Sex non-specific growth charts and potential clinical implications in the care of transgender youth

Introduction

The Centers for Disease Control and Prevention (CDC) and World Health Organization (WHO) created separate growth charts for girls and boys because growth patterns and rates differ between sexes. However, scenarios exist in which this dichotomizing "girls versus boys" approach may not be ideal, including the care of non-binary youth or transgender youth undergoing transitions consistent with their gender identity. There is therefore a need for growth charts that age smooth differences in pubertal timing between sexes to determine how youth are growing as "children" versus "girls or boys" (e.g., age- and sex-neutral, compared to age- and sex-specific, growth charts).

Methods

Employing similar statistical techniques and datasets used to create the CDC 2000 growth charts, we developed age-adjusted, sex non-specific growth charts for height, weight, and body mass index (BMI), and z-score calculators for these parameters. Specifically, these were created using anthropometric data from five US cross-sectional studies including National Health Examination Surveys II-III and National Health and Nutrition Examination Surveys I-III. To illustrate contemporary clinical practice, we overlaid our charts on CDC 2000 girls and boys growth charts.

Results

39,119 youth 2-20 years old (49.5% female; 66.7% non-Hispanic White; 21.7% non-Hispanic Black) were included in the development of our growth charts, reference ranges, and z-score calculators. Respective curves were largely superimposable through around 10 years of age after which, coinciding with pubertal onset timing, differences became more apparent.

Discussion

We conclude that age-adjusted, sex non-specific growth charts may be used in clinical situations such as transgender youth in which standard "girls versus boys" growth charts are not ideal. Until longitudinal auxological data are available in these populations, our growth charts may help to assess a transgender youth's growth trajectory and weight classification, and expectations surrounding these.

Emotional Deprivation in Children: Growth Faltering and Reversible Hypopituitarism

Emotional deprivation can lead to growth faltering of infants and children. The mechanism(s) involved differ in that for infants, the major metabolic problem is inadequate energy intake for growth. In young children, it is likely that the emotional deprivation causes a syndrome not only of growth faltering, but with bizarre behaviors, especially with regard to food: hoarding, gorging and vomiting, hyperphagia, drinking from the toilet, and eating from garbage pails. Other disturbed behaviors include, poor sleep, night wanderings, and pain agnosia. The pathophysiology appears to be reversible hypopituitarism, at least for the growth hormone and hypothalamic-pituitary- adrenal axes. The review begins with an historical perspective concerning stress, children and growth and then moves to the issue of hospitalism, where young infants failed to thrive (and died) due to inadequate stimulation and energy intake. Refeeding programs at the end of World Wars I and II noted that some children did not thrive despite an adequate energy intake. It appeared that in addition taking care of their emotional needs permitted super-physiologic (catch-up) growth. Next came the first notions from clinical investigation that hypopituitarism might be the mechanism of growth faltering. Studies that address this mechanism from a number of observational and clinical research studies are reviewed in depth to show that the hypopituitarism was relieved upon removal from the deprivational environment and occurred much too quickly to be due to adequate energy alone. These findings are then compared to those from malnourished children and adoptees from emerging countries, especially those from orphanages where their psychosocial needs were unmet despite adequate caloric intake. Together, these various conditions define one aspect of the field of psychoneuroendocrinology.

Use of Gonadotropin-Releasing Hormone Analogs in Children: Update by an International Consortium

This update, written by authors designated by multiple pediatric endocrinology societies (see List of Participating Societies) from around the globe, concisely addresses topics related to changes in GnRHa usage in children and adolescents over the last decade. Topics related to the use of GnRHa in precocious puberty include diagnostic criteria, globally available formulations, considerations of benefit of treatment, monitoring of therapy, adverse events, and long-term outcome data. Additional sections review use in transgender individuals and other pediatric endocrine related conditions. Although there have been many significant changes in GnRHa usage, there is a definite paucity of evidence-based publications to support them. Therefore, this paper is explicitly not intended to evaluate what is recommended in terms of the best use of GnRHa, based on evidence and expert opinion, but rather to describe how these drugs are used, irrespective of any qualitative evaluation. Thus, this paper should be considered a narrative review on GnRHa utilization in precocious puberty and other clinical situations. These changes are reviewed not only to point out deficiencies in the literature but also to stimulate future studies and publications in this area.

Natesto™ , a novel testosterone nasal gel, normalizes androgen levels in hypogonadal men

Advantages of testosterone nasal gel include ease of administration, low dose, and no risk of secondary transference. The efficacy and safety of testosterone nasal gel was evaluated in hypogonadal males. The ninety-day, randomized, open-label, dose-ranging study, included potential dose titration and sequential safety extensions to 1 year. At 39 US outpatient sites, 306 men (mean age 54.4 years) with two fasting morning total serum testosterone levels <300 ng/dL were randomized (n = 228, b.i.d. dosing; n = 78, t.i.d. dosing). Natesto(™) Testosterone Nasal Gel was self-administered, using a multiple-dose dispenser, as two or three daily doses (5.5 mg per nostril, 11.0 mg single dose). Total daily doses were 22 mg or 33 mg. The primary endpoint was the Percentage of patients with Day-90 serum total testosterone average concentration (C(avg)) value within the eugonadal range (≥300 ng/dL, ≤1050 ng/dL). At Day 90, 200/273 subjects (73%; 95% CI 68, 79) in the intent-to-treat (ITT) population and 180/237 subjects (76%; 71, 81) in the per-protocol (PP) population were in the normal range. Also, in the normal range were 68% (61, 74) of ITT subjects and 70% (63, 77) of PP subjects in the titration arm, as well as, 90% (83, 97) of ITT subjects and 91% (84, 98) of PP subjects in the fixed-dose arm. Natesto(™) 11 mg b.i.d. or 11 mg t.i.d. restores normal serum total testosterone levels in most hypogonadal men. Erectile function, mood, body composition, and bone mineral density improved from baseline. Treatment was well tolerated; adverse event rates were low. Adverse event discontinuation rates were 2.1% (b.i.d.) and 3.7% (t.i.d.). This study lacked a placebo or an active comparator control which limited the ability to adequately assess some measures.

[Insulin growth factor-I-based dosing of growth hormone therapy in children: a randomized, controlled study]

Weight-based dosing of growth hormone (GH) is the standard of therapy in short children although insulin-like growth factor-I (IGF-I) is a major mediator of GH actions on growth. Objective: to test whether the IGF-I levels achieved during GH therapy are determinants of the growth responses to GH therapy. This was a two-year open-label, randomized IGF-I concentration-controlled trial. Prepubertal short children [n = 172; mean age 7.53 years; mean height SD score (HT-SDS - 2.64] with low IGF-I levels (mean IGF-I SDS - 3.56) were randomized to receive one of two GH dose-titration arms in which GH dosage was titrated to achieve an IGF-I SDS at the mean [IGF(low) group, n = 70) or the upper limit of the normal range [+2 SDS, IGF(high) group, n = 68] or to a comparison group of conventional GH dose of 40 mg/kg/day (n = 34). The multicenter study was performed in the outpatient centers. The primary outcome measure was to determine changes in HT-SDS during 2-year therapy. One hundred and forty-seven patients completed the trial. Target IGF-I levels were achieved in the dose-titration arms within 6-9 months. The changes in HT-SDS were +1.0, +1.1, and +1.6 for conventional, IGF(low), and IGF(high), respectively, with IGF(high) showing significantly greater linear growth response (p < 0.001), compared with the two other groups). The IGF-I(high) arm required higher doses ( > 2.5 times) than the IGF-I(low) arm, and these GH doses were highly variable (20-346 mg/kg/day). Multivariate analyses suggest that the rise in IGF-I SDS significantly impacted height outcome along with the GH dose and the pretreatment peak-stimulated GH level. IGF-I-based GH dosing is clinically feasible and allows maintaining serum IGF-I concentrations within the desired target range. Titrating the GH dose to achieve higher IGF-I target results in improved growth responses, although at higher average GH doses.

Consensus statement on the diagnosis and treatment of children with idiopathic short stature: a summary of the Growth Hormone Research Society, the Lawson Wilkins Pediatric Endocrine Society, and the European Society for Paediatric Endocrinology Workshop

OBJECTIVE

Our objective was to summarize important advances in the management of children with idiopathic short stature (ISS).

PARTICIPANTS

Participants were 32 invited leaders in the field.

EVIDENCE

Evidence was obtained by extensive literature review and from clinical experience.

CONSENSUS

Participants reviewed discussion summaries, voted, and reached a majority decision on each document section.

CONCLUSIONS

ISS is defined auxologically by a height below -2 sd score (SDS) without findings of disease as evident by a complete evaluation by a pediatric endocrinologist including stimulated GH levels. Magnetic resonance imaging is not necessary in patients with ISS. ISS may be a risk factor for psychosocial problems, but true psychopathology is rare. In the United States and seven other countries, the regulatory authorities approved GH treatment (at doses up to 53 microg/kg.d) for children shorter than -2.25 SDS, whereas in other countries, lower cutoffs are proposed. Aromatase inhibition increases predicted adult height in males with ISS, but adult-height data are not available. Psychological counseling is worthwhile to consider instead of or as an adjunct to hormone treatment. The predicted height may be inaccurate and is not an absolute criterion for GH treatment decisions. The shorter the child, the more consideration should be given to GH. Successful first-year response to GH treatment includes an increase in height SDS of more than 0.3-0.5. The mean increase in adult height in children with ISS attributable to GH therapy (average duration of 4-7 yr) is 3.5-7.5 cm. Responses are highly variable. IGF-I levels may be helpful in assessing compliance and GH sensitivity; levels that are consistently elevated (>2.5 SDS) should prompt consideration of GH dose reduction. GH therapy for children with ISS has a similar safety profile to other GH indications.

