GH response to exercise: assessment of the pituitary refractory period, and relationship with circulating components of the GH-IGF-I axis in adolescent females

Prevalence of refractoriness when testing growth hormone levels in children

OBJECTIVE

Late night spontaneous growth hormone (GH) pulses may influence the pituitary GH response to provocation tests. We evaluated GH response during arginine-insulin-tolerance test (AITT) after a GH peak during a short spontaneous nocturnal profile (SSNP) in children with short stature or low growth velocity.

DESIGN

Using SSNP and subsequent AITT, we examined 257 children 4-18 years old (138 (53.7%) males) recruited from three hospitals. Medical records were reviewed retrospectively. Refractory children were defined as a GH peak ≥7 μg/L during SSNP but no GH peak ≥7 μg/L during AITT.

RESULTS

In total, 201/257 children had a GH peak ≥7 μg/L at SSNP and/or AITT. Of these, 21.9% were refractory. The proportion of males (p = 0.033) and body mass index (BMI) standard deviation score (SDS) (p = 0.037) were higher in the refractory group than in children with a GH peak ≥7 μg/L during AITT. The median period between last GH peak ≥7 μg/L during SSNP and GHmax at AITT was 210 (30-390) minutes. The GHmax at AITT occurred 30 min earlier for children without a peak ≥7 μg/L during the SSNP (p = 0.004). The number of refractoriness differed somewhat between the hospitals (p = 0.025).

CONCLUSIONS

Many children with short stature were refractory at testing; among them we found few clinical characteristics. Refractoriness might be influenced by some differences in procedure, but needs to be considered when evaluating GH response in children.

High-intensity interval exercise test stimulates growth hormone secretion in children

BACKGROUND

exercise stimulates growth hormone (GH) secretion and may serve as a promising physiological test for the diagnosis of GH deficiency. However, exercise standardization for a feasible GH test is still lacking. The aim of the present study was to examine the GH secretion to high intensity interval exercise.

METHODS

Seventeen children (12.4 ± 2.6 years) with impaired growth rate performed high-intensity interval exercise test (HIIE) that included 10 intervals of 15 s all out pedaling against resistance determined by age, sex and weight on a cycle ergometer with 1-min active rest between each interval. Power output measurements were collected during the test. Blood samples were collected before, immediately after, 30, 45, and 60min after the beginning of the exercise test. GH response was compered to pharmacological provocation test (clonidine or glucagon).

RESULTS

HIIE led to a significant increase in GH levels (p < 0.001), with high correlation to GH response following pharmacological stimulation (r = 0.82, r = 0.80 for clonidine and glucagon respectively, p < 0.001) A significant correlation was found between mean peak power to body weight and the GH response (r = 0.50, p = 0.04). 83% of the participants who reached peak power > 10 watts/kg had normal GH secretion.

CONCLUSIONS

HIIE is a brief and individualized exercise protocol that may be used as a physiological provocation test for GH secretion. There might be a minimum of anaerobic power needed to induce adequate GH response during HIIE.

Discordance Between Stimulated and Spontaneous Growth Hormone Levels in Short Children Is Dependent on Cut-Off Level and Partly Explained by Refractoriness

BACKGROUND

A growth hormone (GH) stimulation test is the recommended method for evaluating GH levels in children with possible GH deficiency (GHD). However, serial measurements of nocturnal spontaneous GH secretion are also performed. Divergent results from these tests have been reported, but with variable frequencies.

OBJECTIVES

To investigate whether performing one or two GH tests is associated with the probability to diagnose a child with GHD; the frequency of divergent results in the arginine-insulin tolerance test (AITT) and the nocturnal spontaneous test using different cut-off levels, and whether refractoriness may explain some of the discordance.

