Responses to analogues of growth hormone-releasing hormone in normal subjects, and in growth-hormone deficient children and young adults

Once-daily administration of CJC-1295, a long-acting growth hormone-releasing hormone (GHRH) analog, normalizes growth in the GHRH knockout mouse

Although the majority of children with isolated growth hormone (GH) deficiency have a good growth response to GH-releasing hormone (GHRH), the use of this therapeutic agent is limited by its very short half-life. Indeed, we have shown that, in mice with GHRH gene ablation (GHRH knockout; GHRHKO), even twice-daily injections of a GHRH analog are unable to normalize growth. CJC-1295 is a synthetic GHRH analog that selectively and covalently binds to endogenous albumin after injection, thereby extending its half-life and duration of action. We report the effects of CJC-1295 administration in GHRHKO animals. Three groups of 1-wk-old GHRHKO mice were treated for 5 wk with 2 microg of CJC-1295 at intervals of 24, 48, and 72 h. Placebo-treated GHRHKO mice and mice heterozygous for the GHRHKO allele served as controls. GHRHKO animals receiving daily doses of CJC-1295 exhibited normal body weight and length. Mice treated every 48 and 72 h reached higher body weight and length than placebo-treated animals, without full growth normalization. Femur and tibia length remained normal in animals treated every 24 and 48 h. Relative lean mass and subcutaneous fat mass were normal in all treated groups. CJC-1295 caused an increase in total pituitary RNA and GH mRNA, suggesting that proliferation of somatotroph cells had occurred, as confirmed by immunohistochemistry images. These findings demonstrate that treatment with once-daily administration of CJC-1295 is able to maintain normal body composition and growth in GHRHKO mice. The same dose is less effective when administered every 48 or 72 h.

Pharmacodynamic evaluation of a PEGylated analogue of human growth hormone releasing factor in rats and pigs

The aim of this study was to assess the in vivo efficacy of monoPEGylated GRF(1-29)NH(2) having one PEG(5000) chains attached to either lysine 12 or 21 as compared to the GRF(1-29)NH(2) in rats and pigs. This analogue termed GRF-1PEG(5000) was tested after a single intravenous administration in rats and after a single intravenous or subcutaneous injection in pigs. After 1 h administration, GH concentrations returned to values close to controls in the group of rats injected with GRF(1-29)NH(2). In animals injected with the same dose of GRF-1PEG(5000), the AUC values corresponding to the whole period 0.5-48 h and particularly to the 0.5-8 h period were higher than in the placebo or in the GRF(1-29)NH(2) groups. Interestingly, two additional peaks were observed at about 6 and 8 h following administration. An increase in the response of the endogenous GH peaks was also observed in pigs administered GRF-1PEG(5000) by intravenous route. When GRF-1PEG(5000) was administered subcutaneously to pigs, a significant increase, as compared to placebo and GRF(1-29)NH(2,) in both GH and IGF-I levels was observed. This new analogue might find therapeutic application in paediatric growth hormone deficiency or in aging.

Pathophysiology of the neuroregulation of growth hormone secretion in experimental animals and the human

During the last decade, the GH axis has become the compelling focus of remarkably active and broad-ranging basic and clinical research. Molecular and genetic models, the discovery of human GHRH and its receptor, the cloning of the GHRP receptor, and the clinical availability of recombinant GH and IGF-I have allowed surprisingly rapid advances in our knowledge of the neuroregulation of the GH-IGF-I axis in many pathophysiological contexts. The complexity of the GHRH/somatostatin-GH-IGF-I axis thus commends itself to more formalized modeling (154, 155), since the multivalent feedback-control activities are difficult to assimilate fully on an intuitive scale. Understanding the dynamic neuroendocrine mechanisms that direct the pulsatile secretion of this fundamental growth-promoting and metabolic hormone remains a critical goal, the realization of which is challenged by the exponentially accumulating matrix of experimental and clinical data in this arena. To the above end, we review here the pathophysiology of the GHRH somatostatin-GH-IGF-I feedback axis consisting of corresponding key neurotransmitters, neuromodulators, and metabolic effectors, and their cloned receptors and signaling pathways. We propose that this system is best viewed as a multivalent feedback network that is exquisitely sensitive to an array of neuroregulators and environmental stressors and genetic restraints. Feedback and feedforward mechanisms acting within the intact somatotropic axis mediate homeostatic control throughout the human lifetime and are disrupted in disease. Novel effectors of the GH axis, such as GHRPs, also offer promise as investigative probes and possible therapeutic agents. Further understanding of the mechanisms of GH neuroregulation will likely allow development of progressively more specific molecular and clinical tools for the diagnosis and treatment of various conditions in which GH secretion is regulated abnormally. Thus, we predict that unexpected and enriching insights in the domain of the neuroendocrine pathophysiology of the GH axis are likely be achieved in the succeeding decades of basic and clinical research.

