Reproducibility of 24-hour serum growth hormone profiles in man

Differential Diagnosis of the Short IGF-I-Deficient Child with Apparently Normal Growth Hormone Secretion

The current differential diagnosis for a short child with low insulin-like growth factor I (IGF-I) and a normal growth hormone (GH) peak in a GH stimulation test (GHST), after exclusion of acquired causes, includes the following disorders: (1) a decreased spontaneous GH secretion in contrast to a normal stimulated GH peak ("GH neurosecretory dysfunction," GHND) and (2) genetic conditions with a normal GH sensitivity (e.g., pathogenic variants of GH1 or GHSR) and (3) GH insensitivity (GHI). We present a critical appraisal of the concept of GHND and the role of 12- or 24-h GH profiles in the selection of children for GH treatment. The mean 24-h GH concentration in healthy children overlaps with that in those with GH deficiency, indicating that the previously proposed cutoff limit (3.0-3.2 μg/L) is too high. The main advantage of performing a GH profile is that it prevents about 20% of false-positive test results of the GHST, while it also detects a low spontaneous GH secretion in children who would be considered GH sufficient based on a stimulation test. However, due to a considerable burden for patients and the health budget, GH profiles are only used in few centres. Regarding genetic causes, there is good evidence of the existence of Kowarski syndrome (due to GH1 variants) but less on the role of GHSR variants. Several genetic causes of (partial) GHI are known (GHR, STAT5B, STAT3, IGF1, IGFALS defects, and Noonan and 3M syndromes), some responding positively to GH therapy. In the final section, we speculate on hypothetical causes.

Adults with pathogenic MC4R mutations have increased final height and thereby increased bone mass

Pathogenic mutations in the melanocortin-4 receptor (MC4R) are associated with obesity, increased linear growth, and higher bone mass in children, and rodent studies have indicated an effect of the MC4R on bone turnover. Furthermore, GLP-1 receptor agonists (GLP-1 RAs) may influence bone metabolism. However, these associations have not been assessed in adults with pathogenic MC4R mutations. Thus, we wished to assess the impact of the MC4R on bone mass and metabolism. Secondly, we wished to investigate the impact of the GLP-1 RA liraglutide on bone mass in adults with pathogenic MC4R mutations. 17 patients with obesity-causing MC4R mutations (BMI: 35.5 ± 7.6) and 35 matched control participants with common obesity (BMI: 34.3 ± 7.1) underwent a DEXA scan for assessment of bone mineral density (BMD), bone mineral apparent density [BMAD = (BMD/√(bone area)], and bone turnover markers (BTMs). Individuals with a BMI above 28 (14 MC4R mutation carriers and 28 matched control participants) underwent 16 weeks treatment with liraglutide 3.0 mg. The MC4R group had higher BMD [mean difference: 0.065 g/m² (- 0.008 to 0.138), p = 0.03], but BMAD and BTMS were not different compared to the control group. In response to liraglutide, BMAD increased in the control group, compared to no change in the MC4R group [mean group difference: 0.0007 (0.0001-0.001), p = 0.04]. In conclusion, BMD is increased in MC4R causal obesity compared to common obesity, but when corrected for body size (BMAD), bone mass was not increased, and no evidence of an influence of the MC4R on bone metabolism in adults was found. Liraglutide treatment did not change bone metabolism in MC4R causal obesity, but increased bone mass as measured by BMAD in common obesity.

Genetic determinants of growth hormone and GH-related phenotypes

Background

Higher fasting Growth Hormone (GH) has been associated with increased cardiovascular morbidity and mortality. Our objective was to find genetic determinants of fasting GH in order to facilitate future efforts of analyzing the association between fasting growth hormone and cardiovascular disease. A genome-wide association study (GWAS) was performed in a discovery cohort of 4134 persons (58% females; age 46–68 yrs), linking SNPs to fasting hs-GH. Fifteen SNPs were replicated in an independent cohort of 5262 persons (28.9% females; age 56–85 yrs). The best performing SNP was analyzed vs GH-related variables in a third independent cohort (n = 24,047; 61% females; age 44–73 yrs). A candidate gene approach searched for significant SNPs in the genes GH1 and GHR in the discovery cohort and was replicated as previously described.

Results

In the GWAS, the minor allele of rs7208736 was associated with lower GH in the discovery cohort (p = 5.15*10^-6) and the replication cohort (p = 0.005). The GH reducing allele was associated with lower BMI (P = 0.026) and waist (P = 0.021) in males only. In the candidate gene approach rs13153388 in the GHR-gene was associated with elevated GH-levels (P = 0.003) in the discovery cohort only and reduced height (P = 0.003).

