Effect of marathon run on serum IGF-I and IGF-binding protein 1 and 3 levels

Exercise to spot the differences: a framework for the effect of exercise on hippocampal pattern separation in humans

Exercise has a beneficial effect on mental health and cognitive functioning, but the exact underlying mechanisms remain largely unknown. In this review, we focus on the effect of exercise on hippocampal pattern separation, which is a key component of episodic memory. Research has associated exercise with improvements in pattern separation. We propose an integrated framework mechanistically explaining this relationship. The framework is divided into three pathways, describing the pro-neuroplastic, anti-inflammatory and hormonal effects of exercise. The pathways are heavily intertwined and may result in functional and structural changes in the hippocampus. These changes can ultimately affect pattern separation through direct and indirect connections. The proposed framework might guide future research on the effect of exercise on pattern separation in the hippocampus.

The effect of 30-m repeated sprint exercise on muscle damage indicators, serum insulin-like growth factor-Iand cortisol

Study aim: The purpose of this study was to examine the effects of arepeated sprint exercise protocol on muscle damage indicators, serum IGF-Iand cortisol levels.

Material and methods: Nine trained male subjects (age 23.3 ± 3.6 years) completed arepeated sprint protocol consisting of two sets of 10 × 30-m maximal sprints with 30 s of active recovery between sprints and 5 min of passive recovery between sets. The isometric strength and flexibility were measured before, immediately after and 24 hours after exercise. 30-m maximal sprint time was measured before and 24 hours after exercise. Blood samples were taken before, immediately after and 24 hours after exercise.

Results: Isometric strength and flexibility were significantly decreased after exercise and 24 hours after exercise (p < 0.05). 30-m sprint time was significantly increased 24 hours after exercise (p < 0.05). Asignificant increase in serum lactate dehydrogenase, IGF-Iand cortisol were found after exercise (p < 0.05). Serum creatine kinase increased significantly immediately after and 24 hours after exercise compared to pre-exercise values (p < 0.05).

Conclusion: Our data show that due to increased serum IGF-Ilevel, repeated sprint exercise may have anabolic effects as well as traumatic effects on the muscles.

Insulin-like growth factor I, binding proteins -1 and -3, risk of type 2 diabetes and macronutrient intakes in men

The insulin-like growth factor (IGF) axis may be involved in the development of type 2 diabetes. We examined the associations of IGF-I and IGF binding proteins (IGFBP)-1 and -3 with diabetes risk and evaluated macronutrient intakes related to the observed associations. In a nested case-control study of the Alpha-Tocopherol, Beta-Carotene Cancer Prevention Study of Finnish male smokers aged 50-69 years, the IGF variables were measured from baseline serum samples for a random sample of 310 men with diabetes diagnosed during a 12-year follow-up and for 310 controls matched by age, recruitment day and intervention group. Diet at baseline was assessed using a validated FFQ. The associations of IGF proteins with diabetes risk were estimated using conditional logistic regression and the associations with macronutrient intakes using linear regression. IGF-I and IGFBP-3 were not associated with the incidence of diabetes. Higher IGFBP-1 was associated with lower diabetes risk in an unadjusted crude model (OR 0·25; 95 % CI 0·15, 0·42 in the highest quartile compared with the lowest), but not after adjustment for BMI (corresponding OR 0·76; 95 % CI 0·41, 1·40). Intakes of carbohydrates, plant protein and milk protein associated positively and intake of meat protein and fat negatively with IGFBP-1 (P&lt;0·005). IGFBP-1 was inversely associated with diabetes risk, but the association was substantially dependent on BMI. The associations between macronutrient intakes and IGFBP-1 may reflect influences of nutrients or foods on insulin concentrations.

Exercise-Induced Neuroplasticity: A Mechanistic Model and Prospects for Promoting Plasticity

Aerobic exercise improves cognitive and motor function by inducing neural changes detected using molecular, cellular, and systems level neuroscience techniques. This review unifies the knowledge gained across various neuroscience techniques to provide a comprehensive profile of the neural mechanisms that mediate exercise-induced neuroplasticity. Using a model of exercise-induced neuroplasticity, this review emphasizes the sequence of neural events that accompany exercise, and ultimately promote changes in human performance. This is achieved by differentiating between neuroplasticity induced by acute versus chronic aerobic exercise. Furthermore, this review emphasizes experimental considerations that influence the opportunity to observe exercise-induced neuroplasticity in humans. These include modifiable factors associated with the exercise intervention and nonmodifiable factors such as biological sex, ovarian hormones, genetic variations, and fitness level. To maximize the beneficial effects of exercise in health, disease, and following injury, future research should continue to explore the mechanisms that mediate exercise-induced neuroplasticity. This review identifies some fundamental gaps in knowledge that may serve to guide future research in this area.

Preparatory training attenuates drastic response of the insulin-like growth factor binding protein 1 at the point of maximal oxygen consumption in handball players

BACKGROUND

Intensive exercise changes physiological need for glucose and several biochemical pathways responsible for its metabolism response. Among them are those which involve insulin, insulin-like growth factor (IGF-1), and IGF-binding proteins (IGFBPs). Different types and degrees of exercise, as well as an athlete's fitness, may induce a range of responses regarding concentrations and time needed for the alteration. The idea of the work was to find out whether and how insulin/IGF axis responds to additional physical activity in the already trained subjects and if so, is the adaptation potentially beneficial from the aspect of metabolic control.

METHODS

The effect of 4-week intensive training on campus (preparatory training) on the levels of insulin, IGF-1, and IGFBPs during maximal progressive exercise test (MPET) on a treadmill was compared to the results obtained during MPET conducted after a regular training season of a female elite handball team (n = 17, age: 17 ± 1 years, height: 171 ± 8 cm, weight: 65 ± 8 kg, body mass index: 22 ± 1 kg/m2 at the beginning of the study; there were no significant changes at the end). Serum samples were obtained from players immediately before the test (basal), at the end of the test after reaching the point of maximal oxygen consumption (VO2max), and after recovery.

RESULTS

The concentration of insulin decreased at VO2max, but remained higher in players after preparatory training (12.2 ± 2.5 mU/L vs. 8.9 ± 4.4 mU/L, p = 0.049). The level of IGFBP-1 decreased in players at VO2max in either case of training, but it remained much higher in tests performed after the preparatory regime than before (p = 0.029). Concentrations of IGF-1, IGFBP-2, -3, and -4 did not change significantly.

CONCLUSION

The inverse relation between insulin and IGFBP-1 was lost during MPET, as these 2 molecules changed in the same direction. The results obtained suggest less severe stress-induced depression of insulin and IGFBP-1 after preparatory training. But another metabolic mechanism cannot be excluded, and that is potentially impaired insulin sensitivity resulting in higher level of IGFBP-1.

Changes in cytokines, leptin, and IGF-1 levels in overtrained athletes during a prolonged recovery phase: A case-control study

We investigated how cytokines are implicated with overtraining syndrome (OTS) in athletes during a prolonged period of recovery. Plasma IL-6, IL-10, TNF-α, IL-1β, adipokine leptin, and insulin like growth factor-1 (IGF-1) concentrations were measured in overtrained (OA: 5 men, 2 women) and healthy control athletes (CA: 5 men, 5 women) before and after exercise to volitional exhaustion. Measurements were conducted at baseline and after 6 and 12 months. Inflammatory cytokines did not differ between groups at rest. However, resting leptin concentration was lower in OA than CA at every measurement (P < 0.050) but was not affected by acute exercise. Although IL-6 and TNF-α concentrations increased with exercise in both groups (P < 0.050), pro-inflammatory IL-1β concentration increased only in OA (P < 0.050) and anti-inflammatory IL-10 was greater in CA (P < 0.001). In OA, exercise-related IL-6 and TNF-α induction was enhanced during the follow-up (P < 0.050). IGF-1 decreased with exercise in OA (P < 0.050); however, no differences in resting IGF-1 were observed. In conclusion, low leptin level at rest and a pro-inflammatory cytokine response to acute exercise may reflect a chronic maladaptation state in overtrained athletes. In contrast, the accentuation of IL-6 and TNF-α responses to acute exercise seemed to associate with the progression of recovery from overtraining.

