Circulating immunoreactive growth hormone releasing hormone concentrations and growth hormone response to growth hormone releasing hormone in short children

To study the role of peripheral immunoreactive growth hormone releasing hormone (ir-GHRH) concentrations and the GHRH test in the evaluation of growth hormone (GH) secretion in short stature, 46 children with a mean age of 9.4 years (range 1.6–16.3 years) and a mean relative height score of –3.2 SD (range –5.0–2.1 SD) were investigated. The children were divided into prepubertal (n=35) and pubertal (n=11) and the prepubertal children further into three groups based on their maximal GH responses to insulin-induced hypoglycaemia (IIH) and clonidine: (1) GH deficient subjects (maximal GH<10 g/l in both test); (2) discordant responders (maximal GH<10 g/l in one test and 10 g/l in the other); and (3) normal responders (maximal GH10 g/l in both test). Peripheral ir-GHRH concentrations were measured during the IIH test by radioimmunoassay after purification of plasma samples on Sep-pak cartridges. Among the prepubertal children 10 fell into group 1, 16 into group 2 and 9 into group 3. Children in group 1 were older, than those in group 3. There were no significant differences in relative heights and weights or absolute and relative growth velocities between the groups. Subjects in groups 1 and 2 had lower maximal GH responses to GHRH than those in group 3. There were no significant differences in the basal plasma ir-GHRH concentrations between the groups. Nine children (19.6%) had somatotrophs with a poor response to a single dose of exogenous GHRH (maximal GH<10 g/l). These subjects had increased basal plasma ir-GHRH concentrations. All of them had a decreased GH response to IIH and/or clonidine. Pubertal children had higher circulating ir-GHRH levels than the prepubertal subjects. There was an inverse correlation (r=–0.46;P<0.001) between the maximal GH response to GHRH and calendar age in the whole series. These observations suggest that: (1) a substantial proportion of short children have a heterogenous GH response to pharmacological stimuli necessitating complementary evaluation of their spontaneous GH secretion; (2) a poor response to exogenous GHRH is associated with increased ir-GHRH levels in the peripheral circulation; (3) all children with normal GH responses in pharmacological tests respond normally to GHRH and (4) the pituitary sensitivity to GHRH decreases with increasing age. Peripheral ir-GHRH concentrations do not differentiate between short children with growth hormone deficiency (GHD) and those with undefined short stature. The GHRH test is of limited value in the diagnosis of GHD, since a normal GH response does not exclude GHD, although a subnormal response appears to reflect dysfunctional GH secretion.     

Comparison of growth hormone releasing hormone therapy and growth hormone therapy in growth hormone deficiency

Seven children with growth hormone deficiency of hypothalamic origin responded to an i.v. bolus of growth hormone releasing hormone (GHRH) (1–29)-NH2 with a mean serum increase of 10.7 ng/ml growth hormone (GH) (range 2.5–29.3 ng/ml). Continuous s.c. administration of GHRH of 4–6 g/kg twice daily for at least 6 months did not improve the growth rate in five of the patients. One patient increased his growth rate from 1.9 to 3.8 cm/year and another from 3.5 to 8.2 cm/year; however, the growth rate of the latter patient then decreased to 5.4 cm/year. When treatment was changed to recombinant human growth hormone (rhGH) in a dose of 2 U/m² daily, given s.c. at bedtime, the growth rate improved in all patients to a mean of 8.5 cm/year (range: 6.2 to 14.6). Presently GHRH cannot be recommended for the routine therapy of children with growth hormone deficiency since a single daily dose of rhGH produced catch-up growth which GHRH therapy did not.Abbreviations GH growth hormone - GHD growth hormone deficiency - GHRH growth hormone releasing hormone - hGH human growth hormone - rhGH recombinant human growth hormone - SM C/IGF I somatomedin C/insulin-like growth factor I On the occasion of the 85th birthday of Prof. Dr.Dr.h.c. mult. Adolf Butenandt     

Growth hormone releasing hormone and growth hormone: genetic studies in familial growth hormone deficiency