Conclusion

In the first GWAS ever for GH, we identify a novel locus on chromosome 17 associated with fasting GH levels, suggesting novel biological mechanisms behind GH secretion and GH-related traits. The candidate gene approach identified a genetic variant in the GHR, which was associated with an elevation of fasting hs-GH and lower height suggesting reduced GHR ligand sensitivity. Our findings need further replication.

Electronic supplementary material

The online version of this article (10.1186/s12864-017-4219-z) contains supplementary material, which is available to authorized users.

Fasting levels of growth hormone are associated with carotid intima media thickness but are not affected by fluvastatin treatment

Background

Growth hormone (GH) has been linked to cardiovascular disease but the exact mechanism of this association is still unclear. We here test if the fasting levels of GH are cross-sectionally associated with carotid intima media thickness (IMT) and whether treatment with fluvastatin affects the fasting level of GH.

Methods

We examined the association between GH and IMT in 4425 individuals (aged 46–68 years) included in the baseline examination (1991–1994) of the Malmö Diet and Cancer cardiovascular cohort (MDC-CC). From that cohort we then studied 472 individuals (aged 50-70 years) who also participated (1994–1999) in the β-Blocker Cholesterol-Lowering Asymptomatic Plaque Study (BCAPS), a randomized, double blind, placebo-controlled, single-center clinical trial. Using multivariate linear regression models we related the change in GH-levels at 12 months compared with baseline to treatment with 40 mg fluvastatin once daily.

Results

In MDC-CC fasting values of GH exhibited a positive cross-sectional relation to the IMT at the carotid bulb independent of traditional cardiovascular risk factors (p = 0.002). In a gender-stratified analysis the correlation were significant for males (p = 0.005), but not for females (p = 0.09). Treatment with fluvastatin was associated with a minor reduction in the fasting levels of hs-GH in males (p = 0.05) and a minor rise in the same levels among females (p = 0.05).

Conclusions

We here demonstrate that higher fasting levels of GH are associated with thicker IMT in the carotid bulb in males. Treatment with fluvastatin for 12 months only had a minor, and probably not clinically relevant, effect on the fasting levels of hs-GH.

Electronic supplementary material

The online version of this article (doi:10.1186/s12872-017-0563-9) contains supplementary material, which is available to authorized users.

Analysis of Low Frequency Protein Truncating Stop-Codon Variants and Fasting Concentration of Growth Hormone

Background

The genetic background of Growth Hormone (GH) secretion is not well understood. Mutations giving rise to a stop codon have a high likelihood of affecting protein function.

Objectives

To analyze likely functional stop codon mutations that are associated with fasting plasma concentration of Growth Hormone.

Methods

We analyzed stop codon mutations in 5451 individuals in the Malmö Diet and Cancer study by genotyping the Illumina Exome Chip. To enrich for stop codon mutations with likely functional effects on protein function, we focused on those disrupting >80% of the predicted amino acid sequence, which were carried by ≥10 individuals. Such mutations were related to GH concentration, measured with a high sensitivity assay (hs-GH) and, if nominally significant, to GH related phenotypes, using linear regression analysis.

Results

Two stop codon mutations were associated with the fasting concentration of hs-GH. rs121909305 (NP_005370.1:p.R93*) [Minor Allele Frequency (MAF) = 0.8%] in the Myosin 1A gene (MYO1A) was associated with a 0.36 (95%CI, 0.04 to 0.54; p=0.02) increment of the standardized value of the natural logarithm of hs-GH per 1 minor allele and rs35699176 (NP_067040.1:p.Q100*) in the Zink Finger protein 77 gene (ZNF77) (MAF = 4.8%) was associated with a 0.12 (95%CI, 0.02 to 0.22; p = 0.02) increase of hs-GH. The mutated high hs-GH associated allele of MYO1A was related to lower BMI (β-coefficient, -0.22; p = 0.05), waist (β-coefficient, -0.22; p = 0.04), body fat percentage (β-coefficient, -0.23; p = 0.03) and with higher HDL (β-coefficient, 0.23; p = 0.04). The ZNF77 stop codon was associated with height (β-coefficient, 0.11; p = 0.02) but not with cardiometabolic risk factors.

Conclusion

We here suggest that a stop codon of MYO1A, disrupting 91% of the predicted amino acid sequence, is associated with higher hs-GH and GH-related traits suggesting that MYO1A is involved in GH metabolism and possibly body fat distribution. However, our results are preliminary and need replication in independent populations.

Fasting levels of high-sensitivity growth hormone predict cardiovascular morbidity and mortality: the Malmö Diet and Cancer study

BACKGROUND

Both pathological excess and deficiency of growth hormone (GH) are associated with cardiovascular mortality.

OBJECTIVES

The goal of this study was to test whether fasting levels of growth hormone measured with a high-sensitivity assay (hs-GH) predict cardiovascular morbidity and mortality at the population level.