Rigorous Running Increases Growth Hormone and Insulin-Like Growth Factor-I Without Altering Ghrelin

It has been suggested that ghrelin may play a role in growth hormone (GH) responses to exercise. The present study was designed to determine whether ghrelin, GH, insulin-like growth factor-I (IGF-I), and IGF-binding protein-3 (IGFBP-3) were altered by a progressively intense running protocol. Six well-trained male volunteers completed a progressively intense intermittent exercise trial on a treadmill that included four exercise intensities: 60%, 75%, 90%, and 100% of Vo2max. Blood samples were collected before exercise, after each exercise intensity, and at 15 and 30 mins following the exercise protocol. Subjects also completed a separate control trial at the same time of day that excluded exercise. GH changed significantly over time, and GH area under the curve (AUC) was significantly higher in the exercise trial than the control trial. Area under the curve IGF-I levels for the exercise trial were significantly higher than the control trial. There was no difference in the ghrelin and IGFBP-3 responses to the exercise and control trials. Pearson correlation coefficients revealed significant relationships between ghrelin and both IGF-I and IGFBP-3; however, no relationship between ghrelin and GH was found. In conclusion, intense running produces increases in total IGF-I concentrations, which differs from findings in previous studies using less rigorous running protocols and less frequent blood sampling regimens. Moreover, running exercise that produces substantial increases in GH does not affect peripheral ghrelin levels; however, significant relationships between ghrelin and both IGF-I and IGFBP-3 exist during intense intermittent running and recovery, which warrants further investigation.

Insulin-Like Growth Factor-1 and Selected Insulin-Like Growth Factor Binding Protein Concentrations during an Ultramarathon Sled Dog Race

The objective of this study was to investigate the effects of running a 1000-mile (1600 km) endurance sled dog race on serum insulin-like growth factor-1 (IGF-1) and insulin-like growth factor binding proteins 1 and 3 (IGFBP-1 and IGFBP-3). Serum was examined from 12 sled dogs prior to the race, at midrace (approximately 690 km), and again at the finish. IGF-1, IGFBP-1, and IGFBP-3 were assessed using radioimmunoassay or enzyme linked immune-absorbance assays. Mean prerace concentrations were significantly higher than midrace and end-race concentrations at 215.93 ± 80.51 ng/mL, 54.29 ± 25.45 ng/mL, and 55.53 ± 28.25 ng/mL, respectively (P < 0.001). Mean IGFBP-1 concentrations were not different across these time periods at 24.1 ± 15.8 ng/mL, 25.7 ± 14.0 ng/mL, and 26.6 ± 17.6 ng/mL, respectively. IGFBP-3 concentrations showed a modest significant decrease across time periods at 3,067 ± 2,792 ng/mL, 2,626 ± 2,310 ng/mL, and 2,331 ± 2,301 ng/mL, respectively (P < 0.01). Endurance sled dogs show a precipitous drop in serum IGF-1 concentrations. These differences may be related to fuel utilization and excessive negative energy balance associated with the loss of body condition during racing. The relative stability of IGFBP-1 and IGFBP-3 suggests that IGF-1 anabolic signaling is diminished during ultramarathon racing. Further studies comparing the influence of time and duration of exercise versus negative energy balance on serum IGF-1 status are warranted to better understand exercise versus negative energy balance differences.

Vitamin D supplementation affects the IGF system in men after acute exercise

OBJECTIVE

Contradictory data between the Insulin-Like Growth Factor System (IGF) system and exercise may be due to alteration in IGF binding proteins. Vitamin D (D) deficiency has been related to muscle weakness and Insulin Like Growth Factor Binding Protein 3 (IGFBP3). A Vit. D and acute exercise merge is proposed to modify the IGF system.

DESIGN

D insufficient and deficient men (39.0±8.6yo with serum D (25OH D) 20.0±7.7ng/mL) did 1h of stretching (ST), aerobic (AB), and resistance (RT) exercises, before and after 28d of 4000IU/d Vit. D3 (D, n=6) or Placebo (P, n=7). ST, a time/attention control visit, interchanged unreceptive movements. AB was moderate intensity treadmill walking. RT rotated moderate strength 50% 1-RM repetitions (15, 10) of squat, bench press, leg press, and lat pull down. Serum Total IGF1 (TIGF1), Insulin Like Growth Factor Binding Protein 1 (IGFBP1), and IGFBP3 were measured before (T1, fasting), immediately after (T2), and 2h post (T3) exercise.

RESULTS

After ST, IGFBP3 was greater in the D group at T2 (2948, 2130ng/mL; p<0.03) and T3 (3087, 2212; p<0.02). During RT, TIGF1 decreased in the Placebo (P) group from T1 to T3 (151.4, 107.3ng/mL; p<0.05), while IGFBP1 increased in the D group from T1 to T3 (26.5, 96.2ng/mL; p<0.05). RT IGFBP3 was greater at T1, T2, and T3 in the D group (2932.5, 2110.7; p<0.03), (3163.9, 2392.5; p<0.04), and (3355.3, 2353.1; p<0.01). In AB, IGFBP3 was greater in the D group at T2 (3128.6, 2226.3.0; p<0.04) and T3 (2949.7, 2135.1; p<0.05).

CONCLUSION

D supplementation amplified IGFBP3 after low or moderate activity which may increase the delivery of IGF1 to tissues. Resistance exercise with D not only increased IGFBP3 and IGFBP1 levels but also conserved TIGF1 levels, possibly shifting the IGF system for enriched muscle well-being.

The change in thyroid hormone signaling by altered training intensity in male rat skeletal muscle

Aerobic (sub lactate threshold; sub-LT) exercise training facilitates oxidative phosphorylation and glycolysis of skeletal muscle. Thyroid hormone (TH) also facilitates such metabolic events. Thus, we studied whether TH signaling pathway is activated by treadmill training. Male adult rats received 30 min/day treadmill training with different exercise intensity for 12 days. Then plasma lactate and thyrotropin (TSH) levels were measured. By lactate levels, rats were divided into stationary control (SC, 0 m/min), sub-LT (15 m/min) and supra lactate threshold (supra-LT; 25 m/min) training groups. Immediately after the last training, the soleus muscles were dissected out to measure TH receptor (TR) mRNA and protein expressions. Other rats received intraperitoneal injection of T3, 24 h after the last training and sacrificed 6 h after the injection to measure TH target gene expression. TSH level was suppressed in both sub-LT and supra-LT groups during the exercise. TRβ1 mRNA and protein levels were increased in sub-LT group. Sensitivity to T3 was altered in several TH-target genes by training. Particularly, induction of Na(+)/K(+)-ATPase β1 expression by T3 was significantly augmented in sub-LT group. These results indicate that sub-LT training alters TH signaling at least in part by increasing TRβ1 expression. Such TH signaling alteration may contribute metabolic adaptation in skeletal muscle during physical training.

Serum zinc and risk of type 2 diabetes incidence in men: The Kuopio Ischaemic Heart Disease Risk Factor Study

OBJECTIVES

Zinc may play a role in the development of type 2 diabetes (T2D), because it is involved in antioxidant and anti-inflammatory activities. However, the role of zinc in the etiology of T2D has been poorly investigated. This study was conducted to study the association of serum zinc on T2D risk in middle-aged and older Finnish men.

METHODS

This was a 20-year prospective follow-up study on 2220 Finnish men from the Kuopio Ischaemic Heart Disease Risk Factor Study (KIHD) who were 42 to 60 years old at baseline in 1984-1989. The main outcome was incident T2D. Serum zinc, body mass index (BMI), fasting blood glucose (FBG), serum insulin, C-reactive protein (CRP) and, in a subset of 751 participants, insulin-like growth factor-binding protein-1 (IGFBP-1), were measured. Also, the homeostatic model assessment (HOMA) was used to quantify insulin resistance (HOMA-IR), beta-cell function (HOMA-β) and insulin sensitivity (HOMA-IS).

