic incompetence and CONT (p<0.01 and p<0.05 respectively).

CONCLUSIONS

Our results indicate that catecholamine adaptations to exercise are not adequate in DS+ and are associated with exercise intolerance. Thus, this endocrine profile at rest and during exercise may limit endurance performance of DS.

Different responses of selected hormones to three types of exercise in young men

Exercise is a potent stimulus for release of growth hormone (GH), cortisol, testosterone and prolactin, and prolonged exercise inhibits insulin secretion. These responses seem to be specific to the type of exercise but this has been poorly characterised primarily because they have not been compared during exercise performed by the same individuals. We investigated hormone responses to resistance, sprint and endurance exercise in young men using a repeated measures design in which each subject served as their own control. Eight healthy non-obese young adults (18-25 years) were studied on four occasions in random order: 30-s cycle ergometer sprint (Sprint), 30-min resistance exercise bout (Resistance), 30-min cycle at 70 % VO(2max) (Endurance), and seated rest in the laboratory (Rest). Cortisol, GH, testosterone, prolactin, insulin and glucose concentrations were measured for 60 min after the four different interventions. Endurance and sprint exercise significantly increased GH, cortisol, prolactin and testosterone. Sprint exercise also increased insulin concentrations, whereas this decreased in response to endurance exercise. Resistance exercise significantly increased only testosterone and glucose. Sprint exercise elicited the largest response per unit of work, but the smallest response relative to mean work rate in all hormones. In conclusion, the nature and magnitude of the hormone response were influenced by exercise type, perhaps reflecting the roles of these hormones in regulating metabolism during and after resistance, sprint and endurance exercise.

Exercise intensity modulation of hepatic lipid metabolism

Lipid metabolism in the liver is complex and involves the synthesis and secretion of very low density lipoproteins (VLDL), ketone bodies, and high rates of fatty acid oxidation, synthesis, and esterification. Exercise training induces several changes in lipid metabolism in the liver and affects VLDL secretion and fatty acid oxidation. These alterations are even more conspicuous in disease, as in obesity, and cancer cachexia. Our understanding of the mechanisms leading to metabolic adaptations in the liver as induced by exercise training has advanced considerably in the recent years, but much remains to be addressed. More recently, the adoption of high intensity exercise training has been put forward as a means of modulating hepatic metabolism. The purpose of the present paper is to summarise and discuss the merit of such new knowledge.

Food-dependent, exercise-induced gastrointestinal distress

Among athletes strenuous exercise, dehydration and gastric emptying (GE) delay are the main causes of gastrointestinal (GI) complaints, whereas gut ischemia is the main cause of their nausea, vomiting, abdominal pain and (blood) diarrhea. Additionally any factor that limits sweat evaporation, such as a hot and humid environment and/or body dehydration, has profound effects on muscle glycogen depletion and risk for heat illness. A serious underperfusion of the gut often leads to mucosal damage and enhanced permeability so as to hide blood loss, microbiota invasion (or endotoxemia) and food-born allergen absorption (with anaphylaxis). The goal of exercise rehydration is to intake more fluid orally than what is being lost in sweat. Sports drinks provide the addition of sodium and carbohydrates to assist with intestinal absorption of water and muscle-glycogen replenishment, respectively. However GE is proportionally slowed by carbohydrate-rich (hyperosmolar) solutions. On the other hand, in order to prevent hyponatremia, avoiding overhydration is recommended. Caregiver's responsibility would be to inform athletes about potential dangers of drinking too much water and also advise them to refrain from using hypertonic fluid replacements.

The impact of physical exercise on the gastrointestinal tract

PURPOSE OF REVIEW

Physical exercise can be both beneficial and harmful for the gastrointestinal tract in a dose-effect relationship between its intensity and health. Mild-to-moderate intensity exercises play a protective role against colon cancer, diverticular disease, cholelithiasis and constipation, whereas acute strenuous exercise may provoke heartburn, nausea, vomiting, abdominal pain, diarrhea and even gastrointestinal bleeding. This review focuses on mechanisms involved in those symptoms and their associations with type of exercises in humans.

RECENT FINDINGS

One quarter to one half of elite athletes are hampered by the gastrointestinal symptoms that may deter them from participation in training and competitive events. Vigorous exercise-induced gastrointestinal symptoms are often attributed to altered motility, mechanical factor or altered neuroimmunoendocrine secretions. Training, lifestyle modifications, meal composition, adequate hydration and avoidance of excessive use of some medications are the recommendations.