Idiopathic short stature: definition, epidemiology, and diagnostic evaluation

Idiopathic short stature is a condition in which the height of the individual is more than 2 SD below the corresponding mean height for a given age, sex and population, in whom no identifiable disorder is present. It can be subcategorized into familial and non-familial ISS, and according to pubertal delay. It should be differentiated from dysmorphic syndromes, skeletal dysplasias, short stature secondary to a small birth size (small for gestational age, SGA), and systemic and endocrine diseases. ISS is the diagnostic group that remains after excluding known conditions in short children.

Idiopathic short stature: management and growth hormone treatment

In the management of ISS auxological, biochemical, psychosocial and ethical elements have to be considered. In boys with constitutional delay of growth and puberty androgens are effective in increasing height and sexual characteristics, but adult height is unchanged. GH therapy is efficacious in increasing height velocity and adult height, but the inter-individual variation is considerable. The effect on psychosocial status is uncertain. Factors affecting final height gain include GH dose, height deficit in comparison to midparental height, age and first year height velocity. In case of a low predicted adult height at the onset of puberty, addition of a GnRH analogue can be considered. Although GH therapy appears safe, long-term monitoring is recommended.

Rh/IGF-I/rhIGFBP-3 administration to patients with type 2 diabetes mellitus reduces insulin requirements while also lowering fasting glucose

Administration of insulin-like growth factor-I to patients with diabetes enhances insulin action and reduces the degree of hyperglycemia but it is associated with a high rate of adverse events. Infusion of the combination of rhIGFBP-3 (the principal binding protein for IGF-I in plasma) with rhIGF-I to patients with type I diabetes improved insulin sensitivity and was associated with a low incidence in side effects. In this study, 52 patients with insulin-treated type 2 diabetes received recombinant human IGF-I plus rhIGFBP-3 in one of four dosage regimens for 14 days. The four groups were: (1) continuous subcutaneous infusion of 2 mg/kg/day; (2) the same 2 mg/kg dose infused subcutaneously over 6 h between 2000 and 0200 h; (3) 1 mg/kg twice a day by bolus subcutaneous injection; (4) a single bedtime subcutaneous injection of 1 mg/kg. Across these four groups rhIGF-I/rhIGFBP-3 decreased insulin requirements between 54% and 82%. Fasting glucose decreased by 32-37%. Mean daily blood glucose (4 determinations per day) declined in all 4 groups (range 9-23% decrease). Frequent sampling for total IGF-I, free IGF-I and IGFBP-3 was performed on days 0,1,7,14 and 15. The peak total IGF-I values were increased to 4.0-4.8-fold at 16-24 h. For free IGF-I the increase varied between 7.1 and 8.2-fold and peak values were attained at 16-20 h after administration. Both the time to maximum concentration (Tmax) and the maximum free IGF-I levels (Cmax) on day 1 for all groups were substantially less than previously published studies, wherein lower doses of rhIGF-I were given without IGFBP-3. The improvement in glucose values and the degree of reduction in insulin requirement were the greatest in groups 2 and 3 and the patients in those groups had the highest free IGF-I levels. The frequency of side effects such as edema, jaw pain and arthralgias was 4% which is less than that has been reported in previous studies wherein IGF-I was administered without IGFBP-3. We conclude that rhIGF-I/rhIGFBP-3 significantly lowers insulin requirements yet improves glucose values and these changes may reflect improvement in insulin sensitivity. Coadministration of IGFBP-3 with IGF-I produces lower free IGF-I (Tmax and Cmax) levels compared to administration of IGF-I alone and is associated with relatively low incidence of side effects during 2 weeks of administration.

Growth, body composition and hormonal axes in children and adolescents

Growth and physical maturation are dynamic processes that encompass a broad range of cellular and somatic changes. Most investigators who study growth have focused on linear growth (change in height over time), but alterations in the relative body proportions, body composition, and the regional distribution of body fat (upper body vs lower body, axial vs appendicular, and sc vs deep visceral) are essential elements for growth and sexual maturation. In fact, cardiovascular risk assessment in the adult relies heavily on the regional distribution of body fat. The antecedents for the adult pattern of fat are clearly present in the adolescent, if not the younger child. Standards for each of these parameters have been developed for multiple ethnic and racial populations and aid materially in the identification of children with normal growth and physical development, variations within the broad normal (physiological) range, and those with clearly pathological growth patterns.

Accelerated escape from GH autonegative feedback in midpuberty in males: evidence for time-delimited GH-induced somatostatinergic outflow in adolescent boys

A single injected pulse of GH inhibits the time-delayed secretion of GH in the adult by way of central mechanisms that drive somatostatin and repress GHRH outflow. The marked amplification of spontaneous GH pulse amplitude in puberty poses an autoregulatory paradox. We postulated that this disparity might reflect unique relief of GH-induced autonegative feedback during this window of development. The present study contrasts GH autonegative feedback in: 1) normal prepubertal boys (PP) (n = 6; Tanner genital stage I, chronologically aged 8 yr, 9 months to 10 yr, 1 month; median bone age 8.5 yr); 2) longitudinally identified midpubertal boys (MP) (n = 6; Tanner genital stages III/IV, aged 12 yr, 6 months to 15 yr, 6 months; median bone age 15 yr); and 3) healthy young men (YM) (n = 6, aged 18-24 yr; bone age >18 yr). Subjects each underwent four randomly ordered tandem peptide infusions on separate mornings while fasting: i.e. 1) saline/saline infused iv bolus at 0830 h and 1030 h; 2) saline/GHRH (0.3 microg/kg i.v. bolus) at the foregoing times; 3) recombinant human (rh) GH (3 microg/kg as a 6-min square-wave i.v. pulse)/saline; and 4) rhGH and GHRH. To monitor GH autofeedback effects, blood samples were obtained every 10 min for 5.5 h beginning at 0800 h (30 min before GH or saline infusion). Serum GH concentrations were quantitated by ultrasensitive chemiluminometry (threshold 0.005 microg/liter). On the day of successive saline/saline infusion, MP boys maintained higher serum concentrations of: 1) GH ( microg/liter), 2.2 +/- 0.25, compared with PP (0.61 +/- 0.10) or YM (0.88 +/- 0.36) (P = 0.011); 2) IGF-I ( micro g/liter), 493 +/- 49 vs. PP (134 +/- 16) and YM (242 +/- 22) (P < 0.001); 3) T (ng/dl), 524 +/- 58 vs. PP (<20) (P < 0.001); and 4) E2 (pg/ml),19 +/- 3 vs. PP (< 10) (P = 0.030) (mean +/- SEM). Consecutive saline/GHRH infusion elicited comparable peak (absolute maximal) serum GH concentrations (micrograms per liter) in the three study groups, i.e. 18 +/- 5.0 (PP), 9.6 +/- 1.7 (MP), and 14 +/- 5.3 (YM) (each P < 0.01 vs. saline; P = NS cohort effect). Injection of rhGH attenuated subsequent GHRH-stimulated peak serum GH concentrations (micrograms per liter) to 7.8 +/- 1.9 (PP), 5.8 +/- 1.2 (MP), and 4.8 +/- 1.1 (YM) (each P < 0.01 vs. saline; P = NS pubertal effect). GH autofeedback reduced non-GHRH-stimulated (basal) serum GH concentrations by 0.74 +/- 0.28 (PP), 5.7 +/- 1.7 (MP) and 1.4 +/- 0.27 (YM) fold, compared with saline (P = 0.016 for MP vs. PP or YM). In addition to greater fractional autoinhibition, MP boys exhibited markedly accentuated postnadir escape (4.6-fold steeper slope) of suppressed GH concentrations (P < 0.001 vs. PP or YM). Linear regression analysis of data from all 18 subjects revealed that the fasting IGF-I concentration negatively predicted fold-autoinhibition of GHRH-stimulated peak GH release (r = -0.847, P = 0.006) and positively forecast fold-autoinhibition of basal GH release (r = +0.869, P < 0.001). In contrast, the kinetics of rhGH did not differ among the three study cohorts. In summary, boys in midpuberty manifest equivalent responsiveness to exogenous GHRH-stimulated GH secretion; heightened susceptibility to rhGH-induced fractional inhibition of endogenous secretagogue-driven GH release, compared with the prepubertal or adult male; and accelerated recovery of GH output after acute autonegative feedback. This novel tripartite mechanism could engender recurrent high-amplitude GH secretory bursts that mark sex hormone-dependent activation of the human somatotropic axis.

Pubertal alterations in growth and body composition. VI. Pubertal insulin resistance: relation to adiposity, body fat distribution and hormone release

OBJECTIVE

To investigate the independent influence of alterations in fat mass, body fat distribution and hormone release on pubertal increases in fasting serum insulin concentrations and on insulin resistance assessed by the homeostasis model (HOMA).

DESIGN AND SUBJECTS

Cross-sectional investigation of pre- (n=11, n=8), mid- (n=10, n=11), and late-pubertal (n=10, n=11) boys and girls with normal body weight and growth velocity.

MEASUREMENTS

Body composition (by a four-compartment model), abdominal fat distribution and mid-thigh interfascicular plus intermuscle (extramyocellular) fat (by magnetic resonance imaging), total body subcutaneous fat (by skinfolds), mean nocturnal growth hormone (GH) release and 06:00 h samples of serum insulin, sex steroids, leptin and insulin-like growth factor-I (IGF-I).