Four families with growth hormone (GH) deficiency, either isolated or with other pituitary hormonal deficits are described. Members of each underwent pharmacological testing for GH secretion and infusions of GH releasing hormone (GHRH) to determine the locus of the defect in GH secretion. In addition, we have extracted DNA from white blood cells to characterize the GHRH and GH genes. All members tested had the normal complement of GH and GHRH genes. Four generations of one family with isolated GH deficiency, autosomal dominant were studied. The younger members showed minimal GH responsiveness to a single infusion of GHRH. However, the older members did not respond even after 30 doses of GHRH given intravenously every 3 h. Two members of a family with the autosomal recessive type of isolated GH deficiency had large GH increases after GHRH infusion. Thus in these families the GH secretory defect lies within the hypothalamus. Members of two families with pituitary deficiency (GH and other tropic hormones) of the autosomal recessive type had variable responses to GHRH and varying amounts of pituitary tissue seen on high resolution CT scans. Although it is not possible to delineate the precise location of the secretory defects in these latter two families, a hypothalamic defect is probable based on the responses to multiple trophic stimuli. Heterogeneity of structure and function exists within and between families with isolated GH deficiency and within and among families with pituitary deficiency. It is from the study of such families in which all members presumably have the same underlying defect that one can more readily decide on a pathogenetic mechanism.     

Growth hormone releasing hormone. Review

Growth hormone-releasing hormone was isolated 1982 from human pancreatic tumours. They were found to consist of three peptides (GHRH1-44, GHRH1-40, GHRH1-37) which in vivo and in vitro were specific stimulators of pituitary growth hormone secretion. These tumor-derived GHRHs were demonstrated to be identical to human hypothalamic GHRHs. Extrahypothalamic GHRH is present in some brain regions and in the gastrointestinal tract. Circulating GHRH is detectable in human plasma, but little is known about its function. Above all binding of GHRH to a specific receptor stimulates growth hormone secretion through formation of cyclic AMP. GHRH secretion is modulated by somatostatin, the somatomedins and growth hormone itself. Following single injection of GHRH1-44 i.v. the equilibration half-time is 1.0 +/- 0.2 min and elimination half-time is 6.8 +/- 1.2 min. Maximal growth hormone response is achieved after injection of 1 microgram/kg GHRH. Using higher GHRH-doses growth hormone can be stimulated via subcutaneous or intranasal application. A single i.v. GHRH-test is not sufficient to prove a pituitary defect since growth hormone can be stimulated following repetitive injections in some cases. About 50% of patients with growth hormone deficiency have a hypothalamic defect of GHRH release. In some of these patients GHRH s.c. can promote linear growth to the same degree as growth hormone treatment.     

Growth hormone secretion following administration of growth hormone releasing hormone in constitutional short stature and idiopathic growth hormone deficiency

A stimulation test using 1 microgram growth-hormone-releasing factor (GRF 1-29 X NH2)/kg bodyweight was performed in children with familial short stature and in children with constitutional delay of growth and development. The GH secretion induced by this means was not different in these groups, but there was a difference in the response between normal children and children with idiopathic growth hormone deficiency (GHD). GH secretion after GRF administration was significantly lower in the GHD group than in the other groups. However, 6 of 24 patients with GHD responded to the test with a normal increase in GH (greater than 10 ng/ml), and 11 with an intermediate response (2-10 ng/ml). Thus, the test does not differentiate individual patients with defective growth hormone secretion from normal short children.     

Human growth hormone therapy of non-growth hormone deficient children

With biosynthetically derived human growth hormone (hGH) available in large quantities, attempts will be made to promote growth in short children who do not fulfill the 'classical' criteria for growth hormone deficiency (GHD). By these criteria, GHD is excluded if hGH levels to pharmacological stimuli exceed a definite level. Several studies have shown that a variety of short children, who are not growth hormone deficient by these criteria, will demonstrate an increased growth rate with hGH treatment. A subpopulation of children with clinical features of GHD, delayed bone age and low somatomedin levels, have low levels of spontaneously secreted growth hormone or 'bioinactive' growth hormone. These children increase their growth rates to substitution doses of hGH. In other children whose growth disorder is not likely to be caused by a disorder in the growth hormone-somatomedin axis, growth increments are occasionally seen on higher hGH doses. Future long-term studies--carefully considering the ethics of such approaches--will have to evaluate the relationships between hGH dose and both metabolic and growth responses and side effects in children with short stature in order to define more specifically further target groups of short children who will benefit from hGH therapy.     