SUMMARY

Strenuous exercise and dehydrated states would be the causes of gastrointestinal symptoms referred by 70% of the athletes. Gut ischemia would be the main cause of nausea, vomiting, abdominal pain and (bloody) diarrhea. The frequency is almost twice as high during running than during other endurance sports as cycling or swimming and 1.5-3.0 times higher in the elite athletes than the recreational exercisers.

Are hormonal responses to exercise in young men with Down's syndrome related to reduced endurance performance?

The aim of the present study was to analyse whether hormonal responses could explain an exercise limitation in Down's syndrome (DS). Fourteen young men with DS (mean age 22.5 +/- 0.7 years) and 15 controls (CONT, mean age 22.5 +/- 0.3 years) participated in the study. During a treadmill submaximal incremental test, blood samples were collected for determination of hormonal and metabolic variables. Compared to CONT, DS individuals showed lower VO(2max) (P < 0.05), and lower duration of submaximal incremental exercise (P < 0.001). At rest, DS individuals showed greater catecholamines, insulin and leptin values (P < 0.05), but lower testosteronemia and cortisolemia (P < 0.05), compared to CONT. During submaximal incremental tests, catecholamines and cortisol were not increased, whereas the insulin concentration of DS individuals was significantly higher (P < 0.01) compared to CONT. Glycaemia increased significantly at the end of submaximal incremental test for CONT but not for DS individuals (P < 0.01). Maximal fat oxidation was lower (P < 0.01), whereas non-esterified fatty acids concentrations rose significantly during submaximal exercise in DS individuals. These results indicate an altered hormonal response to exercise in DS individuals. This endocrine profile at rest and during exercise may limit endurance performance in DS individuals.

Abuse of growth hormone among young athletes

The underground abuse of growth hormone (GH) among young athletes presents a challenge to medical professionals. Health care professionals providing knowledgeable guidance regarding healthy ways to improve performance and appearance, as well as accurate information regarding substances' perceived benefits, risks, and unknown qualities, is invaluable to the young athlete. Further research focused on the profile and motivation of young people who use GH is essential to understanding and intervening better with those who use these substances.

Increased Plasma Levels of Growth Hormone, Insulin-Like Growth Factor (IGF)-I and IGF-Binding Protein 3 in Pregnant Rats with Exercise

Growth hormone (GH) and insulin-like growth factor-I (IGF-I) are closely related molecules. Insulin-like growth factor-binding protein-3 (IGFBP-3) is a main molecule that binds IGF-I. GH, IGF-I and IGFBP-3 have important roles in growth and development. In this study, we investigated the effects of exercise during pregnancy on maternal plasma levels of GH, IGF-I and IGFBP-3 and on fetal development. We also recorded the weights of placenta, lengths of umbilical cord, fetal body weights, fetal heights, and weights of fetal tissues. Pregnant Wistar Albino rats were divided into two groups: exercise and control groups (n = 7 for each). A treadmill exercise was performed as 20 m/min for 20 min/day, once per day for 19 days in exercise group. Blood samples were collected from pregnant rats on 0, 7th, 14th and 20th days of gestation (D) under anesthesia with intracardiac puncture, and maternal plasma levels of GH, IGF-I and IGFBP-3 were determined. Fetuses were taken with cesarean section on D20, and various parameters for fetal growth were measured. Plasma GH and IGF-I levels were elevated in exercising pregnant rats on D14 and D20, respectively, when compared to controls, and IGFBP-3 levels were increased on D14 and D20. Among the growth parameters examined, only fetal body weights and weights of fetal liver were significantly decreased in the exercise group (p < 0.01 and p < 0.05, respectively). These results indicate that maternal exercise significantly increases plasma levels of GH, IGF-I and IGFBP-3 in the late period of pregnancy but causes adverse effects on fetal growth.

Correlations of growth hormone (GH) and insulin-like growth factor I (IGF-I): effects of exercise and abuse by athletes

The importance of hormones on body metabolism when physical exercise is carried out has been established for a long time. Growth hormone (GH) is crucial in energy metabolism as well as in body anabolism. Recent studies have increased our knowledge of GH's mechanisms of action. In particular, insulin-like growth factor I (IGF-I), the main hormone mediating the principal GH effects and other protein structures (i.e. the binding proteins related to these two hormones), has been recognized as playing a crucial role. The biochemical aspects relating to the molecules of the GH/IGF-I axis have been described here. Furthermore, the belief that GH and IGF-I enhance performance has induced an 'abuse' of GH (and possibly of IGF-I) by competitive sports athletes and amateurs. The present study outlines the best methods available to uncover abuse, as well as a series of potential research projects to recognize doping. The review also underlines the principal variables measurable in the laboratory and summarizes published reference ranges of these parameters. These biochemical and laboratory profiles describe principal experimental approaches, with the hope that this will stimulate new ideas on the subject of detecting doping practices.