RESULTS

Pubertal insulin resistance was suggested by greater (P<0.001) fasting serum insulin concentrations in the late-pubertal than pre- and mid-pubertal groups while serum glucose concentrations were unchanged and greater (P<0.001) HOMA values in late-pubertal than pre- and mid-pubertal youth. From univariate correlation fat mass was most related to HOMA (r=0.59, P<0.001). Two hierarchical regression models were developed to predict HOMA. In one approach, subject differences in sex, pubertal maturation, height and weight were held constant by adding these variables as a block in the first step of the model (r(2)=0.36). Sequential addition of fat mass (FM) increased r(2) (r(2)((inc)remental)=0.08, r(2)=0.44, P<0.05) as did the subsequent addition of a block of fat distribution variables (extramyocellular fat, abdominal visceral fat, and sum of skinfolds; r(2)(inc)=0.11, r(2)=0.55, P<0.05). Sequential addition of a block of hormone variables (serum IGF-I and log((10)) leptin concentrations; r(2)(inc)=0.04, P>0.05) did not reliably improve r(2) beyond the physical characteristic and adiposity variables. In a second model, differences in sex and pubertal maturation were again held constant (r(2)=0.25), but body size differences were accounted for using percentage fat data. Sequential addition of percentage body fat (r(2)((inc)remental)=0.11, r(2)=0.36, P<0.05), then a block of fat distribution variables (percentage extramyocellular fat, percentage abdominal visceral fat, and percentage abdominal subcutaneous fat; r(2)(inc)=0.08, r(2)=0.44, P=0.058), and then a block of serum IGF-I and log((10)) leptin concentrations (r(2)(inc)=0.07, r(2)=0.51, P<0.05) increased r(2). Mean nocturnal GH release was not related to HOMA (r=-0.04, P=0.75) and therefore was not included in the hierarchical regression models.

CONCLUSION

Increases in insulin resistance at puberty were most related to FM. Accumulation of fat in the abdominal visceral, subcutaneous and muscular compartments may increase insulin resistance at puberty beyond that due to total body fat. Serum concentrations of leptin and IGF-I may further modulate HOMA beyond the effects of adiposity and fat distribution. However, the results are limited by the cross-sectional design and the use of HOMA rather than a criterion measure of insulin resistance.

Consequences of sport training during puberty

Growth at puberty depends on one's genetic potential, nutritional status and a series of hormones. Energy expenditure may modify the effects of these three factors on the linear growth rate and the relative proportions of fat-free and fat mass. Participation in sports where weight control is not required does not seem to affect pubertal timing or alter linear growth rate. The growth and maturation of athletes in weight control sports have the additional burden of energy output greater than intake; however, in only a minority the energy deficit is great enough to slow growth and maturation. Studies focusing on male wrestlers and female gymnasts are reviewed. In the wrestlers the hormonal picture is consistent with mild-to-moderate GH resistance and perhaps mild maturational delay, especially in the lower weight classes. The deficits in lean body mass and fat mass "catch-up" quickly following the end of training and competitive season. The situation with the gymnasts is somewhat different, the goal being to develop muscular strength within a shorter and lighter physique. Marked under-nutrition can keep these adolescents pre-pubertal for many years of training and competition. Whether subsequent growth is disproportionate or not remains indeterminate, but the marked delay in the onset of estrogen action can permanently cause the skeleton to be under-mineralized. In conclusion, most athletes continue to track along the centiles of their genetic potential. To define the mechanisms of growth and maturational delay one must longitudinally study children in weight-control sports.

The insulin-like growth factor system in kidney diseases

The insulin-like growth factor system is intimately involved in renal development, growth, function and the pathophysiology of several disease states. Exogenous IGF-I increases GFR and RPF, perhaps mediated by nitric oxide (NO). In chronic renal failure, IGF-I, the binding proteins and their fragments decrease bioavailability. After transplantation, the levels of bioactive IGF-I increase likely due to better nutrition and increased clearance of the binding proteins and their fragments. In the nephritic syndrome, a similar mechanism may be active, in that the binding proteins and their fragments may inhibit IGF-I action.

Alterations in body composition and fat distribution in growth hormone-deficient prepubertal children during growth hormone therapy

Growth hormone (GH) deficiency in children results in increased body fat, reduced fat-free mass (FFM) including muscle (protein) and bone, and abdominal obesity. Thus, proper GH secretion likely has major developmental influences on later health risks including cardiovascular diseases and osteoporosis. However, the in vivo control of the development of the body composition and fat distribution by GH has not yet been accurately investigated using children with GH deficiency as a model. We determined the effect of GH therapy (GH replacement, n = 3; GH + physiologic cortisol and thyroxine replacement, n = 3) on body composition, the proportional composition of the FFM, and body fat distribution in GH-deficient prepubertal children compared with healthy control children (n = 6) not treated with GH. The GH-deficient and control children were initially matched for gender, bone age, and weight. As assessed by a 4-compartment model, GH therapy reduced percent body fat during the first 3 months of therapy but not thereafter. This change was primarily due to FFM, which increased 3-fold more in the GH-deficient group and accounted for 91.5% of the increase in body weight. Fat mass increased in the controls but was unchanged in the GH-deficient group. Therapy temporarily increased the proportional contribution of water to the FFM, decreased the proportion of mineral, and slightly increased the proportion of protein. Using magnetic resonance imaging (MRI), abdominal visceral fat was reduced in the GH-deficient group and unchanged in the controls. Abdominal subcutaneous fat measured in the same image was not changed. The abdominal and suprailiac skinfold thicknesses also were not decreased in the GH-deficient group. In conclusion, within 1 to 3 months, GH therapy accelerates lean tissue accrual, especially the water and protein components, but has a smaller effect on reducing fat mass. GH therapy has site-specific effects on reducing abdominal adiposity.

Alterations in growth and body composition during puberty. IV. Energy intake estimated by the youth-adolescent food-frequency questionnaire: validation by the doubly labeled water method

BACKGROUND

Estimates of energy intake are required for an understanding of growth and disease; however, few methods of energy intake in children have been validated.

OBJECTIVE

Our objective was to validate energy intake estimated by the Youth-Adolescent Food-Frequency Questionnaire (YAQ) against the criterion total energy expenditure (TEE) by doubly labeled water (DLW).

DESIGN

Twenty-three boys and 27 girls (8.6-16.2 y of age) completed the YAQ and TEE measurements in 1 y.

RESULTS

Energy intake by the YAQ (10. 03 +/- 3.12 MJ) and energy expenditure by DLW (9.84 +/- 1.79 MJ) were similar (P: = 0.91) with large lower (-6.30 MJ) and upper (6.67 MJ) +/-2 SD limits of agreement. When within-subject CVs of repeated measures of the DLW and YAQ methods were used, 25 of the 50 subjects were deemed to have misreported their energy intake. The discrepancy in energy intake (YAQ - TEE) was related to body weight (r = -0.25, P: = 0.077) and percentage body fat (r = -0.24, P: = 0.09) but not to age (r = -0.07, P: = 0.63) or the time between measures. From logistic regression, fatter boys were more likely to underreport energy intake than were fatter girls.

CONCLUSION

The YAQ provides an accurate estimation of mean energy intake for a group but not for an individual.

Pubertal alterations in growth and body composition. V. Energy expenditure, adiposity, and fat distribution

We determined whether activity energy expenditure (AEE, from doubly labeled water and indirect calorimetry) or physical activity [7-day physical activity recall (PAR)] was more related to adiposity and the validity of PAR estimated total energy expenditure (TEE(PAR)) in prepubertal and pubertal boys (n = 14 and 15) and girls (n = 13 and 18). AEE, but not physical activity hours, was inversely related to fat mass (FM) after accounting for the fat-free mass, maturation, and age (partial r = -0.35, P < or = 0.01). From forward stepwise regression, pubertal maturation, AEE, and gender predicted FM (r(2) = 0.36). Abdominal visceral fat and subcutaneous fat were not related to AEE or activity hours after partial correlation with FM, maturation, and age. When assuming one metabolic equivalent (MET) equals 1 kcal. kg body wt(-1). h(-1), TEE(PAR) underestimated TEE from doubly labeled water (TEE bias) by 555 kcal/day +/- 2 SD limits of agreement of 913 kcal/day. The measured basal metabolic rate (BMR) was >1 kcal. kg body wt(-1). h(-1) and remained so until 16 yr of age. TEE bias was reduced when setting 1 MET equal to the measured (bias = 60 +/- 51 kcal/day) or predicted (bias = 53 +/- 50 kcal/day) BMR but was not consistent for an individual child (+/- 2 SD limits of agreement of 784 and 764 kcal/day, respectively) or across all maturation groups. After BMR was corrected, TEE bias remained greatest in the prepubertal girls. In conclusion, in children and adolescents, FM is more strongly related to AEE than activity time, and AEE, pubertal maturation, and gender explain 36% of the variance in FM. PAR should not be used to determine TEE of individual children and adolescents in a research setting but may have utility in large population-based pediatric studies, if an appropriate MET value is used to convert physical activity data to TEE data.

Adrenomedullary dysplasia and hypofunction in patients with classic 21-hydroxylase deficiency

BACKGROUND

Glucocorticoids are essential for the normal development and functioning of the adrenal medulla. Whether adrenomedullary structure and function are normal in patients with congenital adrenal hyperplasia is not known.

METHODS

We measured plasma and urinary catecholamines and plasma metanephrines in 38 children with congenital adrenal hyperplasia due to 21-hydroxylase deficiency (25 children with the salt-wasting form and 13 with the simple virilizing form), 39 age-matched normal subjects, and 20 patients who had undergone bilateral adrenalectomy. Adrenal specimens obtained from three other patients with 21-hydroxylase deficiency who had undergone bilateral adrenalectomy and specimens obtained at autopsy from eight other patients were examined histologically.