RESULTS

At baseline, serum zinc was associated with higher BMI, serum insulin, HOMA-IR, HOMA-β and IGFBP-1 and lower HOMA-IS. During the average follow-up of 19.3 years, 416 men developed T2D. Men in the highest quartile of serum zinc had 60% higher risk (95% CI 20-113%; P-trend<0.001) for incident T2D compared with the men in the lowest quartile, after multivariate adjustments. This association was attenuated after adjustment for BMI (HR=1.39, 95% CI 1.04-1.85; P-trend=0.013) or HOMA-IS (HR=1.38, 95% CI 1.04-1.83; P-trend=0.015), whereas adjustment for the other factors had only modest impact on the association.

CONCLUSION

Higher serum zinc was associated with higher risk of T2D; effects of zinc on BMI and insulin sensitivity may partly explain the association. Further prospective studies are warranted to confirm our results and explore potential mechanisms.

Concurrent aerobic exercise interferes with the satellite cell response to acute resistance exercise

The addition of aerobic exercise (AE) to a resistance exercise (RE) program (concurrent exercise, CE) can interfere with maximum muscle fiber growth achieved with RE. Further, CE appears to markedly affect the growth of myosin heavy chain (MHC) I, but not MHC IIa fibers. The mechanism responsible for this “interference” is unclear. Satellite cell (SC) responsiveness to exercise appears to influence muscle adaptation but has not yet been examined following acute concurrent exercise. Thus, we assessed the fiber-type-specific SC response to RE, AE, and CE exercise. Eight college-aged males completed the following two exercise trials: the RE trial, which consisted of unilateral leg extensions and presses (4 sets ≥ 10 repetitions: 75% 1 repetition maximum, RM); and the AE/CE trial, which included an identical RE protocol with the opposite leg, immediately followed by subjects cycling for 90 min (60% Wmax). Muscle biopsies were obtained from the vastus lateralis before and 4 days after each session. Samples were cross-sectioned, stained with antibodies against NCAM, Ki-67, and MHC I, counterstained with DAPI, and analyzed for SC density (SC per fiber), SC activation, and fiber type. SC density increased to a greater extent following RE (38 ± 10%), compared with CE (−6 ± 8%). Similarly, MHC I muscle fiber SC density displayed a greater increase following RE (46 ± 14%), compared with AE (−7 ± 17%) and CE (−8 ± 8%). Our data indicate that the SC response to RE is blunted when immediately followed by AE, at least in MHC I muscle fibers, and possibly MHC II fibers. This suggests that the physiological environment evoked by AE might attenuate the eventual addition of myonuclei important for maximum muscle fiber growth and consequent force-producing capacity.

Aerobic exercise training increases circulating insulin-like growth factor binding protein-1 concentration, but does not attenuate the reduction in circulating insulin-like growth factor binding protein-1 after a high-fat meal

Insulin-like growth factor binding protein-1 (IGFBP-1) has metabolic effects throughout the body, and its expression is regulated in part by insulin. Circulating IGFBP-1 predicts development of cardiometabolic diseases in longitudinal studies, and low IGFBP-1 concentrations are associated with insulin resistance and consumption of a high-fat diet. Because of the favorable metabolic effects of regular aerobic exercise, we hypothesized that aerobic exercise training would increase plasma IGFBP-1 concentrations and attenuate the reduction in IGFBP-1 after a high-fat meal. Ten overweight (body mass index = 28.7 ± 0.9 kg/m(2)), older (61 ± 2 years) men and women underwent high-fat feeding and oral glucose tolerance tests at baseline and after 6 months of aerobic exercise training. In response to aerobic exercise training, subjects increased cardiorespiratory fitness by 13% (P < .05) and insulin sensitivity index by 28% (P < .05). Basal plasma concentrations of IGFBP-1 increased by 41% after aerobic exercise training (P < .05). The insulin response to an oral glucose tolerance test was a significant predictor of fasting plasma IGFBP-1 concentrations at baseline and after exercise training (P = .02). In response to the high-fat meal at baseline, plasma IGFBP-1 concentrations decreased by 58% (P < .001); a 61% decrease to similar postprandial concentrations was observed after exercise training (P < .001). Plasma insulin response to the high-fat meal was inversely associated with postprandial IGFBP-1 concentrations at baseline and after exercise training (P = .06 and P < .05, respectively). Although aerobic exercise training did not attenuate the response to a high-fat meal, the increase in IGFBP-1 concentrations after exercise training may be one mechanism by which exercise reduces risk for cardiometabolic diseases in older adults.

Biochemical markers of bone turnover in tibia fracture patients randomly assigned to growth hormone (GH) or placebo injections: Implications for detection of GH abuse

CONTEXT

It has been argued that increased levels of bone remodelling markers are not suitable indicators of GH abuse, as bone injuries per se increase the expression levels of these markers.

OBJECTIVE

To investigate the impact of a recovering tibia fracture on circulating bone markers in subjects receiving placebo or GH treatment.

DESIGN AND SETTING

A randomised, double-blind, placebo-controlled trial of up to 16weeks GH treatment, followed by a 16-week washout.

PARTICIPANTS AND INTERVENTION

Subjects (406 adult males and females) with a tibia fracture were randomly allocated within three days after surgery, to either placebo or GH treatment (15, 30 or 60μg/kg daily) until fracture healing or 16weeks after treatment initiation.

MAIN OUTCOME MEASURES

IGF-I, serum C-terminal telopeptide of type I collagen (CTX), osteocalcin (OST) and bone-specific alkaline phosphatase (BAP) were measured during and after treatment.

RESULTS

Dose-dependent increases were observed in groups receiving GH, and mean levels in the highest GH dose group peaked at eight (IGF-I, CTX) or 12weeks (OST) after treatment initiation. Statistically significant differences between GH treatment and placebo were seen for IGF-I, CTX and OST in all GH dose groups throughout the treatment period, and persisted until eight (CTX) or 12 (OST) weeks after cessation of treatment.

CONCLUSION

IGF-I, CTX and OST are suitable candidate markers of prolonged, illicit administration of GH. Furthermore, CTX and OST have potentials to serve as markers also after cessation of GH administration.

Ingestion of 10 grams of whey protein prior to a single bout of resistance exercise does not augment Akt/mTOR pathway signaling compared to carbohydrate

Background

This study examined the effects of a whey protein supplement in conjunction with an acute bout of lower body resistance exercise, in recreationally-active males, on serum insulin and insulin like growth factor 1 (IGF-1) and Akt/mTOR signaling markers indicative of muscle protein synthesis: insulin receptor substrate 1 (IRS-1), AKT, mammalian target of rapamycin (mTOR), p70S6 kinase (p70S6K) and 4E-binding protein 1 (4E-BP1).

Methods

In a randomized, double-blind, cross-over design, 10 males ingested 1 week apart, either 10 g of whey protein (5.25 g EAAs) or carbohydrate (maltodextrose), 30 min prior to a lower-body resistance exercise bout. The resistance exercise bout consisted of 4 sets of 8-10 reps at 80% of the one repetition maximum (RM) on the angled leg press and knee extension exercises. Blood and muscle samples were obtained prior to, and 30 min following supplement ingestion and 15 min and 120 min post-exercise. Serum and muscle data were analyzed using two-way ANOVA.

Results

No significant differences were observed for IGF-1 (p > 0.05). A significant main effect for Test was observed for serum insulin (p < 0.01) at 30 min post-ingestion and 15 and 120 min post-exercise, with no Supplement × Test interaction (p > 0.05). For the Akt/MTOR signaling intermediates, no significant Supplement × Test interactions were observed (p > 0.05). However, significant main effects for Test were observed for phosphorylated concentrations of IRS, mTOR, and p70S6K, as all were elevated at 15 min post-exercise (p < 0.05). Additionally, a significant main effect for Test was noted for 4E-BP1 (p < 0.05), as it was decreased at 15 min post-exercise.