METHODS

We studied 4,323 participants (age 46 to 68 years; mean age 58 years; 59% women) of the Swedish, population-based Malmö Diet and Cancer study examined in 1991 to 1994. Using multivariate-adjusted Cox proportional hazards models, we related baseline levels of fasting hs-GH to incidence of coronary artery disease, stroke, congestive heart failure, all-cause mortality, and cardiovascular mortality.

RESULTS

During a median follow-up of 16.2 years, hs-GH (hazard ratio [HR]/SD increment of natural logarithm of fasting hs-GH) was independently associated with increased risk of coronary artery disease (397 events; HR: 1.11; 95% confidence interval [CI]: 1.01 to 1.23; p = 0.04), stroke (251 events; HR: 1.18; 95% CI: 1.04 to 1.34; p = 0.01), congestive heart failure (107 events; HR: 1.25; 95% CI: 1.03 to 1.52; p = 0.02), all-cause mortality (645 events; HR: 1.17; 95% CI: 1.08 to 1.26; p < 0.001) and cardiovascular mortality (186 events; HR: 1.43; 95% CI: 1.24 to 1.66; p < 0.001). The addition of hs-GH to a model with conventional cardiovascular risk factors significantly reclassified risk, with a category-free net reclassification improvement (>0) of 0.542 (95% CI: 0.205 to 0.840) in cardiovascular mortality.

CONCLUSIONS

Higher values of hs-GH were associated with an increased risk of cardiovascular morbidity and mortality.

Complex rhythmicity of growth hormone secretion in humans

To better characterize the 24 hr GH secretion pattern in humans, we studied frequently sampled 24 hr GH profiles in 93 young (18-45 years of age) healthy, fed volunteers: men (n=67) and women (n=26) with BMI<26 kg/m(2). Analysis of the composite GH series in men revealed 3 significant GH "waves" with peaks occurring at midnight (p<0.0001), at noon (p<0.02) and at 1800 h (p<0.0001). In women, similar pattern was seen, with three GH "waves" peaking at midnight (p<0.0001), 1100 h (p<0.02) and at 1600 h (p<0.002). We conclude that the 24 hr rhythmicity of GH secretion is far more complex than currently appreciated. The attribution of the two daytime GH "waves" to food consumption is unlikely but cannot be excluded at the present time. The complex temporal pattern of pulsatile GH secretion may have important effects on regulation of target cell function.

The impact of hormone physiology on clinical practice with reference to two papers spanning 40 years of endocrinology

Following the pioneering work of Roger Ekins in describing the methodology for radioimmunoassay of hormone concentrations in plasma a series of publications followed describing variation in plasma hormone concentrations in a number of diseases. Though fluctuations in hormonal concentrations had been suspected, it was not until Hunter and Rigal documented these for the GH axis that it became apparent that the preferred mode of signalling for many hormone systems and in particular the anterior-pituitary hormones was of a pulsatile nature.

Rational use of the laboratory for childhood and adult growth hormone deficiency

No laboratory test has sufficient diagnostic sensitivity and specificity to serve as a gold standard for the diagnosis for GHD: therefore, test results must be interpreted after assessment of risk for GHD is determined on clinical grounds. Growth data are particularly crucial for diagnosis of childhood GHD;history of known pituitary damage and presence or absence of other pituitary hormone deficiencies are the critical elements for the diagnosis of adult GHD. New reference preparations are available for GH and IGF-I and should greatly aid interassay comparisons when the preparations are universally adopted.GH stimulation testing remains a key part of the diagnosis of adult GHD, but is currently being de-emphasized for the diagnosis of pediatric GHD. Better interassay comparative data and organized clinical collaboration between clinicians and test manufacturers/laboratories to set rational clinical diagnostic cutoffs would improve greatly the clinical usefulness of GH stimulation testing. The availability of statistically sound age- and sex-related normative data for IGF-I and IGFBP3 make these key tests for the diagnosis of childhood GHD. Although IGF-I may not be a perfect test for the diagnosis of adult GHD, it may be sufficiently informative in many cases to warrant using it ona routine basis. IGF-I also has a role in monitoring the safety of adult patients who are on GH treatment; studies are underway to determine if IGF-I may be useful in the future for optimization of GH dosaging.