RESULTS

Plasma epinephrine and metanephrine concentrations and urinary epinephrine excretion were 40 to 80 percent lower in the patients with congenital adrenal hyperplasia than in the normal subjects (P<0.05), and the values were lowest in the patients with the most severe deficits in cortisol production. Urinary epinephrine excretion and plasma epinephrine concentrations were at or below the limit of detection of the assay in 8 (21 percent) of the patients with congenital adrenal hyperplasia and in 19 (95 percent) of the patients who had undergone adrenalectomy. In the group of patients with congenital adrenal hyperplasia, plasma epinephrine and metanephrine concentrations and urinary epinephrine excretion were approximately 50 percent lower in those who had been hospitalized for adrenal crises than in those who had not. In three patients with congenital adrenal hyperplasia who had undergone bilateral adrenalectomy, the formation of the adrenal medulla was incomplete, and electron-microscopical studies revealed a depletion of secretory vesicles in chromaffin cells.

CONCLUSIONS

Congenital adrenal hyperplasia compromises both the development and the functioning of the adrenomedullary system.

Growth hormone stimulation testing in both short and normal statured children: use of an immunofunctional assay

Accurate interpretation of the results of GH stimulation tests is of pivotal importance not only in the evaluation of the etiology of growth retardation in children but also in the selection of the best candidates for GH therapy. We performed this study to test a novel immunofunctional GH ( IFGH) assay that makes use of the concept that one GH molecule dimerizes two GH receptors and compared the results with those obtained using two GH assays, the Diagnostic Systems Laboratories ELISA and a Hybritech immunoradiometric assay in 19 children with short stature undergoing routine GH stimulation testing. We also tested 13 normally statured control children to revisit the issue of what constitutes normal GH responses to stimuli, using all three assays and arginine and either L-dopa or insulin-induced hypoglycemia as secretagogues. Concentrations of IGF-I, IGF binding protein-3, and acid labile subunit were measured as well. There was a significant correlation between peak IFGH and Diagnostic Systems Laboratories ELISA GH responses to stimuli (r(2) = 0.93) as well as between the Diagnostic Systems Laboratories ELISA and Hybritech immunoradiometric assay (r(2) = 0.91). There were no significant differences between the short stature and normal group in peak or mean GH concentrations regardless of the assay used; however, the IGF-I, IGF binding protein-3, and acid labile subunit concentrations were substantially lower in the short stature group. There was a wide spectrum of GH concentrations in the normal group; approximately 50% of the children had peak GH concentrations <7 ng/mL, approximately 30% <5 ng/mL, and two pubertal normal subjects peaked to only 2 ng/mL with use of both the ELISA and IFGH assays. We conclude that 1) sensitive GH assays, ELISA and immunoradiometric assay, accurately detect a GH capable of generating a biologic signal comparable to an IFGH and 2) that normal GH stimulation test results can be substantially lower than previously accepted. GH-dependent growth factors may be more sensitive indicators of GH sufficiency than GH concentrations in response to pharmacologic stimuli.

Longitudinal changes in growth hormone secretory process irregularity assessed transpubertally in healthy boys

Clarifying the time evolution, and underlying neuroendocrine regulation, of hormone secretion during puberty is of pivotal importance both physiologically and clinically. We sought to determine whether clinical growth and elevated growth hormone (GH) release in pubertal boys are associated with shifts in the irregularity of GH secretory patterns. We studied GH release in 23 healthy boys longitudinally at approximately 4-mo intervals over a 6-yr period throughout puberty, by repetitive blood sampling at 20-min intervals for 24 h on each study date. To quantify serial irregularity in the GH profiles, we utilized approximate entropy (ApEn), a scale- and model-independent quantification of the extent of sequential "randomness." Complementary statistical analyses establish that on a per-subject basis, serum GH concentration-time series show greatest secretory disorderliness (maximal ApEn) in prepuberty and mid-to-late puberty, followed by a steep decline in ApEn to maximal orderliness in postpubertal adolescence (P < 0.0001, ANOVA). Pooling all subject comparisons, we observed a persistent positive correlation between ApEn and growth velocity (GrVel), Pearson r = 0.467 (P < < 10(-10)). Moreover, in general, ApEn(GH) preceded GrVel evolution, with a time frame lead of 4-8 mo providing the most pronounced correlations between ApEn and GrVel. In the setting of low postpubertal growth, per-subject ApEn values fell to approximately one-half of maximal ApEn values and, on average, were in the 13th percentile from minimal (P < < 10(-10)) for fully mature boys. Thus, in a longitudinal transpubertal analysis, greater irregularity in GH secretion corresponds to greater linear growth in boys, which culminates in highly regular GH secretory dynamics after sexual maturity. In addition to clinical utility, there may be added experimental merit in knowing that GH dynamics typically predict accelerated linear growth in 4-8 mo.

Sex steroid and growth hormone supplementation to enhance performance in adolescent athletes

Ergogenic aids are taken to enhance energy utilization by producing more, controlling its use, or increasing mechanical efficiency. Most athletes are looking toward enhancing performance by proper training modalities and methods; however, some look to the biochemical route for a "quick fix." Thus, the use of chemical agents is on the rise. Herein is provided information on the anabolic-androgenic agents androstenedione, dehydroepiandrosterone, and the "parent" compound, testosterone. The former two, at best, have equivocal activity, but testosterone is both anabolic and androgenic in doses that adolescents might receive. Growth hormone and insulin-like growth factor-1 are anabolic, nonandrogenic compounds with undoubted effects on the lean body mass compartment. Both are expensive, not readily available, and subject to the art of counterfeiting. Thus, very few data are available in non-growth hormone-deficient adolescents. The discussion of these agents ends with issues of fairness, ethics, and the message we attempt to project to our teenagers, whether athletes or not.

Growth and pubertal development in children and adolescents: effects of diet and physical activity

The longitudinal growth of an individual child is a dynamic statement of the general health of that child. Measurements should be performed often and accurately to detect alterations from physiologic growth. Although any single point on the growth chart is not very informative, when several growth points are plotted over time, it should become apparent whether that individual's growth is average, a variant of the norm, or pathologic. Somatic growth and maturation are influenced by several factors that act independently or in concert to modify an individual's genetic growth potential. Linear growth within the first 2 y of life generally decelerates but then remains relatively constant throughout childhood until the onset of the pubertal growth spurt. Because of the wide variation among individuals in the timing of the pubertal growth spurt, there is a wide range of physiologic variations in normal growth. Nutritional status and heavy exercise training are only 2 of the major influences on the linear growth of children. In the United States, nutritional deficits result from self-induced restriction of energy intake. That single factor, added to the marked energy expenditure of training and competition for some sports, and in concert with the self-selection of certain body types, makes it difficult to identify the individual factors responsible for the slow linear growth of some adolescent athletes, for example, those who partake in gymnastics, dance, or wrestling.

Gender and sexual maturation-dependent contrasts in the neuroregulation of growth hormone secretion in prepubertal and late adolescent males and females--a general clinical research center-based study

Although numerous studies have delineated an impact of gender on the neuroendocrine control of GH secretion in the adult, few investigations have defined the nature and extent of sex differences before puberty. This deficit reflects jointly the sensitivity limitations of earlier GH assays and the paucity of intensive sampling protocols in healthy children. Here we have applied a chemiluminescence-based GH assay (sensitivity, 0.005 microg/L) to study GH release in blood sampled every 10 min for 12 h from 1800-0600 h in 58 healthy children. Males and females were evaluated in prepuberty (n = 17 boys; n = 11 girls) and late adolescence (n = 13 males; n = 17 females). We quantitated the principal regulated facets of GH release by 1) deconvolution analysis to assess basal vs. pulsatile GH secretion, 2) approximate entropy to compute the regularity of GH release patterns, and 3) cosine regression analysis to evaluate the overnight rhythmic release of GH. Gender by maturation analysis of variance revealed a mean 2.3-fold increase in the integrated serum GH concentration between prepuberty and late adolescence (P < 10(-6)). Deconvolution analysis disclosed that 91-97% of total GH secretion was pulsatile. Pulsatile, but not basal, GH release showed marked sexual maturation dependence (P < 10(-5)). Pulsatile GH release rose in adolescents due to a 2.25-fold greater GH secretory burst mass (P = 0.00011), which reflected joint 1.5-fold increases in GH secretory pulse amplitude and duration (P < 0.01). Pulse-mass enhancement across puberty was gender independent, but mechanistically specific, as GH pulse frequency, intersecretory burst interval, and half-life were invariant of pubertal status. The approximate entropy statistic identified more disorderly GH secretion patterns in adolescent females compared with prepubertal children and adolescent males (P = 0.00074). Cosinor analysis unmasked elevated overnight rhythms in GH secretory burst mass and interburst intervals in late adolescents of both genders compared with prepubertal boys (for burst mass) or girls (for interburst intervals). Linear regression analysis disclosed strong correlations among 1) the plasma insulin-like growth factor I concentration and GH secretory burst mass (P < 10(-3)), 2) the GH pulse mass and the serum testosterone concentration (P = 10(-3)), 3) the irregularity (entropy) of GH secretory patterns and the serum estradiol concentration (P < 10(-4)), and 4) the basal GH secretion rate and the serum estradiol concentration (P = 10(-2)). In summary, healthy prepubertal children and late adolescent boys and girls manifest distinctive mechanisms controlling GH release, as appraised for all three of the pulsatile, entropic, and 12-h rhythmic modes of GH neuroregulation. The major maturational contrast in the pulsatile mode of GH secretion is amplified secretory burst mass in adolescents due to jointly heightened GH pulse amplitude and duration. The dominant gender distinction lies in the reduced orderliness of GH release patterns in late adolescent girls. Overnight rhythms in GH secretory burst mass and interburst intervals enlarge in both sexes at adolescence, thus signaling enhanced coupling between the rhythmic and pulsatile control of GH release at this time. At the extrema of pubertal development, sex steroid hormones are associated differentially with specific facets of GH release, e.g. an elevated basal GH secretion rate (estrogen), greater irregularity of GH release patterns (estrogen), and amplified GH secretory burst mass and higher plasma insulin-like growth factor I concentrations (testosterone). Accordingly, we postulate that sex steroids supervise selectively each of the dominant facets of GH neurosecretory control across human puberty.