Oral administration of arginine enhances the growth hormone response to growth hormone releasing hormone in short children

We have evaluated the effect of oral administration of arginine chlorhydrate on the growth hormone response to growth hormone releasing hormone in a group of nine short prepubertal children (six boys and four girls). Arginine chlorhydrate 10 g, administered orally 60 min before an iv bolus injection of growth hormone releasing hormone 1–29, 1 μg/kg, significantly enhanced the growth hormone response to the neuropeptidc, confirming the results of previous studies which used the iv route. Furthermore, our data strengthen the view that the effects of arginine chlorhydrate on growth hormone secretion are mediated by inhibition of endogenous somatostatin release.     

Changes with growth hormone treatment in growth hormone deficient children

A total of 54 previously untreated patients (15 girls, 39 boys) with poor growth due to idiopathic growth hormone deficiency (IGHD) were treated with human growth hormone (hGH), continuously up to 4 years. All of the patients had a peak hGH level which was below 10 ng/mL after at least two pharmacological tests and/or blunted physiologic hGH secretion, and their height was below ?2.5 s.d. for age and gender. After the 1st year of therapy, height velocity (HV) increased significantly when compared with baseline (from 3.18 ±0.76 cm/year to 9.17±1.03 cm/year; P <0.001), declined during the 2nd year and then remained significantly higher than pretreatment HV. When considering improvement in height expressed by height standard deviation score (SDS), during the therapy all of the patients showed a significant gain ± 1.72±1.09 (from ?4.11±0.61 to ?2.21±0.48). The height values were significantly higher than pretreatment, but remained below ?2 s.d. after 4 years of hGH therapy in our patients. Increased height velocity has been sustained, but height improvement after therapy was inversely correlated to height SDS for chronological age of patients at the start of therapy. In conclusion post-treatment height has been shown to be related to height deficit at the beginning of therapy. Therapy was well tolerated with no local or systemic adverse effects or acceleration of bone age.     

Screening for growth hormone deficiency using urinary growth hormone measurement

The diagnostic approach in growth hormone deficiency (GHD) is complicated. Two or more provocative tests are essential for definitive diagnosis of GHD. However, such testing cannot be carried out routinely on all subjects with short stature because of the need for hospitalization and blood sampling. A simple screening method for GHD would be of great value. Human growth hormone (hGH) levels were measured in the early morning urine of 192 children aged 7–15 years with height 2.0 s.d. below the mean for their ages. Sixty-eight subjects were selected because they showed a urinary hGH level < 10 ng/g creatinine. They were further examined in terms of bone age and plasma insulin-like growth factor (IGF-I) levels. In 30 subjects, the ratio of bone age: chronological age was < 0.8 and/or plasma IGF-I level was < 0.7 U/mL. Finally 24 of these subjects were examined with provocative tests and other endocrinological tests. Eleven subjects proved to have poor growth hormone secretion and one subject was diagnosed as having Turner syndrome. In conclusion, 11 patients with GHD were diagnosed from 192 children with short stature using urinary hGH measurement as the first screening method. These findings suggests that urinary hGH measurement could be a useful and simple method for detecting GHD.     

Oral administration of arginine enhances the growth hormone response to growth hormone releasing hormone in short children

We have evaluated the effect of oral administration of arginine chlorhydrate on the growth hormone response to growth hormone releasing hormone in a group of nine short prepubertal children (six boys and four girls). Arginine chlorhydrate 10 g, administered orally 60 min before an iv bolus injection of growth hormone releasing hormone 1–29, 1 μg/kg, significantly enhanced the growth hormone response to the neuropeptidc, confirming the results of previous studies which used the iv route. Furthermore, our data strengthen the view that the effects of arginine chlorhydrate on growth hormone secretion are mediated by inhibition of endogenous somatostatin release.     

Growth hormone responses to growth hormone releasing factor in neonates

The response of growth hormone (GH) to synthetic human growth hormone releasing factor (hGRF) administered intravenously was examined in 32 neonates aged 3-28 days. GH peaked at 30 min after hGRF administration and the mean +/- SEM level of GH at maximal response was 66.4 +/- 6.2 ng/ml. In the comparison between the neonates less than 7 days old and those more than 8 days old, between the neonates less than 37 weeks and those more than 38 weeks in gestational age, between the neonates under 2,500 g and those over 2,501 g in birth body weight, and between males and females, no significant statistical differences were observed.