Low urinary GH levels in normal statured obese children

An investigation of fetal, postnatal and childhood growth with insulin-like growth factor I and binding protein 3 in adulthood

OBJECTIVE

Weight at birth and adult height are positively associated with cancer risk. These patterns may be mediated by the insulin-like growth factor (IGF) axis. We have examined whether pre- and postnatal growth patterns have a long-term influence on adult IGF-I and IGFBP-3 levels.

DESIGN

A follow-up study of a randomized controlled trial of milk supplementation in pregnancy and childhood.

SUBJECTS

A total of 951 individuals took part in a study of diet and growth in South Wales between 1972 and 1974 followed up from birth until their mid-20s.

MEASUREMENTS

Anthopometric measures at birth, postnatally up to 5 years of age and in adulthood, and serum measures of IGF-I and IGF-I to IGFBP-3 ratio at mean age of 25 years.

RESULTS

A total of 63 subjects (70%) provided blood for analysis. We found no association between birth dimensions and adult IGF-I. Subjects who exhibited 'catch-down growth' had lower IGF-I levels (P-value for trend 0.02). Adult height was positively related to IGF-I, for every one standard deviation increase in adult height, IGF-I increased by 3.75 ng/dl (95% CI 0.46-7.08, P = 0.03). Adiposity was inversely associated with the IGF-I and IGF-I to IGFBP-3 ratio and positively associated with IGFBP-3. The strength of the associations increased with age. Downward centile crossing at any time in childhood was associated with lower IGF-I whilst the highest levels were observed in subjects who were tall throughout their early life course. Adult height remained a significant predictor of IGF-I even after adjustment for earlier growth.

CONCLUSIONS

Our results indicate that IGF-I levels in early adulthood are associated with patterns of childhood growth as well as adult stature and adiposity. These associations suggest the IGFs may contribute to anthropometric associations with cancer risk.

Plasma and urinary GH following a standardized exercise protocol to assess GH production in short children

Plasma and urinary GH responses following acute physical exercise were evaluated in 19 short-statured children (12 males, 7 females, median age: 11.4 yr, age range: 6.1-14.5 yr, Tanner stage I-III, height < or = 3rd centile for age; 7 with familial short stature, FSS; 8 with constitutional growth delay, CGD; 4 with GH deficiency, GHD) and 7 normally growing, age- and sex-matched control children (4 males, 3 females, median age 11.0 yr, range: 7.2-13.1 yr, Tanner stage I-III). All patients and controls underwent a standardized exercise protocol (consisting of jogging up and down a corridor for 15 min, strongly encouraged to produce the maximum possible effort, corresponding to 70-80% of the maximal heart rate) after an overnight fasting. Samples for plasma GH determinations were drawn at 0 time (baseline), at 20 min (5 min after the end of exercise) and at 35 min (after 20 min of rest); urine samples were collected before (0 time) and at 40, 80 and 120 min after exercise. The distance covered by children with GHD during the test was significantly lower (p<0.05) than in the other groups of patients and controls. No differences in the pattern of plasma GH responses after physical exercise were found between children with FSS, CGD and healthy controls, the maximum percent increase (vs baseline) being evident at 20 min (median, FSS: +1125%; CGD: +1271%; controls: +571%). Children with GHD showed a smaller percent increase (+94%) of plasma GH, significantly lower (p<0.01) than those recorded in the other groups. A significant percent increase (p<0.01) of baseline urinary GH following exercise was found in children with FSS (median: +34%), CGD (+18%) and controls (+44%). Children with FSS and CGD showed a gradual increase of urinary GH, reaching the maximum at 80 min, while healthy controls had a more evident and precocious increase (maximum at 40 min). Urinary median GH levels did not change following physical exercise in children with GHD (-5%, not significant). A significant correlation was found between the maximal percent increase (vs baseline) of plasma and urinary GH following physical exercise (r=0.7, p<0.001). In conclusion, our results show that: 1) plasma and urinary GH responses (as well as the distance covered and the number of steps, i.e. the physical performance) to a standardized exercise protocol are similar in children with FSS, CGD and in normal-statured controls, being unable to differentiate among the "normal variants" of growth; 2) children with GHD, unable to accomplish the same performance of the other three groups, show significantly reduced plasma and urinary GH responses following physical exercise. Although the determination of GH responses to pharmacological stimuli remains the definitive tool for the diagnosis of GHD, these preliminary results seem to suggest a potential role of urinary (and plasma) GH response to a standardized exercise protocol as a safe, acceptable first screening test for GH sufficiency also in children, as previously reported in adults.

Programming other hormones that affect insulin

The metabolic syndrome is associated with a marked increase in risk of type 2 diabetes and atherosclerotic vascular disease (AVD). The mechanism responsible for the metabolic syndrome is uncertain, but recent evidence suggests that a combination of low birth weight and adult obesity is associated with a markedly increased prevalence. Insulin resistance is the cardinal feature of the metabolic syndrome. Several hormones, have modes of action that either potentiate or reduce the biological actions of insulin and, therefore, attenuate or induce insulin resistance. Since insulin action may be modified, these hormones potentially contribute to the pathogenesis of the metabolic syndrome. The purpose of this review is to discuss programming of hormones that modulate insulin action. The review focuses on two major endocrine pathways: (i) glucocorticoid hormone action; and (ii) the growth hormone (GH)-insulin-like growth factor (IGF-1) axis, and discusses mechanisms linking abnormal activity of these pathways with reduced early growth, adult obesity and the metabolic syndrome.