Spontaneous and GnRH-provoked gonadotropin secretion and testosterone response to human chorionic gonadotropin in adolescent boys with thalassaemia major and delayed puberty

To elucidate whether the cause of sexual maturation arrest in thalassaemia is of gonadal or pituitary etiology, 10 males with thalassaemia and delayed puberty and 10 with constitutional delay of growth and pubertal maturation (CSS) were extensively studied. Their spontaneous nocturnal gonadotropin secretion and gonadotropin response to intravenous 100 micrograms gonadotropin-releasing hormone (GnRH) were evaluated. Circulating testosterone concentration and clinical response were evaluated after 3 days, 4 weeks and 6 months of intramuscular administration of human chorionic gonadotropin (HCG) (2500 U/m2/dose). Thalassaemic boys had significantly lower circulating concentrations of testosterone compared to those with constitutional delay of growth and sexual maturation (CSS) at the same pubertal stage. Short- and long-term testosterone response to administrations of HCG was markedly decreased in thalassaemic boys. After 6 months of HCG administration 50 per cent (5/10) of the boys did not show significant testicular enlargement or genital changes. Despite the low circulating concentrations of testosterone, none of the patients had high basal or exaggerated gonadotropin response to gonadotropin releasing hormone (GnRH) stimulation. Luteinizing hormone (LH) peak responses to GnRH were significantly lower as compared to controls. Follicle-stimulating hormone (FSH) peak responses to GnRH did not differ among the two study groups. The mean nocturnal LH and FSH secretion was significantly decreased in all thalassaemic boys as compared to boys with CSS at the same pubertal stage (testicular volume). These data proved that hypogonadotropic hypogonadism is the main cause of delayed/failed puberty in adolescents with thalassaemia major. MRI studies revealed complete empty sella (n = 5), marked diminution of the pituitary size (n = 5), thinning of the pituitary stalk (n = 3) with its posterior displacement (n = 2), and evidence of iron deposition in the pituitary gland and midbrain (n = 8) in thalassaemic patients, denoting a high incidence of structural abnormalities (atrophy) of the pituitary gland. Moreover, in many of the thalassaemic boys, the defective testosterone response to long-term (6 months) HCG therapy denoted significant testicular atrophy and/or failure secondary to siderosis. It appears that testosterone replacement might be superior to HCG therapy in these patients. This therapy should be introduced at the proper time in these hypogonadal patients to induce their sexual development and to support their linear growth spurt and bone mineral accretion.

Role of leptin during childhood growth and development

Leptin, the product of the ob/ob gene in rodents, regulates energy balance and fertility. Two genetic models, the ob/ob mouse (deletion of leptin protein) and the db/db mouse (deletion of leptin receptor) have markedly augmented research in obesity. Human obesity is more closely linked to leptin resistance than to the absence of leptin. Serum leptin concentrations reflect the size of the subcutaneous fat depot better than total fat mass or abdominal visceral fat. At the initiation of puberty there is a divergence in circulating leptin concentrations between boys and girls. In boys, leptin concentrations increase and then markedly decrease to prepubertal concentration levels. In girls there are only increasing concentrations. The authors believe these patterns are relevant to the markedly different alterations in the regional distribution of body fat that occurs in boys and girls at puberty.

Spontaneous and provoked growth hormone (GH) secretion and insulin-like growth factor I (IGF-I) concentration in patients with beta thalassaemia and delayed growth

Growth retardation in children with thalassaemia major is multifactorial. We studied the growth hormone (GH) response to provocation by clonidine and glucagon, measured the circulating concentrations of insulin, insulin-like growth factor-I (IGF-I), IGF-binding protein-3 (IGFBP3), and ferritin, and evaluated the spontaneous nocturnal (12 h) GH secretion in prepubertal patients with thalassaemia and age-matched children with constitutional short stature (CSS) (height SDS < -2, but normal GH response to provocation). The anatomy of the hypothalamic pituitary area was studied in patients with abnormal GH secretion using MRI scanning. Children with thalassaemia had significantly lower peak GH response to provocation by clonidine and glucagon (8.8 +/- 2.3 micrograms/l and 8.2 +/- 3.1 micrograms/l respectively) than did controls (17.6 +/- 2.7 micrograms/l and 15.7 +/- 3.7 micrograms/l respectively). They had significantly decreased circulating concentrations of IGF-I and IGFBP3 (68.5 +/- 19 ng/ml and 1.22 +/- 0.27 mg/l respectively) compared to controls (153 +/- 42 ng/ml and 2.16 +/- 0.37 mg/l respectively). Seven of the thalassaemic children had a GH peak response of < 7 micrograms/l after provocation. Those with a normal GH response after provocation also had significantly lower IGF-I and IGFBP3 concentrations than controls. Analysis of their spontaneous nocturnal GH secretion revealed lower mean (2.9 +/- 1.77 micrograms/l) and integrated (2.53 +/- 1.6 micrograms/l) concentrations compared to controls (4.9 +/- 0.29 micrograms/l and 5.6 +/- 0.52 micrograms/l respectively). Five of them had mean nocturnal GH concentration < 2 micrograms/l and four had maximum nocturnal peak below 10 micrograms/l. These data denoted defective spontaneous GH secretion in some of these patients. MRI studies revealed complete empty sella (n = 2), marked diminution of the pituitary size (n = 4), thinning of the pituitary stalk (n = 3) with its posterior displacement (n = 2), and evidence of iron deposition in the pituitary gland and midbrain (n = 7) in those patients with defective GH secretion (n = 9). Serum ferritin concentration was correlated significantly with the circulating IGF-I (r = -0.47, p < 0.01) and IGFBP3 (r = -0.43, p < 0.01) concentrations. These data prove a high prevalence of defective GH secretion in thalassaemic children associated with structural abnormality of their pituitary gland.

Androgen replacement in children with constitutional delay of puberty: the case for aggressive therapy

Puberty describes the complex physiological transition between childhood and adulthood. Dramatic physical changes occur, most notably the development of secondary sexual characteristics and the pubertal growth spurt. During the adolescent growth spurt, growth velocity increases from pre-pubertal rates of 4-6 cm per year to as much as 10-15 cm per year. Accompanying the increase in gonadal steroids is an increase in amplitude of growth hormone secretory bursts. Evidence suggests that adequate growth hormone and gonadal steroids are both necessary for the attainment of a normal pubertal growth velocity, and the complex interplay between these two hormonal axes is under intense investigation. Delayed onset of puberty, or constitutional delay of growth and adolescence, is a common phenomenon presenting particularly in boys. Physiologically, it represents an extension of the normal pre-pubertal hypogonadotropic hypogonadal state. Without intervention, these children will spontaneously undergo puberty and often reach their genetic height potential, but their delay compared with that of their peers is often of concern to the children and their families. Recent evidence suggest long-term physiological benefits of early androgen replacement therapy in these boys, including maximizing attained bone mineral density. Androgen replacement therapy in male adolescents with constitutional delay of growth and adolescence is beneficial psychologically as well as physiologically and should be initiated promptly.

Gender differences in leptin levels during puberty are related to the subcutaneous fat depot and sex steroids

Little is known about the influence of adiposity and hormone release on leptin levels in children and adolescents. We utilized criterion methods to examine the relationships among sex steroids, body composition (4 compartment), abdominal visceral and subcutaneous fat (magnetic resonance imagery), total subcutaneous fat (sum of 9 skinfolds), energy expenditure (doubly labeled water), aerobic fitness, and serum leptin levels in prepubertal and pubertal boys (n = 16; n = 13) and girls (n = 12; n = 15). The sum of skinfolds accounted for more variance in leptin levels of all girls [coefficient of determination (R2) = 0.70, P < 0.001] and all boys (R2 = 0.60, P < 0.001) than the total fat mass (girls, R2 = 0.52, P < 0.001; boys, R2 = 0.23, P < 0.001). Total energy expenditure, corrected for the influence of fat-free mass, correlated inversely with leptin (R2 = 0.18, P = 0.02). Gender differences in leptin disappeared when corrected for sex steroid levels or the combination of adiposity and energy expenditure. In multiple regression, the sum of skinfolds and free testosterone and estrogen levels accounted for 74% of the variance in leptin levels. We conclude that serum leptin levels are positively related to subcutaneous adiposity but negatively related to androgen levels. Energy expenditure may be negatively related to leptin levels by reduction of the adiposity, or a common genetic factor may influence both the activity and serum leptin levels.

Repeated bouts of exercise alter the blood lactate-RPE relation

PURPOSE

To examine the effects of repeated bouts of exercise on the blood lactate [HLa]-ratings of perceived exertion (RPE) relation.

METHODS

Six moderately trained males were studied on two occasions: a sequential exercise bouts day (SEB: 1000 h, 1130 h, and 1300 h) and a delayed exercise bouts day (DEB: 1000 h, 1400 h, and 1800 h). Each of the three exercise bouts within a given condition were 30 min in duration at the power output (PO) associated with 70% of VO2peak on a cycle ergometer. A standardized meal was provided at 0600 h. VO2, PO, HR, and RER were recorded every min during exercise and blood [HLa] and RPE were measured every 5 min during exercise.