Variability in growth hormone stimulation tests

The diagnosis of growth hormone deficiency (GHD) in adulthood has become increasingly important because of the approved indication for growth hormone (GH) substitution therapy in such patients. While GH stimulation tests are superior to single measurements of other growth factors or spontaneous GH secretion in the diagnosis in adults, the reproducibility and specificity of GH stimulatory tests are often described to be low. This is also the case with the insulin tolerance test. Many external factors, such as fasting, physical activity, heat exposure and sleep, are known to influence GH secretion. The stimulatory or inhibitory effect of these factors on GH secretion might, therefore, influence the GH provocative test and contribute to the variability in response. Age and body composition are also known to influence GH secretion, and these factors must be considered when evaluating GH test responses. However, age-related cut-off levels for GHD have not been defined. Obesity is still a complicating factor in the diagnosis of GHD, even though some GH tests have been able to distinguish between obesity and true GHD. Based on these complicating factors, the parameters of GH stimulatory tests are recommended to be defined and standardized to optimize reproducibility and specificity. Furthermore, such tests should be performed only in patients with firm evidence of pituitary disease.

Unique case of growth hormone (GH) deficiency accompanied by clinical anophthalmia, hypoplastic orbits, digital dysplasia, short stature, obesity, and diabetes mellitus

A 43-year-old female was admitted to our hospital for polydipsia and hyperglycemia. She had total blindness and globes were not recognized by inspection, indicating clinical anophthalmia. Physical examination revealed short stature, obesity, prematurely gray hair, shortness of fingers and toes, syndactyly, and multiple dental caries. Laboratory examination showed hyperglycemia, increased glycosilated hemoglobin (HbA1c) and insulin resistance on euglycemic glucose clamp. Blunted growth hormone (GH) secretion was shown in response to insulin-induced hypoglycemia, arginine infusion, and GH-releasing hormone (GHRH) loading test, and in 24 h spontaneous GH profile. Magnetic resonance imaging (MRI) and computed tomography (CT) showed dysostosis of orbit, defect of optic nerve, enlarged suprasellar cistern, and prolonged pituitary stalk. This may be the first report of a unique case with GH deficiency accompanied by clinical anophthalmia, hypoplastic orbits, digital dysplasia, short stature, obesity, and diabetes mellitus.

Hexarelin induced growth hormone release is influenced by exogenous growth hormone

OBJECTIVE

Growth hormone releasing peptides (GHRPs) are a group of synthetic compounds capable of releasing GH by an unknown mechanism. The aim of this study was to determine the effect of administering biosynthetic human growth hormone (rhGH) on the GH releasing activity of hexarelin, a new and potent GHRP, and to compare the results with those obtained with growth hormone releasing hormone (GHRH).

DESIGN

Boluses of saline or rhGH were administered intravenously, followed 90 minutes later by a second intravenous bolus of saline, hexarelin or GHRH. Studies were performed following an overnight fast. Each subject underwent six studies performed in a random order and separated by at least 2 days.

SUBJECTS

Six healthy adult males (23.8-34.3 years) were studied.

MEASUREMENTS

Serum GH and IGF-I levels were measured by radioimmunoassay.

RESULTS

The peak serum GH response to hexarelin was greater than that to GHRH, irrespective of whether the first bolus was saline (P < 0.05) or rhGH (P < 0.02). Prior administration of rhGH led to a reduction in peak serum GH response to hexarelin or GHRH (P < 0.05); the percentage reduction in response to hexarelin was less than that to GHRH, but this difference was not statistically significant (P = 0.3). There was no change in serum IGF-I concentration before or 90 minutes after the administration of rhGH.

CONCLUSIONS

Hexarelin is a potent GH secretagogue subject to partial feedback inhibition by rhGH. This raises issues about its mechanism of action and may have implications for its potential therapeutic use.

Defining growth hormone deficiency in adults

The absence of a distinct clinical syndrome calls for a strategy to reliably identify patients with hyposomatotropism. However, there is no consensus as to the most appropriate method of defining growth hormone (GH) deficiency in adults. Since GH secretion falls with senescence and is also reduced by obesity, both of these factors must be controlled for in such an evaluation. We have investigated the relative diagnostic merits of measuring (1) peak GH response to insulin-induced hypoglycemia (ITT), (2) mean 24-hour GH concentration derived from 20-minute sampling (IGHC), (3) serum IGF-I levels, and (4) serum insulin-like growth factor (IGF)-binding protein-3 (IGFBP-3) levels. These tests were undertaken in 23 patients considered GH-deficient from extensive organic pituitary disease and in 35-sex-matched normal subjects of similar age and body mass index. The ITT was the only test capable of distinguishing patients with organic GH deficiency from matched normal subjects. The sensitivity of the GH radioimmunoassay (0.2 ng/mL) limited the utility of IGHC measurements, since many subjects from both groups had undetectable values. Using a GH assay with a 100-fold greater sensitivity, we found a better but still incomplete separation of values between the two groups. There was a significant overlap of IGF-I and IGFBP-3 values, with only a third of GH-deficient subjects having low IGF-I values. The limitation of IGF-I has been confirmed by others, although its sensitivity as a diagnostic test is greater in young adults. We conclude that organic GH deficiency in adults can be reliably diagnosed by the ITT.(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of a continuous infusion of a somatostatin analogue (octreotide) for two years on growth hormone secretion and height prediction in tall children