Role, sensitivity and validity of GH stimulation tests in the diagnosis of growth hormone deficiency in adults

This study was conducted to evaluate whether stimulated concentrations of growth hormone (GH) are of practical use in establishing the diagnosis of acquired GH deficiency. The secretion of GH as stimulated by GH releasing hormone (GHRH; 100 microg i.v.) was studied in 33 patients with non-functioning pituitary macroadenomas prior to and after trans-sphenoidal adenomectomy, as well as in 25 non-selected subjects who had been referred for evaluation of various suspected non-pituitary diseases. Patients with pituitary macroadenomas, who needed substitution therapy for at least one additional pituitary hormone, presented with lower (P<0.05) GHRH-stimulated GH secretion (3.2 +/- 4.3 ng/ml) than the remaining patients with pituitary tumours (7.2 +/- 6.6 mg/ml). Both groups showed a marked overlap with the control group (7.1 +/- 5.5 ng/ml). Although GH stimulation tests are superior to other biochemical criteria of GH deficiency, they are still an inadequate method to reliably diagnose GH deficiency in an individual patient. In clinical practice GH replacement therapy should, therefore, only be considered if, in addition to impaired GH secretion, the patients present with additional defects in anterior pituitary function and clinical symptoms are compatible with a lack of GH.

How (not) to diagnose growth hormone deficiency in adults: stimulated serum concentrations of growth hormone in healthy subjects and in patients with pituitary macroadenomas

The secretion of growth hormone (GH) stimulated by GH-releasing hormone ([GHRH] 100 micrograms intravenously [IV]) was determined in 33 patients with nonfunctioning pituitary macroadenomas before and after transsphenoidal adenomectomy and in 28 controls. Patients who needed substitution therapy for at least one additional pituitary hormone presented with lower GH secretion than the remaining patients with pituitary tumors. However, there was a marked overlap of stimulated GH secretion between these two groups (3.2 +/- 4.3 ng/mL and 7.2 +/- 6.6 ng/mL, respectively) and between either group with the control group (7.1 +/- 5.5 ng/mL). In an independent investigation, the effect of IV GHRH (100 micrograms) on the secretion of GH in seven healthy volunteers was shown to be comparable to that seen during an insulin tolerance test ([ITT] 0.1 U/kg IV). Thus, the GHRH stimulation test, a simple and comparatively unharmful procedure, is a useful alternative to the ITT in patients with potential pituitary defects. However, the pronounced overlap of stimulated serum GH concentrations in patients with pituitary macroadenomas and those estimated in healthy subjects and in patients with nonpituitary diseases underlines the difficulty in biochemically defining acquired GH deficiency in adults. We suggest that GH therapy in adults should primarily be instituted in patients with additional defects in anterior pituitary function.

Effect of chronic administration of a new potent agonist of GH-RH(1-29)NH2 on linear growth and GH responsiveness in rats

The effects of a repeated or continuous administration of a potent agonistic analog of growth hormone-releasing hormone (GH-RH), [Dat1, Thr8, Orn12,21, Abu15, Nle27, Asp28, Agm29] hGH-RH(1-29)(JI-36), on the linear growth and the GH responses to bolus injections of GH-RH(1-29)NH2 were investigated in male rats about 7 weeks old. Body weight and tail length were monitored. Basal serum GH and IGF-I concentrations and GH responses to GH-RH(1-29)NH2 were measured by RIA. Chronic administration of GH-RH agonist JI-36 by continuous release from osmotic minipumps at the rate of 0.2 microgram/h or twice daily injections of 0.5 and 5 micrograms/rat for 4 weeks significantly speeded up the growth of rats as measured by the tail length. The acceleration of growth was similar in the 3 groups and was associated with stimulation of IGF-I secretion. The GH response to bolus injection of GH-RH(1-29)NH2 was preserved in all groups and no attentuation of the response occurred in rats treated for 4 weeks with agonist JI-36 as compared with the control group. Our results indicate that chronic administration of GH-RH agonist JI-36 significantly increases the growth rate without affecting somatotroph responsiveness in rats. It is therefore likely that this class of GH-RH agonists may be useful clinically.

The involvement of dipeptidyl peptidase IV in brush-border degradation of GRF(1-29)NH2 by intestinal mucosal cells

GRF(1-29)NH2 is degraded mainly by dipeptidyl peptidase IV (DPP IV) in plasma, resulting in inactivated GRF(3-29)NH2. To understand whether improving stability of GRF(1-29)NH2 in the plasma will result in enhanced stability in intestinal mucosal cells, stability of GRF(1-29)NH2 and [desNH2Tyr1,D-Ala2,Ala15]-GRF(1-29)NH2 in rat intestine brush-border membrane and homogenate was examined. [desNH2Tyr1,D-Ala2,Ala15]-GRF(1-29)NH2, resistant to plasma DPP IV, was much more stable than GRF(1-29)NH2 in enterocytes. Gradient HPLC analysis, mass balance analysis and studies of inhibitor effects revealed that GRF(3-29)NH2 was the major metabolite of GRF(1-29)NH2 due to the action of DPP IV during incubation with brush-border membranes. It is concluded that the design of peptide analogues to resist plasma enzymes dramatically increases stability in intestinal epithelium.