RESULTS

A 2 x 3 analysis of variance with repeated measures revealed that blood [HLa] decreased significantly with each repeated exercise bout (X +/- SEM: bout 1: SEB = 3.5 (0.3), DEB = 3.8 (0.4); bout 2: SEB = 2.6 (0.3), DEB = 2.8 (0.3); bout 3: SEB = 2.0 (0.2), DEB = 2.1 (0.4); mM). No differences were observed in the blood [HLa] response to repeated bouts of exercise between SEB and DEB. RPE-peripheral (legs, RPE-L) was higher during bout 3 compared with bout 1 (P <0.05) (bout 1: SEB = 11.8 (0.8), DEB = 12.3 (0.2); bout 2: SEB = 12.3 (0.5), DEB = 13.3 (0.4); bout 3: SEB = 13.5 (0.8), DEB = 14.0 (0.7); RPE-central (chest and breathing, RPE-C) was not affected by repeated bouts of exercise, whereas RPE-Overall (RPE-O) was higher during bout 3 compared with bouts 1 and 2 (P < 0.05) (bout 1: SEB = 12.5 (0.2), DEB = 12.3 (0.4); bout 2: SEB = 12.8 (0.4), DEB = 12.7 (0.4); bout 3: SEB = 13.7 (0.7), DEB = 13.2 (0.3)). No interaction for RPE x condition was observed. HR increased with repeated bouts of exercise with HR during exercise bout 3 being higher than HR during exercise bout 1 (164 vs. 156 bpm, P < 0.05). There was also a strong trend for HR during exercise bout 3 to be higher than HR during exercise bout 2 (P < 0.06). A trend for a reduction in VO2 with repeated exercise was observed (P < 0.07), with the reduction apparently related to the SEB condition (P < 0.12 for VO2 x condition). PO and kcal.min-1 were not affected by repeated bouts of exercise. RER decreased significantly with each repeated bout of exercise (from RER = 0.96 to RER = 0.89, P < 0.05) with no difference observed between SEB and DEB.

CONCLUSIONS

We conclude that the blood [HLa]-RPE relation is altered by repeated bouts of exercise and that this alteration does not appear to be affected by recovery time between exercise bouts (up to 3.5 h of recovery). These data suggest that, after the first exercise bout, RPE should not be used to produce a specific blood [HLa] on subsequent exercise bouts.

Discordant puberty in monozygotic twin sisters with neurofibromatosis type 1 (NF1)

Monozygotic twin sisters are reported who have discordant pubertal growth and sexual development. Although both sisters were physiologically appropriate for chronological age in their pubertal development, their adolescent development was considerably different from that expected of monozygotic twin sisters. The more pubertally advanced sister by magnetic resonance imaging had an optic pathway glioma while none was present in her twin sister. Precocious puberty is not an unexpected complication of neurofibromatosis type 1 and is always associated with the presence of an optic pathway glioma. These sisters emphasize the striking similarity that is expected of monozygotic twins and the need for investigation when intertwin differences in growth and/or development arise.

Alterations in growth and body composition during puberty: III. Influence of maturation, gender, body composition, fat distribution, aerobic fitness, and energy expenditure on nocturnal growth hormone release

We examined the relationships among gender, sexual maturation, four-compartment model estimates of body composition, body fat distribution (magnetic resonance imaging for abdominal visceral fat and anthropometrics), aerobic fitness, basal and total energy expenditure, and overnight GH release in an ultrasensitive chemiluminescence assay in healthy prepubertal and pubertal boys (n = 18 and 11, respectively) and girls (n = 12 and 18, respectively). Blood samples were withdrawn every 10 min from 1800-0600 h to determine the area under the serum GH-time curve (AUC), sum of the GH peak heights (sigma GH peak heights), and the mean nadir GH concentration. GH release was greater in the pubertal than prepubertal subjects due to an increase in sigma GH peak heights (43.8 +/- 3.6 vs. 24.1 +/- 3.5 ng.mL-1, P = 0.0002) and mean nadir (1.7 +/- 0.2 vs. 0.7 +/- 0.2 ng.mL-1, P = 0.0002), but not peak number (4.3 +/- 0.2 vs. 4.5 +/- 0.2). The girls had a greater sigma GH peak heights (39.0 +/- 3.5 vs. 28.8 +/- 3.6 ng.mL-1, P = 0.05) and mean nadir concentration (1.4 +/- 0.2 vs. 0.9 +/- 0.2 ng.mL-1, P = 0.05) than the boys. Significant inverse relationships existed between sigma GH peak heights (r = -0.35, P = 0.06) or mean nadir (r = -0.39, P = 0.04) and four-compartment percent body fat for all boys but not for all girls or when combining all subjects. For all girls, significant inverse relationships existed between sigma GH peak heights (r = -0.39, P = 0.03) or mean nadir (r = -0.37, P = 0.04) and waist/hip ratio. Similar inverse relationships in all boys or all subjects were not significant. Forward stepwise regression analysis determined that bone age (i.e. maturation, primary factor) and gender were the significant predictors of AUC, sigma GH peak heights, and mean nadir. The influence of maturation reflects rising sex steroid concentrations, and the gender differences appear to be because of differences in estradiol concentrations rather than to body composition or body fat distribution.

The effects of pubertal status and glycemic control on the growth hormone-IGF-I axis in boys with insulin-dependent diabetes mellitus

Dysregulation of the growth hormone (GH)-insulin-like growth factor-I (IGF-I) axis in children and adolescents with insulin-dependent diabetes mellitus (IDDM) is well documented. Elevated levels of circulating GH, increased GH secretory amplitude, and decreased concentrations of IGF-I, IGFBP-3, and GHBP have been related to poor glycemic control. We proposed that pubertal maturation may be a more significant factor, potentially overriding the effects of metabolic control, especially during mid-puberty when the GH-IGF-I axis is maximally stimulated. We studied 24 male children and adolescents with IDDM over a 5 year period. Subjects were grouped both by pubertal stage (prepubertal vs mid-pubertal) and by level of glycemic control (hemoglobin A1 (<9%, 9-11.5%, and >11.5%). Twenty-four hour every 20 minute blood sampling for GH determination was analyzed using the Cluster algorithm, and static measures of IGF-I, IGFBP-3, and GHBP were obtained. When analyzed by pubertal status, we found no difference in the number of GH secretory peaks or the interval between concentration peaks. The sum of the peak heights and area under the curve were significantly greater in the mid-pubertal boys, as was the average GH nadir. Serum levels of IGF-I and IGFBP-3 were greater in the mid-pubertal boys, but levels of GHBP were higher in the prepubertal boys. When analyzed by level of glycemic control, we found no differences in the number of GH secretory peaks or interval between peaks among the 3 groups. However, the sum of the peak heights, area under the curve, and average GH nadir were all lower in the group with the intermediate level of glycemic control (HgbA1 9-11.5%); no differences were observed between the other 2 groups. This relationship persisted when the mid-pubertal subjects were analyzed separately. No differences were found among the 3 groups for levels of IGF-I, IGFBP-3, or GHBP. We conclude that normal increases in GH secretion and levels of IGF-I and IGFBP-3 occur during mid-puberty in boys with IDDM. A concomitant increase in average GH nadir may reflect an underlying effect of metabolic control. Greater GH secretion was observed in the groups with the lowest and highest levels of glycemic control. We speculate that this may be related to an increased incidence of severe hypoglycemic episodes in the group with the lowest levels of glycosylated hemoglobin, resulting in metabolic derangements similar to those with elevated glycosylated hemoglobin levels.

Food availability affects neural estrogen receptor immunoreactivity in prepubertal mice

How underfeeding delays maturation of the central mechanisms affecting GnRH release at the onset of puberty, and why females are more sensitive to underfeeding than males are not well understood. We tested the hypothesis that the sexually dimorphic effects of underfeeding on GnRH release are mediated in part through the estrogen receptor (ER). We investigated the influence of underfeeding on the number of ER-immunoreactive (ER-ir) cells in the medial preoptic area (mPOA), ventromedial nucleus (VMN), and arcuate nucleus (ARH) of prepubertal CF-1 mice, neural areas known to influence GnRH release. In females, 7 days of underfeeding reduced detectable ER-ir cells in the mPOA and VMN, but not in the ARH. Also, we noted a direct relationship between the percent body weight change the last 24 h before perfusion and the numbers of ER-ir cells in the mPOA (r = 0.69; P = 0.0008) and VMN (r = 0.56; P = 0.01). In males, 17 days of underfeeding did not affect ER-ir cell numbers in any region. A subsequent investigation of the time course of alterations in ER immunoreactivity revealed that in female mice ER-ir cell numbers were reduced within 48 h of underfeeding in the mPOA, VMN, and ARH. ER-ir cell number was not changed in male mice. When female mice were underfed for 48 h and then refed, ER-ir cell numbers normalized by 24 h in the mPOA, VMN, and ARH. For the time-course experiments, the percent body weight change the last 24 h before perfusion and the number of ER-ir cells were related in the mPOA (r = 0.47; P < 0.001) and VMN (r = 0.49; P < 0.001), but not in the the ARH (r = 0.23; P < 0.12) in female mice, and in the mPOA (r = 0.66; P < 0.001), VMN (r = 0.33; P = 0.06), and ARH (r = 0.45; P = 0.007) in male mice. Thus, despite no significant change in ER-ir cell number in the male mice, there was a relationship between the percent body weight change during the last 24 h before perfusion and the number of ER-ir cells. We conclude that in male mice, correlation analyses between the percent body weight change before perfusion and ER-ir cell number may be a more sensitive marker of the metabolic condition at the time of perfusion. In female mice, underfeeding may stall puberty by reducing the number of ER-ir cells in brain areas important for signal transmission of GnRH release.