OBJECTIVE

Strategies to limit the final height of tall children have centred on the use of high doses of sex steroids to advance skeletal maturation. This limits therapy to the peripubertal years whereas the greatest gain in height is in the prepubertal years. Prepubertal growth is largely GH dependent and previous work has documented modulation of GH secretion by once or twice daily subcutaneous injection of the somatostatin analogue octreotide. In this study we have determined the effects of a nocturnal infusion of octreotide on height prediction, GH and TSH secretion in tall children.

DESIGN

A patient controlled study in which height prediction and 24-hour GH and TSH secretion were compared prior to and during the course of a 2-year treatment programme with a nocturnal infusion of octreotide in a dose of 1-1.5 micrograms/kg body weight given subcutaneously.

PATIENTS

Nine tall children (4M; 5F) aged 7-14 years with final height predictions of 179 cm or greater in the girls and between 183 and 202 cm in the boys were studied.

MEASUREMENTS

Height prediction using the Tanner-Whitehouse system prior to and at the end of 2 years of treatment. Twenty-four-hour serum GH and TSH concentration profiles, thyroxine, IGF-I and GH responses to GHRH(1-29)NH2 were studied prior to and at the end of the first year of therapy.

RESULTS

Treatment with octreotide led to a significant reduction in height prediction in 7 of the 8 children who completed treatment (median reduction 3.5 cm, range +2.8 to -11.5; Wilcoxon, P = 0.05). Twenty-four-hour mean serum GH concentration decreased by 50% (MANOVA, P = 0.03) during therapy and this was accompanied by an increase in the percentage of samples giving values less than 0.5 mU/l (MANOVA, P = 0.02). There was no overall change in the serum GH response to GHRH(1-29)NH2 or serum IGF-I concentrations. Nocturnal serum TSH concentrations were reduced to levels observed during the daytime but these changes had no effect on serum thyroxine values. One patient developed gallstones during the course of therapy.

CONCLUSIONS

A nocturnal infusion of octreotide reduces GH secretion and height prediction in tall children. Therapy with somatostatin analogues allows a reduction in growth rate to be instigated in the prepubertal years reducing the actual height from which will commence the pubertal growth spurt.

Growth and the growth hormone axis in prepubertal children with asthma

To determine the influence of asthma and its treatment with inhaled corticosteroids on growth, linear growth velocity, and the growth hormone axis in prepubertal children, we performed a longitudinal study for 12 months in 56 children with asthma, aged between 4.4 and 11.7 years. Height, weight, skin-fold thickness, and lung function were measured every 3 months and bone age at entry to and exit from the study. A 24-hour serum growth hormone concentration profile and fasting insulin-like growth factor I levels were measured halfway through the year. Seventy-four percent of boys and 62% of girls had heights below the 50th percentile. Growth velocity in the nonsteroid-treated control group (n = 13) was normal; 10 of 20 children taking beclomethasone grew slowly (14/20 used a dry powder device), and 4 of 19 children taking budesonide grew slowly (15/19 used a spacer). Three of four children using inhaled steroids and prednisolone grew slowly. In none of the treatment groups were measures of growth hormone secretion or levels of radioimmunoassayable serum insulin-like growth factor I affected. We conclude that slow growth in steroid-treated children with asthma does not appear to be associated with major perturbations in the growth hormone axis.

Reversibility of physiological growth hormone secretion in children with psychosocial dwarfism

OBJECTIVE

Reversibility of GH insufficiency with a change of environment is characteristic of psychosocial dwarfism, and excludes an organic endocrinopathy. However, the change in GH pulsatility has not previously been described. We therefore wished to study spontaneous GH secretion before and after change to a more favourable environment in 11 children with psychosocial deprivation and short stature in order to evaluate if separation from the families can modify their patterns of GH secretion.

PATIENTS AND DESIGN

We describe 11 prepubertal children (6 M and 5 F; 2.2-13.5 years of age) who had growth failure and psychosocial deprivation. They were diagnosed by a multidisciplinary team as having environmental growth failure after admission to hospital for 3 weeks. Six of them were discovered to have been sexually abused. During the uninterrupted hospital admission parental access was restricted. Three sets of 18-hour GH profiles were performed on each child, except one child who had only two, during the 3-week admission.

MEASUREMENTS

Pulse analysis of GH profiles was by Fourier transformation.