Conclusion

Ingestion of 10 g of whey protein prior to an acute bout of lower body resistance exercise had no significant preferential effect compared to carbohydrate on systemic and cellular signaling markers indicative of muscle protein synthesis in untrained individuals.

Aerobic exercise improves hippocampal function and increases BDNF in the serum of young adult males

Physical activity has been reported to improve cognitive function in humans and rodents, possibly via a brain-derived neurotrophic factor (BDNF)-regulated mechanism. In this study of human subjects, we have assessed the effects of acute and chronic exercise on performance of a face-name matching task, which recruits the hippocampus and associated structures of the medial temporal lobe, and the Stroop word-colour task, which does not, and have assessed circulating concentrations of BDNF and IGF-1 in parallel. The results show that a short period of high-intensity cycling results in enhancements in performance of the face-name matching, but not the Stroop, task. These changes in cognitive function were paralleled by increased concentration of BDNF, but not IGF-1, in the serum of exercising subjects. 3 weeks of cycling training had no effect on cardiovascular fitness, as assessed by VO2 scores, cognitive function, or serum BDNF concentration. Increases in fitness, cognitive function and serum BDNF response to acute exercise were observed following 5 weeks of aerobic training. These data indicate that both acute and chronic exercise improve medial temporal lobe function concomitant with increased concentrations of BDNF in the serum, suggesting a possible functional role for this neurotrophic factor in exercise-induced cognitive enhancement in humans.

Functional overreaching during preparation training of elite tennis professionals

This case study evaluated the response of objective and subjective markers of overreaching to a highly demanding conditioning training mesocycle in elite tennis players to determine 1) whether players would become functionally or non-functionally overreached, and 2) to explore how coherently overreaching markers would respond. Performance, laboratory and cardiac autonomous activity markers were evaluated in three experienced male tennis professionals competing at top 30, top 100 and top 1000 level before and after their strength and conditioning training was increased by 120, 160 and 180%, respectively, for 30 days. Every week, subjective ratings of stress and recovery were evaluated by means of a questionnaire. After 74, 76 and 55 h of training, increases in V̇O2max (+8, +5 and +18%) and speed strength indices (+9, +23 and +5%) were observed in all players. Changes of maximal heart rate (-5, -6, +4 beats per minute), laboratory markers (e.g. insulin-like growth factor -26, -17, -9%; free testosterone to cortisol ratio -63, +2, -12%) and cardiac autonomous activity markers (heart rate variability -49, -64, -13%) were variable among the players. Improved performance provides evidence that overreaching was functional in all players. However, several overreaching markers were altered and these alterations were more pronounced in the two top 100 players. The response of overreaching indicators was not coherent.

Effect of high- and low-intensity exercise and metabolic acidosis on levels of GH, IGF-I, IGFBP-3 and cortisol

OBJECTIVE

The purpose of the present study was to examine the acute hormonal response of a short term high-intensity training (HIT) versus a high volume endurance training (HVT) and to determine the contribution of the metabolic acidosis as a stimulus for possibly different reactions of circulating hGH, IGF-1, IGFBP-3 and cortisol.

DESIGN

Eleven subjects participated in three experimental trials separated by one week. Two times subjects performed four 30s maximal effort exercise bouts on a cycle ergometer separated by 5 min rest each. Before the exercise subjects either received (single-blinded) bicarbonate (HIT (B)) or a placebo (HIT (P)). The third exercise trail consisted of a constant load exercise for 1h at 50% VO₂max (HVT). Venous blood samples were taken under resting conditions, 10 min, 60 min and 240 min after each exercise condition to determine hGH, IGF-1, IGFBP-3 and cortisol serum concentrations. Capillary blood samples were taken to determine lactate concentrations and blood gas parameters.

RESULTS

Power output, mean lactate concentrations and mean pH values were significantly higher during HIT (B) compared to HIT (P). Serum cortisol and hGH concentrations were significantly increased 10 min post exercise in both HIT interventions. IGFBP-3 was only significantly increased after HIT (P), whereas IGF-1 was not affected by any of the interventions. HVT showed no significant effects on cortisol, hGH, IGF-1 and IGFBP-3 levels. Additionally it was shown that the diminished acidosis during HIT (B) attenuates the cortisol and hGH response.

CONCLUSIONS

The present study suggests that HIT/acidosis is a stimulus for exercise-induced cortisol/hGH secretion, but not for IGF-1 and IGFBP-3 under these experimental conditions. These findings might be relevant for arrangements of interval training, due to the fact that active or passive recovery during rest periods influence the acid base status and may therefore influence the hormonal response.

Effect of low-intensity aerobic exercise on insulin-like growth factor-I and insulin-like growth factor-binding proteins in healthy men

Increased concentrations of circulating insulin-like growth factor-I (IGF-I) or IGF-I relative to IGF-binding proteins (IGFBPs) are associated with increased risk of developing several forms of cancer. Conversely, exercise is linked with reduced risk. This study aims to investigate the effect of a low-intensity exercise program on circulating levels of IGF-I, IGFBP-1, and IGFBP-3, in previously sedentary males. Fourteen healthy men participated in cycle ergometer training at lactate threshold intensity for 60 min/day, 5 days/week for 6 weeks. After aerobic training, insulin sensitivity improved by 20%, while fasting insulin levels decreased by 13%. Simultaneously, low-intensity aerobic training decreased the circulating levels of IGF-I by 9%, while IGFBP-1 levels increased by 16%. An interesting finding was that higher pretraining level of IGF-I was associated with greater decline in IGF-I with training. Insulin-sensitizing low-intensity aerobic exercise is thus considered to be an effective method for downregulating IGF-I and upregulating IGFBP-1 levels.

Brief, high intensity exercise alters serum ghrelin and growth hormone concentrations but not IGF-I, IGF-II or IGF-I bioactivity

Exercise stimulates growth hormone (GH) release, but there are conflicting reports regarding the acute effects of exercise on circulating ghrelin and insulin-like growth factor (IGF) concentrations. This investigation examined (1) the effect of a single sprint on circulating GH, ghrelin and IGF concentrations as well as a marker of IGF-I bioactivity, and (2) whether the number of muscle actions performed during a sprint influences these responses. Seven healthy men completed 3 trials in a random order. In two exercise trials they performed a single 30-s sprint on a cycle ergometer against a resistance equivalent to either 7% (FAST) or 9% (SLOW) of their body mass. In the other they rested in the laboratory (CON). Blood samples were taken pre-, immediately post-, 10 and 30 min post-exercise, and at equivalent times in the CON trial. Total ghrelin concentrations declined after the sprint and were significantly lower after 30 min of recovery than they were pre-exercise (pre-exercise vs. 30 min; FAST, 0.62 (0.19) vs. 0.49 (0.16) microg/L, P<0.001; SLOW, 0.59 (0.15) vs. 0.47 (0.13) microg/L, P<0.001). GH concentrations increased in both exercise trials and were greater in the FAST than the SLOW trial. Serum concentrations of total IGF-I, free IGF-I, total IGF-II, and IGF-I bioactivity did not change after sprinting. In conclusion, sprint exercise suppresses total ghrelin concentrations and stimulates GH release but does not alter IGF concentrations or bioactivity.

The physiology of growth hormone and sport

The growth hormone (GH)/ insulin-like growth factor-I (IGF-I) axis exerts short-and long-term metabolic effects that are potentially important during exercise. Exercise is a potent stimulus to GH release and there is some evidence that the acute increase in GH is important in regulating substrate metabolism post-exercise. Regular exercise also increases 24-hour GH secretion rates, which potentially contributes to the physiologic changes induced by training. The effects of GH replacement in GH-deficient adults provide a useful model with which to study the effects of the more long-term effects of the GH/ IGF-I axis. There is convincing evidence that GH replacement increases exercise capacity. Measures of exercise performance including maximal oxygen uptake (VO2max) and ventilatory threshold (VeT) are impaired in GH deficiency and improved by GH replacement, probably through some combination of increased oxygen delivery to exercising muscle, increased fatty acid availability with glycogen sparing, increased muscle strength, improved body composition and improved thermoregulation. Administration of supraphysiologic doses of GH to athletes increases fatty acid availability and reduces oxidative protein loss particularly during exercise, and increases lean body mass. It is not known whether these effects translate to improved athletic performance, although recombinant human GH is known to be widely abused in sport. The model of acromegaly provides evidence that long-term GH excess does not result in improved performance but it is possible that a "window" exists in which the protein anabolic effects of supraphysiologic GH might be advantageous.