METHODS

In a population-based setting, the medical records of all short children evaluated for possible GHD during January 1993-February 2017 were reviewed. Twenty-one patients had been evaluated with one GH test only and 102 children had been evaluated with a spontaneous nocturnal GH test followed immediately by a complete AITT. Divergent results were defined as having a pathological response on only one of the tests when using 3, 5, 7, and 10 µg/L as cut-offs for peak GH on both tests, 1.1 and 3.3 µg/L for mean nocturnal values and receiver operating characteristic curves-derived cut-offs for nocturnal values.

RESULTS

Children evaluated with one test only were more often diagnosed with GHD compared with children evaluated with both tests (48 vs. 19%, p = 0.019). Divergent results were found in 6-42% of the patients, with higher frequencies seen when higher cut-offs were applied. A higher proportion of patients with stimulated peak values ≤ 7 and ≤ 5 µg/L had a spontaneous peak within 2 h before the start of the AITT compared with patients with higher stimulated peak values (68 vs. 45%, p = 0.026, and 77 vs. 48%, p = 0.033, respectively).

CONCLUSIONS

Divergent results between AITT and nocturnal spontaneous secretion are common in short children, dependent on the cut-offs applied and partly due to refractoriness. Performing both tests decreases the risk of over diagnosing GHD in short children.

Effects of aquatic exercise and CES treatment on the changes of cognitive function, BDNF, IGF-1, and VEGF of persons with intellectual disabilities

[Purpose]

The purpose of this study was to investigate the effects of aquatic exercise and CES treatment on the cognitive function by using K-WAB and BDNF, IGF-1, and VEGF of persons with intellectual disabilities.

[Methods]

All subjects were 15 male with intellectual disabilities who were participating in the aquatic training program and CES treatment during 12 weeks at rehabilitation center. The subjects were divided into control group, exercise group, and exercise+CES group. Blood samples for BDNF, IGF-1, and VEGF were taken from brachial vein at rest between before and after treatment.

[Results]

The results are summarized as follows: Cognitive function level increased significantly in the exercise+CES group compared to those in the exercise and control group. The changes of blood IGF-1 concentration were no significant difference among groups. The changes of blood BDNF and VEGF concentration were significantly increased in exercise group and exercise+CES group than control group. However, blood BDNF and VEGF concentration were significantly difference between exercise group and exercise+CES group.

[Conclusion]

In conclusion, it can be concluded that CES treatment with exercise can amend cognitive function of persons with intellectual disabilities more effectively and increase of BDNF and VEGF by exercise can explain the cognitive function improvement of persons with intellectual disabilities.

Exercise modulates insulin-like growth factor 1-dependent and -independent effects on adult hippocampal neurogenesis and behaviour

While physical exercise clearly has beneficial effects on the brain, fomenting neuroprotection as well as promoting neural plasticity and behavioural modifications, the cellular and molecular mechanisms mediating these effects are not yet fully understood. We have analyzed sedentary and exercised animals to examine the effects of activity on behaviour (spatial memory and anxiety--as measured by a fear/exploration conflict test), as well as on adult hippocampal neurogenesis (a well-known form of neural plasticity). We have found that the difference in activity between sedentary and exercised animals induced a decrease in the fear/exploration conflict scores (a measure usually accepted as an anxiolytic effect), while no changes are evident in terms of spatial memory learning. The short-term anxiolytic-like effect of exercise was IGF1-dependent and indeed, the recall of hippocampus-dependent spatial memory is impaired by blocking serum IGF1 (as observed by measuring serum IGF levels in the same animals used to analyze the behaviour), irrespective of the activity undertaken by the animals. On the other hand, activity affected neurogenesis as reflected by counting the numbers of several cell populations, while the dependence of this effect on IGF1 varied according to the differentiation state of the new neurons. Hence, while proliferating precursors and postmitotic immature neurons (measured by means of doublecortin and calretinin) are influenced by serum IGF1 levels in both sedentary and exercised animals, premitotic immature neurons (an intermediate stage) respond to exercise independently of serum IGF1. Therefore, we conclude that physical exercise has both serum IGF1-independent and -dependent effects on neural plasticity. Furthermore, several effects mediated by serum IGF1 are induced by physical activity while others are not (both in terms of behaviour and neural plasticity). These findings help to delimit the role of serum IGF1 as a mediator of the effects of exercise, as well as to extend the role of serum IGF1 in the brain in basal conditions. Moreover, these data reveal the complexity of the interaction between neurogenesis, behaviour, and IGF1 under different levels of physical activity.