The impact of gender, puberty and body mass on reference values for urinary growth hormone (GH) excretion in normally growing non-obese and obese children

OBJECTIVE

There is a lack of normal reference data on urinary GH (u-GH) excretion in children. We have investigated the impact of age, gender, pubertal development and body mass on reference values for u-GH excretion in normally growing non-obese and obese children.

STUDY DESIGN

u-GH levels were evaluated in 1153 healthy normal children (aged 5-14) and in 684 obese children (body mass index, BMI: > 75th). u-GH levels (ng/8 h) were determined by ELISA as the mean value of three consecutive first morning voidings.

RESULTS

Reference values (5-95th centile) for u-GH excretion in obese and non-obese children of both sexes are reported. In normal prepubertal children median u-GH levels were relatively stable and superimposable in the two sexes; subsequently, u-GH levels increased, reaching a peak value at 13 years in both sexes. Significant increments (P < 0.0001) in u-GH levels were shown at B2 for females and at G3 for males. A slight decline was evident at 14 years. In obese children, median u-GH concentrations were significantly lower than those recorded in normal children of prepubertal age and at all stages of puberty (except in females at B2), in spite of their comparable normal height. u-GH levels significantly increased at puberty also in obese children, although the pubertal rise was significantly (P < 0.001) lower (1.7-fold in both sexes) than that observed in normal children (2.5-fold in boys and 2.3-fold in girls). A multiple regression analysis showed that both chronological age (beta: 0.20), BMI (beta: - 0.11), gender (beta: - 0.04) and pubertal stage (beta: 0.25) contributed significantly to the physiological variation in u-GH levels (multiple R: 0.44, P < 0.00001).

CONCLUSIONS

This study provides reference values for u-GH in normally growing non-obese and obese children, analysing the impact of gender, puberty and body mass on this parameter. In agreement with previous studies, which demonstrate blunted GH-responses to provocative stimuli and reduced nocturnal GH concentration, obese children have significantly lower u-GH levels than age-matched normal weight children, both before and during puberty.

Reduced foetal growth and growth hormone secretion in adult life

OBJECTIVES

Recent studies suggest that growth restriction or other adverse influences acting in utero or during early infancy lead to permanent alterations in growth hormone (GH) secretion. As GH secretion is known to predict cardiovascular risk, alterations in GH may contribute to the association between reduced foetal growth and cardiovascular disease. We have therefore assessed the relationship between birth size and GH secretion in a prospective study of young adults whose birth size was recorded and who have had their current blood pressure and glucose tolerance measured.

DESIGN

Prospective cohort study

PATIENTS

153 healthy men and women, aged 20-21 years.

MEASUREMENTS

Subjects carried out a timed overnight urinary collection for analysis of GH excretion. Insulin sensitivity and insulin secretion were measured using the intravenous glucose tolerance test with minimal model analysis. Blood pressure, height, weight, usual level of exercise, smoking habits, alcohol consumption, and socio-economic status were also recorded.

RESULTS

GH excretion ranged from 0.01 to 41.8 microU per subject. It did not differ according to gender but was markedly reduced in obese subjects (P < 0.0001) Low birthweight was strongly associated with low GH excretion at age 20 years (P = 0.002). Low placental weight and short body length also predicted low GH (P = 0.02 and P = 0.04, respectively). These relationships were independent of other confounding factors including obesity. GH excretion was not independently related to current levels of blood pressure, insulin sensitivity or insulin secretion.

CONCLUSIONS

Body size at birth predicts GH excretion in adult life. Low GH excretion in people who were small at birth may be one mechanism explaining their increased risk of cardiovascular disease.

Urinary free deoxypyridinoline levels during childhood

Free urinary deoxypyridinoline (DPD) levels, corrected for the urinary concentration of creatinine (nmol/mmol), were determined in 144 healthy children (76 males and 68 females, mean age +/- SE: 9.1 +/- 0.2 yr, age range: 5.1-14.0 yr) in order to detect the possible age-related changes of this reliable index of bone resorption activity and the relationship between free DPD, gender and pubertal development. Multiple regression analysis revealed that most of the variation in DPD levels was explained by chronological age (coefficient: 2.89, p < 0.02), whereas sex and pubertal stage did not add significance to the variance. Urinary DPD levels were similar in males (24.7 +/- 1.8 nmol/mmol urinary creatinine) and females (24.2 +/- 2.0 nmol/mmol urinary creatinine) and significantly higher (p < 0.02) in pubertal (Tanner stage II-V: 28.6 +/- 2.8 nmol/mmol urinary creatinine) than in prepubertal children (22.4 +/- 1.4 nmol/mmol urinary creatinine), both in males and in females. The pattern of DPD levels was clearly different between females and males, the maximum increase being evident at Tanner stage II-III (mid-puberty) in females and at Tanner stage IV-V (mid-late puberty in males. The increase of DPD paralleled the elevation of urinary GH (pmol/mmol urinary creatinine), a non-invasive and acceptable index of physiological GH secretion, observed during the pubertal growth spurt. The progressive increase of urinary GH in older children was not followed by a further stimulation of bone resorption. Although the relationships between urinary, GH and DPD need to be better investigated, it seems plausible to hypothesize that the determination of urinary free DPD, as a marker of GH action on bone, might have some potential in the follow-up of growth promoting treatments, such as GH.