The growth hormone/insulin-like growth factor-I axis in exercise and sport

The syndrome of adult GH deficiency and the effects of GH replacement therapy provide a useful model with which to study the effects of the GH/IGF-I axis on exercise physiology. Measures of exercise performance including maximal oxygen uptake and ventilatory threshold are impaired in adult GH deficiency and improved by GH replacement, probably through some combination of increased oxygen delivery to exercising muscle, increased fatty acid availability with glycogen sparing, increased muscle strength, improved body composition, and improved thermoregulation. In normal subjects, in addition to the long-term effects of GH/IGF-I status, there is evidence that the acute GH response to exercise is important in regulating substrate metabolism after exercise. Administration of supraphysiological doses of GH to athletes increases fatty acid availability and reduces oxidative protein loss, particularly during exercise, and increases lean body mass. Despite a lack of evidence that these metabolic effects translate to improved performance, GH abuse by athletes is widespread. Tests to detect GH abuse have been developed based on measurement in serum of 1) indirect markers of GH action, and 2) the relative proportions of the two major naturally occurring isoforms (20 and 22kDa) of GH. There is evidence that exercise performance and strength are improved by administration of GH and testosterone in combination to elderly subjects. The potential benefits of GH in these situations must be weighed against potential adverse effects.

Exercise-dependent IGF-I, IGFBPs, and type I collagen changes in human peritendinous connective tissue determined by microdialysis

Microdialysis studies indicate that mechanical loading of human tendon during exercise elevates type I collagen production in tendon. However, the possibility that the insertion of microdialysis fibers per se may increase the local collagen production due to trauma has not been explored. Insulin-like growth factor I (IGF-I) and its binding proteins (IGFBPs), which are known to stimulate collagen production in animal tendons, may regulate the translation of mechanical loading to collagen synthesis. Systemic and tissue levels of IGF-I, IGFBP, and type I collagen metabolism markers [procollagen I COOH-terminal propeptide (PICP) and COOH-terminal telopeptide of type I collagen] were measured by microdialysis in peritendinous tissue of the human Achilles tendon in an exercise group (performing a 36-km run, n = 6) and a control group (no intervention, n = 6). An increase in local PICP concentration was seen in both groups after 72 h and stayed elevated in the exercise group at 96 h (P < 0.05). IGFBP-1 in both serum and dialysate increased in the exercise group immediately after exercise (P < 0.05), whereas IGFBP-3 decreased systemically (P < 0.05). Elevation of local IGFBP-4 was observed in both the control and exercise groups after 48 h (P < 0.05). Total IGF-I did not change in locally or systemically in either group. Our results indicate an increased local production of PICP in human peritendinous tissue in response to prolonged mechanical loading with part of the increase due to trauma from the sampling technique. Care must therefore be emphasized to minimize the numbers of insertions with microdialysis. We demonstrated an elevation of IGFBP-1 both systemically and peritendinously in response to prolonged acute exercise. The local increased collagen synthesis was preceded by an elevation of local concentration of IGFBP-4, suggesting that IGFBP-4 may have a key role in the IGF-axis effect on the human collagen synthesis in vivo.

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.

Adaptation of the hypothalamic-pituitary hormones during intensive endurance training

OBJECTIVE

Physical activity leads to changes in the hypothalamic-pituitary hormonal system. However, acute and long-term adaptations have not yet been precisely characterized. In this study, the changes of the hormonal system as a result of marathon training and running a marathon were examined. In particular, we focused on adaptations of the hypothalamic-pituitary-adrenocortical (HPA) axis, regarding the activation or inactivation of cortisol to cortisone by the 11beta-hydroxysteroid-dehydrogenase system (11beta-HSD).

DESIGN

Patient measurements: 8 healthy women and 11 healthy men volunteered for this study. Blood samples, 24-h urine and a dexamethasone suppression test were analysed for metabolic and hormonal parameters at five different dates 12 weeks around a marathon.

RESULTS

Cortisol and ACTH values decreased significantly 2 days after the marathon, whereas the activity of the whole body 11beta-HSD-1 was up-regulated. An increased suppression of cortisol levels was observed in the dexamethasone suppression test after 6 weeks of reduced training levels. Ghrelin was elevated 2 days after the marathon. Only minor changes in the other hypothalamic-pituitary-hormonal axes could be observed. However, the free androgen index increased significantly after 6 weeks of reduced training.

CONCLUSIONS

The HPA system appeared to become chronically activated by continuous physical training and therefore less sensitive to the dexamethasone suppression test. The acute stress of the marathon led to a central exhaustion of the HPA system with a paracrine counteraction by the activation of the 11beta-HSD system. Changes in the other hypothalamic-pituitary hormonal axes were the result of long-term differences in training levels and were not altered by the marathon.

IGFBP-3, a sensitive marker of physical training and overtraining

OBJECTIVE

To investigate the response of the somatotrope axis (insulin-like growth factor-1 (IGF-1), insulin-like growth factor binding protein-3 (IGFBP-3)) to intense exercise in relation to tiredness.

METHODS

The study involved 11 rugby players who completed a questionnaire intended to evaluate fitness or, conversely, overtraining and who agreed to plasma samples being taken before and after an international rugby match.

RESULTS

The main finding of our study is that we observed strong negative correlations between IGF-1 (r = 0.652) and IGFBP-3 (r = 0.824) levels and the overtraining state estimated using the French Society of Sport Medicine questionnaire. In particular, there was a fall (of up to 25%) in IGFBP-3 levels after the match in the more fatigued subjects compared to an increase (of up to 40%) in fit subjects.

CONCLUSIONS

A fall in IGFBP-3 in response to an intense bout of exercise may represent an index of tiredness in highly trained sportsmen, as indicated by the scores obtained from the overtraining questionnaire.

Cord serum insulin-like growth factor binding protein-1 and -3: effect of maternal diabetes and relationships to fetal growth

OBJECTIVES

Insulin-like growth factor binding protein-1 and -3 (IGFBP-1 and -3) are the main insulin-like growth factor (IGF) carriers in fetal blood whose concentrations are regulated by hormonal factors such as insulin. IGFBPs may regulate fetal growth by altering the biological activity of IGF-I and IGF-II. We studied the effect of maternal diabetes on cord serum IGFBP-1 and IGFBP-3 levels, and the usability of IGFBP-1 and IGFBP-3 in the detection of birth weight variations.

METHODS

Cord serum IGFBP-1 and IGFBP-3 concentrations were measured at birth by immunofluorometric assays in 67 pregnancies with type 1 diabetes and in 62 normal pregnancies.

RESULTS

Concentrations of IGFBP-1 in cord serum were lower in diabetic pregnancies than in normal pregnancies (156 +/- 28 microg/l vs 266 +/- 29 microg/l, P = 0.007), whereas those of IGFBP-3 did not differ significantly (3327 +/- 158 microg/l vs 2982 +/- 105 microg/l, P = 0.076). IGFBP-1 correlated negatively and IGFBP-3 positively with birth weight z-score in diabetic pregnancies. The trend was similar in normal pregnancies. In multiple regression models, birth weight z-score was significantly associated with IGFBP-1 in diabetic and normal pregnancies, and with IGFBP-3 in diabetic pregnancies.