Immunological and growth mediator response to cross-country training in adolescent females

BACKGROUND

Exercise affects growth and development through a complex interaction between the endocrine, immune, and nervous systems. To date very little is known about how these systems respond to exercise in children or adolescents. Moreover, there are few studies that have examined growth factors, pro-inflammatory cytokines, and peripheral blood mononuclear cell responses to 'real-life' or field exercise solely in girls.

AIM

To determine the acute exercise-induced alterations in the growth hormone (GH)-insulinlike growth factor-I (IGF-I) axis, inflammatory cytokines, and certain aspects of immune function (white blood cell [WBC] subpopulations and their associated adhesion molecules) in a group of adolescent girls following a typical cross country practice.

METHODS

Eight, healthy, postpubertal, high school females, 15-18 years old, performed a single, typical, one hour cross-country practice session. Blood was sampled before and after the session.

RESULTS

Following exercise, lactate increased by 364 +/- 67% (p < 0.001). Significant increases were noted in circulating IL-6 (p < 0.023), TNF-alpha (p < 0.027), IL-1beta (p < 0.047) and IL-1ra (p < 0.002), as well as a substantial increase in GH (p < 0.007). The exercise led to significant increases in all WBC subpopulations and platelets. The most significant changes were observed for natural killer cells (p < 0.0005). The exercise significantly influenced adhesion molecules (such as CD62L, CD54).

CONCLUSIONS

These data demonstrate that an intense exercise bout in adolescent females leads to profound increases in inflammatory cytokines, with substantial changes in WBC and adhesion molecules. The role of these frequent, almost-daily perturbations on growth, development and immunity has yet to be determined.

Effect of water polo practice on cytokines, growth mediators, and leukocytes in girls

PURPOSE

The effects of exercise on growth and development are mediated through a complex interaction between the endocrine, immune, and nervous systems. Very little is known about how these systems respond to exercise in children or adolescents. Moreover, there are few studies that have examined growth factors, inflammatory cytokines, and leukocyte responses to "real-life" or field exercise solely in girls. Thus, the goal of the present study was to determine the acute exercise-induced alterations in the growth hormone --> insulin-like growth factor-I axis, inflammatory cytokines, and certain aspects of immune function in a group of adolescent girls after a typical water polo practice.

METHODS

Ten, healthy, high-school female subjects, 14-16 yr old, performed a single, typical, 1.5-h water polo practice session. Blood was sampled before and after the session.

RESULTS

The exercise resulted in an increase in HR (from 82 +/- 2 to 161 +/- 5 beats.min(-1) at 30 min, P < 1.4.10(-6) ), as well as in circulating lactate levels (375 +/- 66%, P < 0.0005). Significant increases where noted in circulating IL-6 (396 +/- 162%, P < 0.005) and IL-1ra (71 +/- 20%, P < 0.015). A substantial increase in the level of IGFBP-1 (1344 +/- 344%, P < 0.001) was also observed. Interestingly, TNF-alpha levels decreased after the exercise (-10.4 +/- 3.8%, P < 0.04) as did insulin (55 +/- 12%, P < 0.005). The exercise led to significant increases in granulocytes, monocytes, and lymphocytes. The exercise significantly influenced adhesion molecules (such as CD62L and CD54), which has not been previously studied in adolescent girls.

CONCLUSIONS

These data demonstrate that an intense "real-life" exercise bout in adolescent females leads to profound increases in inflammatory cytokines and reductions in anabolic mediators with substantial alterations in white blood cell subpopulations and adhesion molecules. The role of these frequent, almost daily immune and cytokine changes on growth and development have yet to be determined.