Role of submaximal exercise in promoting creatine and glycogen accumulation in human skeletal muscle

We examined the effect of glycogen-depleting exercise on subsequent muscle total creatine (TCr) accumulation and glycogen resynthesis during postexercise periods when the diet was supplemented with carbohydrate (CHO) or creatine (Cr) + CHO. Fourteen subjects performed one-legged cycling exercise to exhaustion. Muscle biopsies were taken from the exhausted (Ex) and nonexhausted (Nex) limbs after exercise and after 6 h and 5 days of recovery, during which CHO (CHO group, n = 7) or Cr + CHO (Cr+CHO group, n = 7) supplements were ingested. Muscle TCr concentration ([TCr]) was unchanged in both groups 6 h after supplementation commenced but had increased in the Ex (P < 0.001) and Nex limbs (P < 0.05) of the Cr+CHO group after 5 days. Greater TCr accumulation was achieved in the Ex limbs (P < 0.01) of this group. Glycogen was increased above nonexercised concentrations in the Ex limbs of both groups after 5 days, with the concentration being greater in the Cr+CHO group (P = 0.06). Thus a single bout of exercise enhanced muscle Cr accumulation, and this effect was restricted to the exercised muscle. However, exercise also diminished CHO-mediated insulin release, which may have attenuated insulin-mediated muscle Cr accumulation. Ingesting Cr with CHO also augmented glycogen supercompensation in the exercised muscle.

Exercise-induced changes in protein metabolism

Exercise has a profound acute effect on protein metabolism. Whereas reports on whole body responses to exercise have varied results, it is generally agreed leucine oxidation is increased during exercise, thus indicating increased net protein breakdown. Following endurance exercise, whole body protein breakdown is generally reduced from resting levels, while following eccentric exercise, both whole body protein breakdown and leucine oxidation are increased. Whole body protein synthesis, on the other hand, is either increased or unchanged. Much of the disagreement in the results of studies on the response of whole body protein metabolism to exercise may be attributed to the limitations of the available methods. Even if the methodology accurately reflects whole body metabolism, this may not reflect changes in the protein metabolism of muscle. Although endurance exercise has not been studied, muscle protein breakdown is increased following resistance exercise. There is a concomitant, and qualitatively greater, increase in muscle protein synthesis following resistance exercise, which may last for as long as 48 h. Increased muscle protein synthesis is linked to increased intramuscular availability of amino acids, and thus, to increased blood flow and increased amino acid delivery to the muscle, as well as increased amino acid transport. Administration of exogenous amino acids after exercise increases protein synthesis while ameliorating protein breakdown, thus improving net muscle protein balance. While it is clear that muscle protein synthesis and protein breakdown increase in a qualitatively similar manner following exercise, the mechanisms of stimulation have yet to be determined. However, we propose that the intracellular availability of amino acids is the link between these processes.

The response on glucoregulatory hormones of in vivo whole body hyperthermia

This study was designed to examine the effects of in vivo hyperthermia on the circulating concentrations of a number of glucoregulatory hormones potentially involved in immunomodulation. Eight healthy male volunteers were immersed for 2 h in a hot water bath (water temperature 39.5 degrees C) (WI) during which period their rectal temperature rose to 39.5 degrees C. In a control study the subjects were immersed in thermoneutral water (water temperature 34.5 degrees C). Blood samples were collected before, at body temperature 38 degrees C (42.5 (30-52), median and range), minutes of hot WI, 39 degrees C (72.5 (58-97) minutes of hot WI), and 39.5 degrees C (at the end of 2 h of hot WI), as well as 1 and 2 h after cessation of 2 h of hot WI. In the control experiment blood samples were collected at identical time points. The growth hormone concentrations were elevated already at 38 degrees C to 24.2 (3.9-55.0) mU/l and peaked at 39 degrees C to 48.4 (20.8-81.5) mU/l compared to 0.3 (0.3-9.0) mU/l at baseline; at 39.5 degrees C the concentration declined to 31.6 (13.0-48.0) mU/l and further to 7.4 (0.8-17.3) mU/l 1 h after ending hot WI. The beta-endorphin levels were augmented at 39 degrees C and 39.5 degrees, to 8.0 (3.4-27.8) pmol/l and 8.1 (3.1-44.6) pmol/l, respectively, from 2.2 (0.7-5.6) pmol/l baseline. Glucagon levels raised from 23.0 (12.0-32.0) pmol/l to 32.0 (24.0-52.0) pmol/l at 39 degrees C, and to 38.5 (26.0-57.0) pmol/l at 39.0 degrees C. Insulin levels remained unchanged. Plasma glucose increased from 4.75 (4.2-7.6) mmol/l to 5.20 (4.6-5.6) mmol/l alone after 90 min of WI (temperature 39-39.5 degrees C). It is concluded that in vivo whole body WI hyperthermia increases the circulating levels of several essential glucoregulatory hormones.