CONCLUSION

Maternal diabetes is associated with suppressed levels of IGFBP-1 in cord serum, whereas those of IGFBP-3 do not change markedly. In diabetic pregnancies, both cord serum IGFBP-1 and IGFBP-3 correlate with fetal growth.

Effect of training on GH and IGF-1 responses to a submaximal exercise in football players

To study the effects of regular football training on basal and exercise induced levels of growth hormone (GH) and insulin-like growth factor (IGF-1), 13 young football players were investigated by a submaximal exercise at the beginning of the sporting season in October (S1), at the middle of the season in January (S2) and at the end in May (S3). At each session, an exercise test on an ergogycle was performed for 25 min, beginning with an incremental exercise to reach 90% of theoretical maximal heart, which was maintained for the last 10 min of the test. Venous blood samples were collected at rest, at the end of the exercise and at 30 and 60 min during the recovery period. Plasma lactate and glucose concentrations increased during exercise with no difference found between sessions. GH level increased with exercise at each session but the response was significantly higher in S1 than in S2 and S3 (P<0.01). The GH area under the curve decreased significantly all along the football season (P<0.01); the IGF-1 level did not significantly change during exercise nor with training. Basal insulin-like growth factor binding protein-3 (IGFBP3) remained stable during the three sessions. Football training decreased significantly the exercise-stimulated GH levels all along the football season but did not have any significant effect on IGF-1 levels or on basal IGFBP3 levels.

The effect of submaximal exercise on immuno- and bioassayable IGF-I activity in patients with GH-deficiency and healthy subjects

OBJECTIVE

Growth hormone (GH) increases during exercise, but the response of the insulin-like growth factor (IGF) system has not been as definitive. Therefore, we investigated the effect of the exercise-induced GH response on the circulating IGF-system in GH-deficient (GHD) and intact adults.

DESIGN

Eight GHD adults were studied on 2 occasions, with (+GH) and without (-GH) GH administered (0.4 IU) during exercise (45 min of cycle ergometer exercise at the lactate threshold). Eight age-matched controls were only studied on one occasion. Blood samples were drawn at baseline, during and post-exercise. IGFBP-3 proteolysis was measured by an in vitro proteolytic activity assay, IGF-I bioactivity by novel IGF-I kinase receptor activation assay (KIRA) and other hormones by immunoassay.

RESULTS

GH administration to GHD adults resulted in a serum GH peak similar to the exercise-stimulated GH response in GH intact controls, but exercise had only a small impact on the IGF system. IGF-I concentration was lower in controls but was only significantly lower than the +GH day. Neither IGF-I nor -II levels changed over time. IGFBP-1 demonstrated a time effect (P<0.01) in all groups, and a time x group interaction (P<0.01) with a rise at 75 min post-exercise, which was greater in the GHD subjects than controls. IGFBP-2 and -3 increased significantly (P<0.01) over time in the GHD subjects, but not in the controls. No change in IGFBP-3 proteolysis or IGF-I bioactivity was found during exercise or recovery in either group.

CONCLUSION

Submaximal exercise induced minor changes in IGFBP-1, -2 and -3, without affecting IGFBP-3 proteolysis and IGF-I bioavailability. Thus the metabolic status during submaximal exercise does not require a change in plasma IGF-I bioavailability. Administration of GH to GHD adults does not result in changes in proteolysis or bioavailability.

Exercise and circulating insulin-like growth factor I

Determinations of serum concentrations of total insulin-like growth factor I (tIGF-I) are important in the diagnosis, monitoring of treatment and safety evaluation of patients with growth disorders and/or metabolic disease. It is well established that tIGF-I status varies over time. Changes in tIGF-I levels in relation to an acute bout of exercise or repeated bouts, known as training, are likely to contribute to this variation. Serum tIGF-I has also been found to be of predictive value in growth prediction models employed before the start of growth hormone (GH) treatment. Furthermore, IGF-I generation tests have been suggested to be of value in the assessment of the growth response to GH administration in patients suspected of GH deficiency with or without some degree of GH insensitivity. This is discussed elsewhere in this issue. Recent progress in our understanding of growth hormone-dependent and -independent expression of the IGF1 gene in skeletal muscle and the role of sufficient energy intake during training for muscle and liver generation of IGF-I raises important questions regarding their relative contribution to the circulating pool of IGF-I. The present review is focused on circulating levels of tIGF-I in relation to a single bout of exercise or to a period of training. In addition, the expression of IGF-I locally in muscle in response to these stimuli will be discussed.

Human growth hormone responses to repeated bouts of sprint exercise with different recovery periods between bouts

This study examined the growth hormone (GH) response to repeated bouts of sprint cycling. Eight healthy men completed three trials consisting of two 30-s sprints on a cycle ergometer separated by either 60 min (Trial A) or 240 min (Trial B) of recovery and a single 30-s sprint carried out the day after Trial B (Trial C). Trials A and B were separated by at least 7 days. Blood samples were obtained at rest and during recovery from each sprint. In Trial A, GH was elevated immediately before sprint 2, and there was no further increase in GH following the second sprint [area under the curve: 460 (SD 348) vs. 226 min.mug(-1).l(-1) (SD 182), P = 0.05]. Free insulin-like growth factor I tended to be lower immediately before sprint 2 than sprint 1 (P = 0.06). Serum free fatty acids were not different immediately before each of the sprints. In Trial B, there was a trend for a smaller GH response to the second sprint [GH area under the curve: 512 (SD 396) vs. 242 min.mug(-1).l(-1) (SD 190), P = 0.09]. Free insulin-like growth factor I tended to be lower (P = 0.06), and serum free fatty acids were higher (P = 0.01) immediately before sprint 2 than sprint 1. There was no difference in the GH response to sprinting on consecutive days (Trials B and C). In conclusion, repeated bouts of sprint cycling on the same day result in an attenuation or even ablation of the exercise-induced increase in GH, depending on the recovery interval between sprints.

Influence of Nutrition on Responses to Resistance Training

A variety of dietary practices designed to enhance acute responses and chronic adaptations to resistance training have been examined with little consensus on the optimal nutritional approach for maximizing muscle and strength gains. From a scientific and practical perspective, the quantity, quality, and timing of nutrient ingestion around a workout are important factors to consider. Manipulation of exercise and nutritional variables can alter events that impact adaptations to training by a variety of mechanisms related to nutrient availability and uptake into tissues, hormonal secretion and interactions with receptors on target tissues, and gene transcription and translation of proteins that eventually impact protein, carbohydrate, and lipid metabolism. If the nutrition-mediated postresistance exercise change in any of these processes is of sufficient magnitude and duration, then over time an effect of muscle size, strength, and body composition is possible. To date, the majority of research has concentrated on providing carbohydrate alone or combined with protein before or after resistance exercise. Carbohydrate and protein intake significantly alters circulating metabolites and the hormonal milieu (i.e., insulin, testosterone, growth hormone, and cortisol), as well as the response of muscle protein and glycogen balance. The pathway of adaptation is proposed as a model to assist in integrating research findings from the current body of literature and future studies examining various diet and resistance exercise configurations.

Comparative studies on the regulation of insulin-like growth factor-binding protein-1 (IGFBP-1) and sex hormone-binding globulin (SHBG) production by insulin and insulin-like growth factors in human hepatoma cells

Production of insulin-like growth factor-binding protein-1 (IGFBP-1) by the liver is efficiently inhibited by insulin both in vivo and in vitro. Consequently, serum IGFBP-1 concentration reflects insulin bioactivity in portal vein. Sex hormone-binding globulin (SHBG) is another insulin-regulated liver-derived protein that has appeared promising in detecting individuals with portal hyperinsulinemia. We compared the regulation of IGFBP-1 and SHBG production by insulin and insulin-like growth factors (IGF-I and IGF-II) in human hepatoma cell cultures. Insulin equipotently inhibited IGFBP-1 and SHBG production, with maximal decrease in culture medium concentrations being about 35% for both proteins during 48 h of culture in serum-free medium. IGF-I and IGF-II also inhibited the IGFBP-1 and SHBG levels. We conclude that IGFBP-1 and SHBG are equally sensitive to ambient insulin concentrations in human hepatoma cell cultures, and the production of both proteins is also attenuated by the IGFs.