Human growth hormone response to repeated bouts of aerobic exercise

We examined whether repeated bouts of exercise could override growth hormone (GH) auto-negative feedback. Seven moderately trained men were studied on three occasions: a control day (C), a sequential exercise day (SEB; at 1000, 1130, and 1300), and a delayed exercise day (DEB; at 1000, 1400, and 1800). The duration of each exercise bout was 30 min at 70% maximal O2 consumption (VO2max) on a cycle ergometer. Standard meals were provided at 0600 and 2200. GH was measured every 5-10 min for 24 h (0800-0800). Daytime (0800-2200) integrated GH concentrations were approximately 150-160% greater during SEB and DEB than during C: 1,282 +/- 345, 3,192 +/- 669, and 3,389 +/- 991 min.microgram.l-1 for C, SEB, and DEB, respectively [SEB > C (P < 0.06), DEB > C (P < 0.03)]. There were no differences in GH release during sleep (2300-0700). Deconvolution analysis revealed that the increase in 14-h integrated GH concentration on DEB was accounted for by an increase in the mass of GH secreted per pulse (per liter of distribution volume, lv): 7.0 +/- 2.9 and 15.9 +/- 2.6 micrograms/lv for C and DEB, respectively (P < 0.01). Comparison of 1.5-h integrated GH concentrations on the SEB and DEB days (30 min exercise + 60 min recovery) revealed that, with each subsequent exercise bout, GH release apparently increased progressively, with a slightly greater increase on the DEB day [SEB vs. DEB: 497 +/- 162 vs. 407 +/- 166 (bout 1), 566 +/- 152 vs. 854 +/- 184 (bout 2), and 633 +/- 149 vs. 1,030 +/- 352 min.microgram.l-1 (bout 3), P < 0.05]. We conclude that the GH response to acute aerobic exercise is augmented with repeated bouts of exercise.

Estrogen and testosterone, but not a nonaromatizable androgen, direct network integration of the hypothalamo-somatotrope (growth hormone)-insulin-like growth factor I axis in the human: evidence from pubertal pathophysiology and sex-steroid hormone replacement

Activation of the gonadotropic and somatotropic axes in puberty is marked by striking amplification of pulsatile neurohormone secretion. In addition, each axis, as a whole, constitutes a regulated network whose feedback relationships are likely to manifest important changes at the time of puberty. Here, we use the regularity statistic, approximate entropy (ApEn), to assess feedback activity within the somatotropic (hypothalamo-pituitary/GH-insulin-like growth factor I) axis indirectly. To this end, we studied pubertal boys and prepubertal girls or boys with sex-steroid hormone deficiency treated short-term with estrogen, testosterone, or a nonaromatizable androgen in a total of 3 paradigms. First, our cross-sectional analysis of 53 boys at various stages of puberty or young adulthood revealed that mean ApEn, taken as a measure of feedback complexity, of 24-h serum GH concentration profiles is maximal in pre- and mid-late puberty, followed by a significant decline in postpubertal adolescence and young adulthood (P = 0.0008 by ANOVA). This indicates that marked disorderliness of the GH release process occurs in mid-late puberty at or near the time of peak growth velocity, with a return to maximal orderliness thereafter at reproductive maturity. Second, oral administration of ethinyl estradiol for 5 weeks to 7 prepubertal girls with Turner's syndrome also augmented ApEn significantly (P = 0.018), thus showing that estrogen per se can induce greater irregularity of GH secretion. Third, in 5 boys with constitutionally delayed puberty, im testosterone administration also significantly increased ApEn of 24-h GH time series (P = 0.0045). In counterpoint, 5 alpha-dihydrotestosterone, a nonaromatizable androgen, failed to produce a significant ApEn increase (P > 0.43). We conclude from these three distinct experimental contexts that aromatization of testosterone to estrogen in boys, or estrogen itself in girls, is likely the proximate sex-steroid stimulus amplifying secretory activity of the GH axis in puberty. In addition, based on inferences derived from mathematical models that mechanistically link increased disorderliness (higher ApEn) to network changes, we suggest that sex-steroid hormones in normal puberty modulate feedback within, and hence network function of, the hypothalamo-pituitary/GH-insulin-like growth factor I axis.

Alterations in growth and body composition during puberty. I. Comparing multicompartment body composition models

A four-compartment (4C) model of body composition was used as a criterion to determine the accuracy of three-compartment (3C) and two-compartment (2C) models to estimate percent body fat (%BF) in prepubertal and pubertal boys (genital I & II, n = 17; genital III & IV, n = 7) and girls (breast I & II, n = 8; breast III & IV, n = 15). The 3C water-density (3C-H2O) and 3C mineral-density models, dual-energy X-ray absorptiometry, the Lohman age-adjusted equations, the Slaughter et al. skinfold equations, and the Houtkooper et al. and Boileau bioelectrical impedance equations were evaluated. Agreement with the 4C model increased with the number of compartments (i.e., body water, bone mineral) measured. Except for the 3C-H2O model, the limits of agreement were large and did not perform well for individuals. The mean %BF by dual-energy X-ray absorptiometry (23.6%) was greater than that of the criterion 4C method (21.7%). For the field methods, the Slaughter et al. skinfold equations performed better than did the Houtkooper et al. and Boileau bioimpedance equations. The hydration of the fat-free mass decreased (genital I & II = 75.7%, genital III & IV = 74.8%, breast I & II = 75.5%, breast III & IV = 74.4%) and the mineral content increased (genital I & II = 4.9%, genital III & IV = 5.0%, breast I & II = 5.1%, breast III & IV = 5.7%) with maturation. The density of the fat-free mass also increased (genital I & II = 1.084 g/ml, genital III & IV = 1.087 g/ml, breast I & II = 1.086 g/ml, breast III & IV = 1.091 g/ml) with maturation. All of the models reduced the %BF overprediction of the Siri 2C model, but only the 4C and 3C-H2O models should be used as criterion methods for body composition validation in children and adolescents.

Comparison of pulsatile luteinizing hormone secretion between prepubertal children and young adults: evidence for a mass/amplitude-dependent difference without gender or day/night contrasts

The assessment of pulsatile GnRH activity in children has become possible since the introduction of the sensitive third generation immunochemiluminescent assays, permitting detection of previously unmeasurable levels of LH and FSH. Despite this, however, studies differ with regard to pulse frequency and the presence of a diurnal variation in LH secretion in clinically prepubertal children. Discrepancies may reflect the limitations of relatively long intersampling intervals, less sensitive LH assays such as RIAs, and the use of algorithms to analyze pulsatile LH secretion, which do not account for endogenous production rates and metabolic clearance. To address this, we studied LH secretion in 10 prepubertal children (4 boys and 6 girls, age 8.5-10.8 y) and 12 young adults (7 men and 5 women in the early follicular phase, age 18.6-32.8 y). Blood was sampled every 5 min from 2000 h to 0200 h (nighttime) and from 0800 h to 1400 h (daytime) for LH determination, using an immunochemiluminescent assay. Deconvolution analysis revealed no difference between daytime and nighttime LH secretion, including LH secretory amplitude and pulse frequency, within any of the 4 groups, permitting pooling of the data from the 2 sampling intervals for analysis. In addition, there was no difference in LH secretion or half-life between genders. Comparison of pulsatile LH secretion between children and adults revealed a marked increase in the mass and amplitude of LH secreted per burst. LH secretory burst mass rose 9.5-fold in females, increasing the mean LH concentration by nearly 13-fold and the production rate by nearly 9-fold. The trend in males was similar although less remarkable, with a 4.2-fold rise in LH secretory burst mass from childhood to adulthood. No differences in pulse frequency, interburst interval, half-life, or approximate entropy were found between prepubertal children and adults. We conclude that the maturational change in LH secretion occurs via a highly specific mass/amplitude-dependent mechanism without significant gender or day/night differences.

Exercise and growth hormone: does one affect the other?

The release of growth hormone (GH) is sensitive to many pharmacologic and physiologic stimuli, including exercise. Although the role of the increased amount of GH released during exercise is not fully understood, it most likely contributes to metabolic fuel adaptations during exercise, and tissue repair after the exercise session. The GH response to exercise is altered by many factors, including sex steroid concentrations, fitness level, and the intensity of previous exercise sessions. For both endurance and resistance exercise, greater activation of anaerobic glycolysis and lactate formation increases the amount of GH released. Whether an endurance exercise session or an endurance exercise training regimen influences the total amount of GH released during a 24-hour period is not clear; this may depend on the gender of the person, the intensity of the exercise, and the duration of exercise training. The influence of a single session of resistance exercise or resistance training on 24-hour GH secretion has not been studied. Preexercise diet modulation (especially modulation of fat intake) may also influence the release of GH during endurance exercise. Studies that measure the 12- to 24-hour GH response to resistance exercise after the ingestion of various macronutrient diets have not been completed.

A longitudinal assessment of hormonal and physical alterations during normal puberty in boys. V. Rising leptin levels may signal the onset of puberty

Leptin, the product of the ob gene, is an adipocyte-derived hormone that signals the amount of adipose tissue energy stores to the brain and exerts major effects on energy homeostasis and neuroendocrine function. Leptin has recently been shown to affect reproductive function in leptin-deficient and normal rodents. As puberty, the process of sexual maturation and acquisition of reproductive competence, has been proposed to be triggered by the attainment of a critical amount and/or distribution of fat, we examined whether changes in circulating leptin levels could represent the hormonal signal responsible for triggering the onset of puberty in humans. Eight prepubertal boys (Tanner genital stage 1 or early stage 2 at the initiation of the study) were evaluated longitudinally for 2.5-5.1 yr depending on when Tanner stage 5 of genital development was achieved. Sera for the determination of leptin, testosterone, and dehydroepiandrosterone sulfate were obtained every 4 months during the period of the study. Compared to baseline prepubertal levels (8 months before the onset of puberty, as defined by the initial rise in testosterone above the detection limit of the assay), leptin levels rose by approximately 50% just before the onset of puberty and decreased to approximately baseline values after the initiation of puberty (P < 0.01, by ANOVA), remaining stable for more than 2 yr. These changes occurred despite constantly increasing body mass index (P < 0.05, by ANOVA). No significant association between leptin and dehydroepiandrosterone sulfate concentrations was detected. In conclusion, the levels of circulating leptin are consistent with the hypothesis that this molecule is an important signal responsible for triggering the onset of puberty. The stimulus for a surge in leptin levels just before the onset of puberty is currently unknown.