RESULTS

On the first day of admission spontaneous GH secretion demonstrated a spectrum of abnormalities in the pattern of basal values, pulse frequency and pulse amplitude. Such GH insufficiency showed reversibility during the 3 weeks in hospital. Indeed, there was a significant increase in GH secretion which was amplitude modulated without any significant modification in pulse frequency.

CONCLUSION

Our data indicate that there is abnormal physiological GH secretion in children with psychosocial deprivation, which is associated with growth failure. Despite a pathological situation, each child retained his own characteristic pattern of GH pulsatility. The pattern of reversibility of abnormal GH pulsatility provides information for the mechanism of the control of GH secretion.

Diagnosis of growth-hormone deficiency in adults

There is no consensus as to the most appropriate method of diagnosing growth-hormone (GH) deficiency in adults. We have evaluated the relative diagnostic merits of measuring peak GH response to insulin-induced hypoglycaemia (insulin tolerance test), mean 24 h GH concentration derived from 20 min sampling, serum insulin-like growth factor I (IGF-I) concentrations, and serum IGF binding protein 3 (IGFBP-3) concentrations. These tests were undertaken in 23 patients considered GH deficient from extensive organic pituitary disease, and in 35 sex-matched normal subjects of similar age and body-mass index. Hypopituitary subjects had significantly lower stimulated peak GH, mean 24 h GH, IGF-I, and IGFBP-3 concentrations than normal subjects. The ranges of stimulated peak GH responses were clearly separated between the hypopituitary (< 0.2-3.1 ng/mL) and normal (5.3-42.5 ng/mL) groups, but mean 24 h GH, IGF-I, and IGFBP-3 concentrations overlapped. Mean 24 h GH concentrations were below assay sensitivity in 80% of hypopituitary subjects and 16% of normal subjects. 70% and 72%, respectively, of the IGF-I and IGFBP-3 values in hypopituitary subjects were within the range for normal subjects. We conclude that GH deficiency in adults is most reliably identified by stimulatory testing, and that IGF-I and IGFBP-3 are poor diagnostic tests of adult GH deficiency.

The effects of recombinant human insulin-like growth factor I on growth hormone secretion in adolescents with insulin dependent diabetes mellitus

OBJECTIVE

It has been proposed that low IGF-I levels and reduced IGF-I bioactivity may lead to elevated GH levels in adolescents with insulin dependent diabetes (IDDM). We have therefore studied the effects of human recombinant insulin-like growth factor I (rhIGF-I) administration on GH levels and GH secretion in adolescents with IDDM.

PATIENTS

Nine late pubertal adolescents (four male and five female) with IDDM.

DESIGN

A double-blind placebo controlled study of rhIGF-I administered subcutaneously in a dose of 40 micrograms/kg body weight at 1800 h.

MEASUREMENTS

IGF-I and GH concentrations were measured at regular intervals throughout the study. Twenty-two hour GH secretory rates were calculated by deconvolution analysis. Overnight GH profiles were analysed by distribution analysis, and Fourier transformations were performed on both overnight GH concentrations and GH secretory rates.

RESULTS

Mean IGF-I levels over the 22-hour study period were significantly elevated following rhIGF-I administration (350 +/- 26 vs 205 +/- 21 micrograms/l (mean +/- SEM), P < 0.01). Mean 22-hour GH levels were reduced following rhIGF-I administration (19.4 +/- 4.0 compared with 33.6 +/- 5.8 mU/l; P = 0.01). Distribution analysis demonstrated that the reduction in GH levels was due to changes in the proportion of values at both high and low concentrations. Deconvolution analysis also revealed a significant overall reduction in GH secretory rate following IGF-I administration (1.81 +/- 0.30 vs 2.98 +/- 0.47 mU/min, P = 0.01) which was still apparent during the final 5.5 hours of the study period (1.51 +/- 0.30 vs 2.76 +/- 0.61 mU/min, P = 0.02). The dominant periodicity of GH secretory episodes as determined by Fourier transformation was between 120 and 180 minutes after both IGF-I and placebo.

CONCLUSIONS

In late pubertal adolescents with IDDM the rise in IGF-I levels following rhIGF-I administration in a subcutaneous dose of 40 micrograms/kg body weight leads to a significant reduction in GH levels and GH secretory rate. The reduction in GH secretion is due to changes in pulse amplitude rather than frequency. A reduction in GH secretion was apparent at the beginning and also towards the end of the 22-hour study period.