Training modalities: over-reaching and over-training in athletes, including a study of the role of hormones

BACKGROUND

An imbalance between the overall strain experienced during exercise training and the athlete's tolerance of such an effort may induce over-reaching (OR) or over-training syndrome (OTS). OR is characterized by an unexpected drop in performance despite increased training load or may lead to OTS, a complex state of exhaustion and persistent fatigue.

AIM

As it is important to adapt training modalities to the athletes' needs, and as there is still a lack of objective parameters suitable for the prevention and diagnosis of OTS, we studied 11 male elite cyclists, analysing the impact of training modalities ('training high-living low'; 'training low-living low') on exercise performance as well as on variable hormonal responses in order to detect early and sensitive markers for OR and/or OTS.

RESULTS

Although the variable hormones varied quite substantially among the two training groups, two ratios--free testosterone/cortisol (FTCR) and insulin-like growth factor-I/cortisol (IGF-I/C)--did not differ at all. This is important because athletes' final aim is to improve in an anabolic way. In addition, IGF-binding protein 3 (IGF-BP3) might be a useful screening factor for OR and OTS.

CONCLUSION

First, from a critical review of the existing over-training research, it must be concluded that there has been little improvement in recent years in the tools available for the diagnosis of OTS. Second, as variable training modalities do have a major impact on isolated hormones in circulation, hormonal ratios such as FTCR and IGF-I/C have to be calculated. These ratios might be useful parameters in the early detection of a imbalance between anabolic and catabolic metabolism.

Estradiol effects on the growth hormone/insulin-like growth factor-1 axis in amenorrheic athletes

Disruption of the growth hormone/insulin-like growth factor-1 (GH/IGF-1) axis has been reported and studied in menopause, hypothalamic amenorrhea, and anorexia nervosa, but not in weight-stable amenorrheic athletes. We investigated the effects of short-term transdermal estradiol on basal and exercise-stimulated serum GH, IGF-1, and associated binding proteins (IGFBP-1 and IGFBP-3) in seven weight-stable female amenorrheic athletes with percentage body fats greater that 12%. Each subject received a 72 h placebo patch followed by 144 h of transdermal estradiol. Serum samples for GH, IGF-1, IGFBP-1, and IGFBP-3 were obtained at baseline (t1), 72 hr (t2), 144 hr (t3), and during three 90-minute trials of aerobic exercise. Basal, and exercise GH, IGF-1, and IGFBP-1 were not different between trials. Baseline IGFBP-3 decreased from t1 to t2 (p = 0.04) and serum free fatty acids increased from t1 to t2, and t1 to t3 (p = 0.04, and 0.02 respectively). These findings differ from postmenopausal women, and women having weightloss-associated amenorrhea, suggesting that estrogen, exercise, and nutritional deficiencies may have independent effects on the GH/IGF-1 axis.

Influence of Acute Exercise on Urinary Protein, Creatinine, Insulin-Like Growth Factor-I (IGF-I) and IGF Binding Protein-3 Concentrations in Children

Insulin-like growth factor-I (IGF-I) is a polypeptide hormone and present in human urine. Insulin-like growth factor binding protein-3 (IGFBP-3) is the major form of binding protein in human circulation and functions as a carrier for IGF-I. Our goal was to determine the effects of volleyball exercise on the concentrations of urine protein, creatinine, IGF-I, and IGFBP-3 in children and to find out whether these effects differ between boys and girls. Volunteer children (13 females and 14 males), aged 10-13 years old were included in this work. Weight and height of the subjects were measured, and urine samples of their were collected before and after 2 hours of exercise. Urinary protein, creatinine, IGF-I and IGFBP-3 levels were analysed. Urinary protein, creatinine and IGF-I concentrations were increased after two hours of exercise wheres urinary IGFBP-3 concentrations did not change. In addition, no statistically significant difference in all parameters analysed was observed between boys and girls of similar age and body mass index.

Reduced IGFBP-1 is associated with thickening of the carotid wall in type 2 diabetes

OBJECTIVE

The aim of the present study was to assess the role of the insulin-like growth factor (IGF) system and lipids in predicting the carotid intima-media thickness (IMT) in type 2 diabetes.

RESEARCH DESIGN AND METHODS

A total of 239 type 2 diabetic participants in the Fenofibrate Intervention and Event Lowering in Diabetes (FIELD) Study (76 women) aged 50-75 years were examined before fenofibrate intervention. Patients underwent carotid ultrasonography for determination of IMT. IGF-I, IGF binding protein 1 (IGFBP-1), IGFBP-3, cholesterol, triglycerides, HDL cholesterol, LDL cholesterol, apolipoprotein B (apoB), lipoprotein(a) (Lp(a)), glucose, HbA(1c), and C-peptide were measured in fasting samples. Patients were divided in groups without (n = 168) and with (n = 71) clinical cardiovascular disease (CVD).

RESULTS

Partial correlations adjusted for age, sex, BMI, and diabetes duration showed an inverse association of IGFBP-1 with C-peptide (r = -0. 24, P = 0.018) and with maximal IMT (r = -0.42, P < 0.001), whereas IGF I and IGFBP-3 correlated positively with several risk-promoting lipid parameters. In linear regression analysis controlling for age, sex, BMI, diabetes duration, and presence or absence of oral antihyperglycemic or insulin medication, determinants of IMT were age, IGFBP-1, pulse pressure, Lp(a), diabetes duration, and insulin treatment. IGFBP-1 persisted in the model for subjects with CVD.

CONCLUSIONS

In summary, a decrease in IGFBP-1 is a marker of carotid IMT thickening in patients with type 2 diabetes.

IGF-I, IGFBP-2, and -3: do they have a role in detecting rhGH abuse in trained men?

PURPOSE

Although the illegal use of recombinant human growth hormone (rhGH) to enhance performance is increasing among athletes, no official test for its detection has yet been implemented. The aim of this work was to study how prolonged rhGH administration in trained subjects influences the insulin-like growth factor (IGF) system, in order to evaluate new methods in antidoping tests.

METHODS

Morning serum growth hormone (GH), IGF-I, IGF binding protein (BP)-2, IGFBP-3, IGF-I/IGFBP-2, and IGFBP-3/IGFBP-2 ratios were evaluated before, during (8th and 15th days), and at the end and after cessation (+3, +6, +9, +12, and +15 d) of a 3-wk treatment with different doses of rhGH (0.09 IU.kg BW(-1).d(-1) for 6 or 3 d a week, i.e., the A and B trials, respectively) in seven well-trained subjects not involved in competitive sports. The blood collections pre- and during treatment were performed immediately before the daily rhGH dose.

RESULTS

In both trials, significant increases of IGF-I (higher in the A trial) and IGFBP-3 serum concentrations during rhGH administration were observed. Serum IGFBP-3 remained significantly increased in the A trial 3 d after treatment cessation. In the A trial only, two subjects had IFG-I concentrations exceeding the upper limit of the reference range. No modifications of serum GH, IGFBP-2 and IGF-I/IGFBP-2, and IGFBP-3/IGFBP-2 ratios were observed. The z-score evaluation for IGFBP-3 detected GH exposure in 100% of subjects only at end treatment in A trial.

CONCLUSION

Although IGF-I and IGFBP-3 seem potentially the most specific markers of rhGH assumption, our data suggest that for antidoping purposes a single evaluation of their absolute serum concentration is not a sufficiently secure method to detect rhGH abuse in all subjects, especially in the case of low rhGH doses.