Maturation of the regulation of growth hormone secretion in young males with hypogonadotropic hypogonadism pharmacologically exposed to progressive increments in serum testosterone

To study the onset of the action of gonadal sex steroids on the GH axis in spontaneous puberty, which is prolonged and sparingly predictable, we present a clinical investigative paradigm in which six previously untreated boys with isolated hypogonadotropic hypogonadism were exposed to progressively higher testosterone levels designed to mimic the androgen environment recognized during the early stages of puberty. We administered three incremental doses of testosterone (25-, 50-, and 100-mg im injections), each over a period of 4 weeks. Studies of overnight pulsatile GH secretion and GH responses to GHRH alone or combined with L-arginine (a functional somatostatin antagonist) were performed before testosterone administration and after each dose of testosterone. Serum testosterone, but not estrogen, levels increased progressively in all subjects during therapy. Deconvolution analysis of GH release profiles disclosed that GH secretory burst mass was stimulated significantly even by 25 mg testosterone. This parameter was not altered further by higher doses of testosterone. Spontaneous GH secretory burst number and amplitude increased significantly only after the 50- and 100-mg testosterone treatments, after which the serum GH response to GHRH and arginine also rose significantly. In contrast, the GH response to GHRH alone was not significantly affected by any dose of testosterone. Serum testosterone levels correlated significantly with the primary parameters of nocturnal GH secretion. In summary, our experimental model suggests that in males even very small increases in circulating testosterone occurring during the earliest stages of puberty are able to amplify pulsatile GH secretion. Our concomitant secretagogue data further suggest that testosterone exerts its action at different sites in the hypothalamo-somatotropic axis, i.e. directly at the pituitary level, and also at hypothalamic loci, possibly increasing both GHRH and somatostatin release.

The short-term infusion of ovine corticotropin-releasing hormone does not alter luteinizing hormone concentrations in young adult men

Chronic stress leads to suppression of the hypothalamic-pituitary-gonadal (HPG) axis with decreased plasma LH concentrations. This is believed to be due to the influence of elevated levels of endogenous CRH mediated via the endogenous opiate peptide receptor. Efforts to reproduce this phenomenon with exogenous CRH have produced varied results depending on the dose and route of administration of CRH as well as on the species, gonadal state, and endogenous opiate peptide system tone of the experimental subjects. In humans, conflicting results for CRH-induced suppression of the HPG axis exist for women, and the issue has not been addressed sufficiently in men. We, therefore, studied the effects of a 4-h infusion of ovine CRH (oCRH) on LH secretion in 11 healthy, nonobese young adult men (age range, 20-33 yr). Subjects were admitted to the General Clinical Research Center on 4 occasions in randomized order. They underwent blood sampling for LH at 10-min intervals from 1800-0600 h. From 2200-0200 h, subjects received one of the following iv infusion protocols in blinded fashion: a normal saline (NS) bolus and NS infusion, a naloxone (NAL) bolus (4 mg) and NAL infusion (2 mg/h), a NS bolus and oCRH infusion (1 microgram/kg.h; maximum, 75 micrograms/h), and a NAL bolus and both NAL and oCRH infusions, using the above-mentioned doses. For each time point, serum LH values from the four experimental conditions were compared by one-way ANOVA with repeated measures; the paired t test was applied post-hoc. This experimental model is predicted to have a beta-error of less than 0.10 for identifying a 1.0 U/L change in LH levels. As expected, NAL was associated with a transient, but significant, rise in serum LH concentrations compared to those in the NS control. On the other hand, oCRH administration did not result in any significant alteration in either basal or NAL-stimulated LH levels. We conclude that exogenous oCRH administration does not significantly alter pituitary secretion of LH in healthy men. We speculate that any suppressive effect of CRH on the HPG axis occurs at the level of the hypothalamus.

Serum lipid levels and steroidal hormones in women runners with irregular menses

This study compared the lipid profile of women runners with menstrual cycle irregularities with their normally menstruating counterparts. Relationships among selected steroid hormones and serum lipid levels in 10 eumenorrheic (EU) and 8 oligo-/amenorrheic (O/A) women runners and 6 eumenorrheic controls (CON) were examined. Serum 17 beta-estradiol (E2), progesterone (Prog), and dehydroepiandrosterone-sulfate (DHEAS) concentrations were determined in daily blood samples for 21 days, and integrated concentrations were calculated. Fasting blood samples were analyzed for total cholesterol (TC), low-density lipoprotein cholesterol (LDL-C), high-density lipoprotein cholesterol (HDL-C), HDL2, HDL3, triglycerides (Trig), and apolipoproteins A-1, A-II, and B. The O/A group had significantly lower E2 and Prog than EU or CON groups. Women in the CON group had lower HDL-C and HDL3 than the runners. With all women grouped together, E2 was not significantly correlated with any measured blood lipid parameters. On the other hand, DHEAS was significantly correlated with HDL-C, HDL2, and apolipoprotein A-I. These data demonstrate that women runners, regardless of menstrual cycle status, exhibit higher HDL-C concentrations than CON and supports previous research reporting a positive association between DHEAS and HDL-C.

A longitudinal assessment of hormonal and physical alterations during normal puberty in boys. III. The neuroendocrine growth hormone axis during late prepuberty

Cross-sectional studies demonstrating that physiological GH secretion varies widely among normally and slowly growing children as well as adults have created uncertainty over the definition of normal GH secretion. Furthermore, recent data indicate that the pattern of GH released under identical physiological conditions may be unique for each individual, and suggest that normality may be an individually defined condition. To investigate and develop further this concept and to avoid the confounding effects of fluctuating gonadal steroid hormone levels, we chose as a model normally growing prepubertal boys and performed a longitudinal assessment of spontaneous GH release characteristics (36 24-h GH secretion studies in 9 boys over 9-19 months). Assessment of serum GH pulse characteristics was accomplished using the Cluster pulse detection algorithm. Characteristics of underlying pituitary GH secretory events were estimated by multiple parameter deconvolution analysis. Approximate entropy was used to quantify the serial regularity or orderliness of GH release over 24 h. Among the group data, mean 24-h GH concentrations spanned a range of more than 4-fold (1.6-7.0 micrograms/L). The intersubject coefficient of variation (CV) was 41%. In contrast, values from individuals exhibited much less variability, not only for mean 24-h GH level (CV = 25 +/- 4%; P = < 0.02), but also for all assessed component GH pulse properties (P < 0.01) vs. intersubject values). Similarly, the estimated daily GH production rate, the calculated GH half-lives, and all parameters of GH secretory events varied much less for intraindividual compared to interindividual values. The sizes of the serum GH pulses gave rise to the greatest differences in overall serum GH level among individuals, as demonstrated by the large within-subject CV (50%). The most constant pulse characteristic among subjects was that of 24-h GH pulse frequency (intersubject CV = 30%). Approximate entropy estimates disclosed high within-subject consistency (mean CV = 15%). Several aspects of GH secretion and serum concentrations varied inversely with the subject's mean age-adjusted body mass index, including the 24-h GH production rate (r = -0.67; P < 0.05), the GH secretory burst amplitude (r = -0.73; P = 0.026), the mean serum GH pulse amplitude (r = -0.79; P = 0.011), and the sum of the GH pulse amplitudes (r = -0.66; P = 0.05). By contrast, no consistent pattern of increase or decrease in serum GH concentrations with advancing age was detectable during the prepubertal period. These data suggest that during prepuberty, 1) individual boys regulate daily GH secretion within relatively confined limits characteristic for that individual, much narrower than the range present in the larger population; 2) differences in mean 24-h GH levels among normally growing prepubertal boys arise primarily from differences in GH pulse size; 3) differences in body composition, as indicated by the body mass index, may influence the GH secretion range characteristic of each individual; and 4) there is no consistent change in mean 24-h GH concentrations or the orderliness (approximate entropy) of the GH release process ever time during late prepuberty as the onset of puberty approaches.

Management of puberty in growth hormone deficient children

At puberty there occur marked increases in gonadotropin, gonadal steroid and GH secretion. An important physiological synergism exists between the gonadal and somatotropic axes to permit the growth spurt and adolescent development; however, epiphyseal maturation is also accelerated leading to cessation of long-bone growth. GH deficiency may be absolute, but often is not and the diagnosis may be complicated by a constellation of physical and hormonal findings that are along a spectrum from low normal GH sufficiency to absent GH secretion. Growth hormone therapy not only accelerates the growth velocity, but also promotes the redistribution of adipose tissue stores to more peripheral sites. Given the remarkable physiological alterations in the activities of the GH and gonadotropin gonadal axes during adolescence in normal children, how should the therapeutic plan for the treatment of prepubertal GH deficiency be altered at puberty? Evidence for efficacy has been reported for each of the following for the treatment of GH deficiency at adolescence: 1) GH alone at the usual dosage (approximately 0.3 mg.kg-1.day-1); 2) Double or triple the amount of GH to mimic the finding of increased GH release at puberty. 3) GH at the usual or moderately increased dose and gonadotropin releasing hormone agonist analog to halt pubertal development. The latter two plans are at present hypotheses that must withstand the rigor of proper controlled trials. The end point is more than merely adult height, because of the significant psychological and skeletal system dysregulation that accompany decrements in the gonadal steroid hormones during adolescence.