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.

Effect of the enhancement of the cholinergic tone by pyridostigmine on the exercise-induced growth hormone release in man

We have evaluated the effect of pyridostigmine (PD), a cholinergic agonist, on the growth hormone (GH) response to physical exercise (EXC) in nine healthy volunteers. PD administration and EXC caused a similar increase of GH secretion to mean (+/- SE) peak values of 5.3 +/- 0.9 and 6.5 +/- 1.2 micrograms/l, respectively. Pretreatment with PD caused a significant augmentation of the EXC-induced GH release evaluated both as maximum peak (13.5 +/- 2.1 micrograms/l, p < 0.01 vs EXC) and as area under the secretory curve (EXC = 292.6 +/- 41.9 micrograms.min.l; PD + EXC = 587.3 +/- 68.9 micrograms.min.l, p < 0.005). The action of PD on GH secretion was additive to that of EXC since the sum of the GH responses to PD and EXC was not significantly different from the response obtained during PD + EXC. Whether PD and EXC act through a common final pathway, i.e. inhibition of endogenous somatostatin release, or the EXC-induced GH secretion involves stimulation of endogenous GHRH remains matter of investigation.

Voluntary exercise and experimental mammary cancer

The results of these studies indicate that voluntary activity suppresses the development of chemically and virally induced primary mammary tumors in rats and mice fed high-fat diets. These diets were chosen to mimic the current U.S. fat consumption of approximately 40% of calories as fat. It remains to be seen if activity exerts a similar suppressive effect on animals fed their customary low-fat diet (10% calories as fat). In general, the activity profiles of the female Fischer F-344 and Sprague-Dawley rat and the C3H/o mu j mouse exhibited a similar pattern with an early peak followed by a gradual plateau over time. The effects of activity on body fat composition showed a trend toward a decreased percent of body fat when compared to sedentary animals but a statistically significant decrease was found only in the F-344 female rat. In the DMBA model, carcinogen dose did alter outcome parameters. For example, time to first tumor was extended under low- but not high-DMBA conditions, and, conversely, tumor multiplicity was significantly decreased in the high- but not low-DMBA group. In the NMU model, an inverse association was found between the amount of activity and tumor incidence. A similar association was not found with the DMBA model. The reason for this is uncertain, but further analysis in terms of other parameters such as total tumor number may shed more light on this discrepancy. The suppressive effect of activity on the MMTV-induced mouse mammary tumor is of particular interest since it raises the possibility that activity may exert effects on the process of provirus insertion, and/or oncogene activation--an area of great potential promise in cancer prevention. Activity appeared to enhance the volume and to a lesser degree the number of metastatic foci in the lungs of F-344 retired breeders under high-fat but not medium-fat conditions. In addition, the most active animals in the high-fat group exhibited the greatest volume of metastases. These results, together with those in the NMU model, point to the critical importance of the quantity of voluntary activity an animal engages in and its relation to both primary and secondary cancer prevention. They imply that beyond a certain point of either frequency or intensity, the beneficial effect of exercise may be nullified by competing deleterious effects. The metastases study has also brought to light the importance of dietary fat as a potential intervening variable.(ABSTRACT TRUNCATED AT 400 WORDS)

Plasma levels of beta-endorphin, prolactin and gonadotropins in male athletes after an international nordic ski race

Plasma beta-endorphin, prolactin (PRL), FSH and LH were measured in 17 volunteer male subjects at rest and under the stress caused by a long-distance nordic ski race. The race induced increased levels of beta-endorphin and PRL in all skiers. The changes in PRL with exercise were significantly related to the changes in beta-endorphin (r = 0.69, p less than 0.001). Furthermore, the highly trained skiers training over 150 km.week-1 of nordic ski showed consistently higher post-exercise beta-endorphin and PRL levels than the moderately trained skiers who trained for 20 km.week-1. In addition the race induced slight falls in FSH and LH; however plasma gonadotropin levels did not show any correlation with plasma beta-endorphin concentrations and did not differ between the two groups of skiers. These results suggest that endogenous opioid peptides may modulate PRL secretion in heavy exercise, since they are of minor importance in the release of FSH and LH in such a situation. The observations also suggest that the degree of previous training and the exercise intensity do seem to be responsible for the hormonal changes.