Immunolike growth hormone substance in tissues from human embryos/fetuses and adults

GH immunolike reactivity was measured by RIA and IRMA tests in the extracts of tissues from human fetuses (8-32 weeks) and adults. For some fetal tissues a comparison was made with the T4 values obtained in a previous study. Both hormones were already measurable in peripheral tissues at 8 weeks of gestation. The increase in GH was faster than for T4 and it reached the zenith at approximately 20 weeks; thereafter, the GH concentration declined until delivery. In contrast, T4 progressively increased until term. Thirteen tissues were studied both in fetuses and in adults: the GH concentration was about 10 times higher in fetal tissues, with the exception of the brain and the pancreas. The brain showed the lowest GH concentration throughout fetal life and adulthood, whereas the highest GH levels were recorded in adults' pancreas, but they resulted to be artifacts since the RIA values were not confirmed by the IRMA test. In both groups of subjects the highest GH concentrations were found in kidneys, liver and small intestine; the lowest, beyond the brain, in red muscle and cartilage. Thus, the pattern of the quantitative distribution of GH in fetal tissues is the same as in adults, suggesting a functional role of the hormone in the developing human during the prenatal period, in contrast with the concept that high tissue levels of GH are a mere reflection of high GH blood levels. Moreover, in all tissues examined no correlation was found between GH and T4 concentration.

The effects of oxandrolone on the growth hormone and gonadal axes in boys with constitutional delay of growth and puberty

OBJECTIVE

We studied the effects of oxandrolone on serum concentrations of LH, FSH, testosterone, GH, SHBG, DHEAS, IGF-I and insulin in boys with constitutional delay of growth and puberty.

DESIGN

Ten boys with constitutional delay of growth and puberty, mean age 13.8 years (range 12.4-15.5) were studied. Twenty-four-hour serum concentration profiles of GH, LH and FSH were constructed by drawing blood samples at 20-minute intervals. Three study occasions over a period of 6 months were chosen to assess hormone concentrations before, during and 6 weeks after a 3-month course of oxandrolone (2.5 mg once daily) therapy.

RESULTS

Growth velocity increased during oxandrolone treatment and stayed higher after therapy (pre 3.9 +/- 0.5; on 6.3 +/- 0.8; post 6.4 +/- 0.9 cm/year (mean +/- SEM) two way ANOVA, F = 5.3, P = 0.02). Oxandrolone had androgenic effects, suppressing mean serum LH concentrations from 1.7 +/- 0.3 to 1.1 +/- 0.2 U/I and serum testosterone concentrations from 1.9 +/- 0.6 to 0.8 +/- 0.1 nmol/l. SHBG concentrations were also reduced from 130.9 +/- 14.6 to 30.7 +/- 7.3 nmol/l. Serum GH concentration fell slightly from 5.9 +/- 0.6 to 4.8 +/- 0.5 mU/l. After cessation of treatment, there was a significant 'rebound' in mean 24-hour serum LH (2.6 U/l +/- 0.4) and testosterone concentrations (3.2 +/- 0.9 nmol/l) but no change in serum GH concentrations. SHBG values also rose but not to the same extent as those observed before therapy (82.0 +/- 8.4 nmol/l). There were no statistically significant differences in serum concentrations of FSH, DHEAS, IGF-I and insulin over the study period. In a stepwise multiple regression analysis of factors that might influence the growth rate observed, the 24-hour mean serum testosterone concentration and the treatment (on or off) with oxandrolone were the main influences. The relationship was described by the equation Height velocity = 0.69 (24-hour mean serum testosterone concentration)+1.70 (treatment regimen)+3.37 (adjusted R2 = 0.35, F = 8.39, P = 0.001).

CONCLUSIONS

Oxandrolone has an androgenic action as shown by changes in serum LH, testosterone and SHBG concentrations and by the lack of effect on FSH. No effect of oxandrolone on the GH axis was documented. We suggest that the growth promoting effects of oxandrolone are related in part to the mild androgenic effects of the steroid and the growth acceleration following oxandrolone withdrawal may reflect increasing total serum testosterone concentrations and decreasing levels of SHBG and progress in puberty.

The relationship between endogenous testosterone and gonadotrophin secretion

OBJECTIVE

The secretion of luteinizing hormone (LH), follicle stimulating hormone (FSH) and testosterone in the adult male was studied by means of 48-hour profiles. The aim of the study was to examine the effects of the endogenous circadian variation in serum testosterone concentration on LH pulsatility, and to determine the temporal relationships between FSH and LH, and between LH and testosterone by cross-correlation, and the pulse frequency of these hormones by spectral analysis, as revealed by extended sampling periods.

DESIGN

Hormone profiles were obtained by 20-minute sampling over 48 hours.

SUBJECTS

Six healthy adult males, aged between 21 and 23 years.

MEASUREMENTS

LH and FSH were measured using an immunoradiometric assay and testosterone with a solid-phase radioimmunoassay.