Evidence that the decrease in liver glycogen is associated with the exercise-induced increase in IGFBP-1

The purpose of the present study was to test the hypothesis that the exercise-induced increase in insulin-like growth factor binding protein (IGFBP)-1 is not always linked to a decrease in blood glucose level and to examine whether the decreasing levels of liver glycogen during exercise may be associated with the increase in IGFBP-1. Three groups of rats were submitted to a 70-min treadmill exercise. One group of rats was fed normally, and the two other groups had their food intake restricted by 50% (50% fast) the night before the experiment. One of these two 50% fasted groups of rats was infused (intravenously) with glucose throughout exercise to maintain euglycemia. Exercise in noninfused 50% fasted rats, compared with the normally fed rats, resulted in significantly lower blood glucose (minute 70) and insulin levels, significantly lower liver glycogen content, no change in IGF-I, and significantly higher increases in free fatty acid, glycerol, beta-hydroxybutyrate, and IGFBP-1. Maintenance of euglycemia during exercise in glucose-infused 50% fasted rats reduced to a large extent the decrease in insulin levels but only slightly attenuated the lipid response and the IGFBP-1 response seen in noninfused 50% fasted rats. Comparisons of all individual liver glycogen and IGFBP-1 values revealed that liver glycogen values were highly (P < 0.001) predictive of the IGFBP-1 response during exercise (R = 0.564). The present results indicate that the IGFBP-1 response during exercise is not always linked to a decrease in plasma glucose and suggest that the increase in IGFBP-1 during exercise may be related to the decrease in liver glycogen content.

Fitness, acute exercise, and anabolic and catabolic mediators in cystic fibrosis

Exercise can stimulate catabolic inflammatory cytokines even in healthy children. For patients with cystic fibrosis (CF), this may be problematic because CF is characterized by increased inflammation and suppressed growth. We examined fitness and the response to brief exercise of interleukin-6 (IL-6), tumor necrosis factor-alpha (TNF-alpha), insulinlike growth factor-I (IGF-I), and IGF binding protein-1 (IGFBP-1) in 14 subjects with CF (10.5 +/- 0.8 yr of age), 9 of whom were treated with ibuprofen, and 14 healthy control subjects (11.6 +/- 0.5 yr of age, NS). Subjects performed brief intermittent, constant work rate protocol (scaled to each individual's exercise capacity) with blood and urine sampling. Peak V O(2) was correlated with IGF-I (r = 0.68, p < 0.01) in control subjects but not in subjects with CF. In subjects with CF, baseline IL-6 was 79% greater (p < 0.05) and IGF-I was 47% lower than in control subjects (p < 0.05). Post hoc analysis revealed a progressive increase in the IL-6 response to exercise, with the lowest increase observed in control subjects (11.8 +/- 4.6 pg/L/kJ), higher increases in patients with CF treated with ibuprofen (23.4 +/- 7.7 pg/L/kJ), and highest in subjects with CF not receiving ibuprofen (29.2 +/- 7.5 pg/L/kJ). Qualitatively similar results were observed for TNF-alpha. Exercise also significantly increased IGFBP-1 in both control subjects and subjects with CF. Brief exercise can increase even chronically elevated inflammatory mediators in CF, and this response may be attenuated by ibuprofen.

Effects of an endurance cycling competition on resting serum insulin-like growth factor I (IGF-I) and its binding proteins IGFBP-1 and IGFBP-3

OBJECTIVES

To determine whether consecutive bouts of intense endurance exercise over a three week period alters serum concentrations of insulin-like growth factor I (IGF-I) and/or its binding proteins.

METHODS

Seventeen professional cyclists (mean (SEM) VO(2)MAX, 74.7 (2.1) ml/kg/min; age, 27 (1) years) competing in a three week tour race were selected as subjects. Blood samples were collected at each of the following time points: t(0) (control, before the start of competition), t(1) (end of first week), and t(3) (end of third week). Serum levels of both total and free IGF-I and IGF binding proteins 1 and 3 (IGFBP-1 and IGFBP-3) were measured in each of the samples. Cortisol levels were measured in nine subjects.

RESULTS

A significant (p<0.01) increase was found in total IGF-I and IGFBP-1 at both t(1) and t(3) compared with t(o) (IGF-I: 110.9 (17.7), 186.8 (12.0), 196.9 (14.7) ng/ml at t(0), t(1), and t(3) respectively; IGFBP-1: 54.6 (6.6), 80.6 (8.0), and 89.2 (7.9) ng/ml at t(0), t(1), and t(3) respectively). A significant (p<0.01) decrease was noted in free IGF-I at t(3) compared with both t(o) and t(1) (t(0): 0.9 (0.1) ng/ml; t(1): 0.9 (0.1) ng/ml; t(3): 0.7 (0.1) ng/ml); in contrast, IGFBP-3 levels remained stable throughout the race.

CONCLUSIONS

It would appear that the increase in circulating levels of both IGF-I and its binding protein IGFBP-1 is a short term (one week) endocrine adaptation to endurance exercise. After three weeks of training, total IGF-I and IGFBP-1 remained stable, whereas free IGF-I fell below starting levels.

Time course changes in IGFBP-1 after treadmill exercise and postexercise food intake in rats

Prolonged exercise increases circulating insulin-like growth factor binding protein-1 (IGFBP-1) in humans and animals, but its physiological significance is unknown. This study examined 1) time-course changes in plasma IGFBP-1 and hepatic IGFBP-1 mRNA expression after exercise, 2) changes in IGFBP-1 in relation to plasma glucose, insulin, and IGF-I, and 3) the impact of feeding a postexercise meal on the IGFBP-1 response. Food-deprived male rats were vigorously run on a treadmill and compared with nonexercised controls at 15 min and 1, 4, 8, and 12 h after exercise. Circulating insulin concentrations in exercised rats were lower than in controls at 15 min and 1 h, whereas plasma glucose and IGF-I remained unaffected. Circulating and hepatic expression of IGFBP-1 was markedly increased above that of controls at 15 min, 1 h, and 12 h. In a separate experiment, one-half of the exercised animals received a nutritionally complete meal immediately after the experimental run. The meal elevated plasma insulin and glucose concentrations at 15 min and 1 h. Despite this change in nutritional status, serum IGFBP-1 concentrations and hepatic IGFBP-1 abundance remained elevated at 15 min and 1 h. These results demonstrate that the IGFBP-1 response to a single bout of treadmill exercise is short in duration and independent of insulin, glucose, and amino acid availability.

Increased pulsatility, process irregularity, and nocturnal trough concentrations of growth hormone in amenorrheic compared to eumenorrheic athletes

Amenorrheic athletes exhibit a spectrum of neuroendocrine disturbances, including alterations in the GH-insulin-like growth factor I (IGF-I) axis. Whether these changes are due to exercise or amenorrhea is incompletely characterized. The present study investigates spontaneous (overnight) and exercise-stimulated GH secretion and associated IGF-binding proteins (IGFBPs) in amenorrheic (AA; n = 5), and eumenorrheic athletes ( n = 5) matched for age, percent body fat (dual energy x-ray absorptiometry), training history, and maximal oxygen consumption. Each volunteer participated in two hospital admissions consisting of a 50-min submaximal exercise bout (70% maximal oxygen consumption) and an 8-h nocturnal sampling period. Deconvolution analysis of serum GH concentration time series revealed increases in the half-life of GH (60%) and the number of secretory bursts (85%) as well as a decrease in their half-duration (50%) and the mass of GH secreted per pulse (300%) in the AA cohort. Time occupancy at elevated trough GH concentrations was significantly increased, and GH pulsatility (approximate entropy) was more irregular in the AA group. During exercise, AA exhibited a reversal of the normal relationship between IGF-I and GH, and a 4- to 5-fold blunting of stimulated peak and integrated GH secretion. Fasting levels of plasma IGF-I, IGFBP-3, and IGFBP-1 appeared to be unaffected by menstrual status. In ensemble, this phenotype of GH release in amenorrheic athletes suggests disrupted neuroregulation of episodic GH secretion, possibly reflecting decreased somatostinergic inhibition basally, and reduced GHRH output in response to exercise compared with eumenorrheic athletes. Accordingly, we postulate that the amenorrheic state, beyond the exercise experience per se, alters the neuroendocrine control of GH output in amenorrheic athletes.