RESULTS

The profiles showed pulsatile secretion of all three hormones, and a circadian rhythm with levels highest between 0200 and 0600 h. Cross-correlation analysis: There was a significant relationship between LH and FSH (r = 0.5; P = 0.001) at 0 minutes (i.e. no time lag). A pulse of testosterone followed on average 60 minutes after a pulse of LH (r = 0.26; P = 0.001). Fourier transformation: Spectral analysis showed the dominant period for LH and FSH pulsatility to be 200 minutes. The dominant period for testosterone pulsatility was 400 minutes. The effect of endogenous variations in serum testosterone concentrations: The LH profiles were divided into periods when the serum testosterone concentration was high or low, and Fourier transformation carried out on these shorter periods. These transforms showed that the dominant period during high serum testosterone concentration was 180 minutes, and during low serum testosterone was 120 minutes (P < or = 0.025).

CONCLUSIONS

FSH and LH are co-secreted, and a pulse of testosterone follows a pulse of LH by 60 minutes. The physiological changes in serum testosterone concentration that occur during the day result in changes in the pulse frequency of LH. Testosterone concentrations thus have rapidly acting feedback activity at hypothalamic level.

Analysis of trough serum growth hormone concentrations: comparison of an immunoradiometric assay and a sensitive ELISA for growth hormone

OBJECTIVES

We compared a sensitive assay for GH (ELISA) with a conventional immunoradiometric (IRMA) assay with particular reference to the oscillatory activity detected by Fourier transformation and the estimation of trough concentrations using occupancy analysis.

DESIGN

Eight healthy adult male volunteers underwent 24-hour profiles during which samples were drawn at 20-minute intervals. Samples were analysed by an ELISA and an IRMA system.

MEASUREMENTS

The 24-hour serum GH concentration profiles were subjected to Fourier transformation and to occupancy analysis.

RESULTS

No additional GH periodicities could be determined in the ELISA data other than the well documented 180-200-minute periodicity. Median observed concentrations (OC) at 5% occupancy were 0.035 mU/l (range 0.004-0.22) for the ELISA and 0.035 mU/l (range 0.001-0.50) for the IRMA. For all OC parameters, 5, 50 and 95%, there was a good correlation between the ELISA and IRMA systems. The mean difference (bias) between the ELISA and IRMA were -0.05, -0.28 and -1.40 mU/l at OC values of 5, 50 and 95% respectively and the standard deviations of the difference at the same OC values were 0.10, 0.50 and 1.61 mU/l.

CONCLUSION

Although there is a qualitative improvement on visual inspection of individual 24-hour serum GH profiles obtained using the ELISA system, there is little additional information gained in terms of pulse periodicity or occupancy analysis.

Rate of change (modulation) of serum growth hormone concentrations is a more important factor in determining growth rate than duration of exposure

OBJECTIVE

To determine whether duration of exposure to GH and/or rate of change of serum GH concentration are important factors in determining the growth rate of short children.

DESIGN

An analysis of parameters of occupancy percentage and rate of change of serum GH concentration was performed as part of a prospective study investigating the relationship between growth and GH in childhood.

PATIENTS

Sixty-four short prepubertal children (48 male, 16 female) aged between 4.7 and 11.9 years were studied. Thirty-one children were growing with a height velocity standard deviation score between 0 and -0.8 and were defined as short normal. Thirty-three children were growing with a height velocity standard deviation score less than -0.8 and were defined as short slowly growing.

MEASUREMENTS

Twenty-four hour serum GH concentration profiles were constructed by withdrawing samples at 20-minute intervals. Analysis of occupancy percentage was performed on each data array by determining cumulative distributions and plotting these as linear probits against log serum GH concentration. Estimates of peak (OC95), intermediate (OC50) and trough (OC5) occupancies were calculated. A first-order derivative of the concentration-time data array was determined for each profile as a measure of rate changes.

RESULTS

First-order derivative values were significantly greater in the short normal group than in the short slowly growing children (short normal median 1.41 mU/l/min; short slowly growing median 0.72 mU/l/min; P less than 0.001). OC95 values were significantly higher in the short normal group (median 19.31 mU/l) than the short slowly growing group (median 7.69 mU/l) (P less than 0.001). There was no difference in OC50 values. OC5 values were lower in short normal children (median 0.20 mU/l) than in the short slowly growing children (0.55 mU/l) (P less than 0.003). The most important factor in determining growth rate was the rate of change in serum GH concentration (FOD). Occupancy percentage played no part in the relationship. The regression equation was Height velocity SDS = 1.16 (In FOD) - 1.03; r = 0.75; P less than 0.001

CONCLUSIONS

These data suggest that the pattern of presentation of GH in the circulation is an important factor in determining target organ response. Although occupancy percentages at differing serum GH concentrations differ between short slowly growing and short normal children, it is the rate of change of the hormone in the circulation which appears to be the more important 'signal' in terms of modulating growth.