Rational design, synthesis, and biological evaluation of novel growth hormone releasing factor analogues

Since its initial discovery in 1982, growth hormone-releasing factor (GRF) has been the subject of intense investigation. This interest was prompted by the potential application of GRF for stimulating growth in dwarf humans and for performance enhancement in livestock. Substantial research has been focused upon the development of potent, long-acting analogs as therapeutics. Herein is described a summary of the cumulative efforts of various laboratories endeavoring in this quest. The rationale utilized in GRF analog development is discussed: 1) determination of bioactive core, 2) evaluation of secondary structure, and 3) elucidation of degradation pathways (chemical and enzymatic). Using this information, several series of linear (unnatural and natural sequence) and cyclic GRF analogs were designed, synthesized, and evaluated. Stimulated by the constraints of commercial production, innovative, alternative methods of synthesis were explored: solid-phase, solution-phase, enzymatic, and recombinant. To date, the most promising candidate for drug development is [His1, Val2, Gln8, Ala15, Leu27]-hGRF(1-32)-OH. This natural sequence analog, consisting of rodent and human sequences, incorporates the bioactive core, preferred secondary structure, resistance to chemical and enzymatic degradation; with the added benefit of amenability to large-scale recombinant synthesis.

Priming with GHRH (1-29) NH2: an aid in differential diagnosis between hypothalamic and pituitary deficiencies

More than 80% of children with growth hormone deficiency (GHD) respond with a rise in growth hormone levels when given 1 microgram/kg body weight of growth hormone-releasing hormone (GHRH) in an i.v. bolus. We conducted a study to determine whether the failure of the remaining 20% to respond to GHRH is due to a pituitary deficiency or a secondary effect associated with chronically understimulated somatotrophs. We administered GHRH to "prime" 16 short-statured children (> 2 SD) presenting delayed growth (< 4 cm/year), who had not responded initially when given a single dose of GHRH. Priming consisted of administering GHRH (1-29) NH2 (5 micrograms/kg body weight, s.c.) for six consecutive days. Plasma GH response was studied again after an i.v. injection of 1 microgram/kg body weight of GHRH (1-29) NH2 on the seventh morning. On the basis of these results we were able to separate our patients into two groups: a) responders to priming (n = 8), whose GH responses to pharmacological and acute GHRH tests were < 10 ng/ml, with a 12-hour sleep secretion < 3 ng/ml/min. Priming increased the plasma GH response to acute GHRH in all the children in this group (6.0 +/- 2.1 ng/ml to 18.0 +/- 5.4 ng/ml; p < 0.001); b) non-responders to priming (n = 8), whose GH responses to pharmacological and acute GHRH tests were also < 10 ng/ml, with 12-hour sleep secretion < 3 ng/ml/min, but in whom priming with GH did not increase the plasma GH response (5.5 +/- 2.8 ng/ml to 6.2 +/- 2.9 ng/ml; p = NS).(ABSTRACT TRUNCATED AT 250 WORDS)

Treatment with GHRH(1-29)NH2 in children with idiopathic short stature induces a sustained increase in growth velocity

OBJECTIVE

Therapy with GHRH in patients with mild GH insufficiency appears to be more effective than in those with severe insufficiency. We, therefore, studied the clinical response of children with idiopathic short stature to treatment with GHRH(1-29)NH2 (GHRHa) for a period of 12 months.

DESIGN

Eighteen short pre-pubertal children (aged 4.3-11.0 years, 17 male) with idiopathic short stature (height < 3rd centile, peak GH to provocative testing > 20 mU/l) were recruited to receive GHRHa 20 micrograms/kg by twice daily s.c. injection for one year. One patient was non-compliant and was withdrawn prior to 3 months of therapy. Pretreatment height velocity was calculated for 12 months and subjects were measured 3-monthly during therapy. Overnight GH profiles and s.c. GHRH tests (20 micrograms/kg) were performed at 0, 3, 6 and 12 months of therapy. In addition, an i.v. GHRH test (1 microgram/kg) was performed at the start and after 1 month of therapy.

MEASUREMENTS

Overnight GH profiles were analysed using the Pulsar program.

RESULTS

Mean (SD) height velocity (HV) increased from 4.8(0.9)cm/year pre-treatment to 7.2(1.6)cm/year after 12 months of therapy (P = 0.001). The children growing slowly (HV < 25th centile) before treatment had a greater growth response than those growing normally (HV > or = 25th centile) before treatment. Final height prediction increased by a mean (SD) of 3.4(2.6)cm. Overnight GH levels and GH responses to GHRH testing fell during the 12 months of therapy. Fasting blood glucose and insulin levels increased during therapy, as did IGF-I. Cessation of GHRHa was followed by catch-down growth during the first 3 months off therapy: mean (SD) HV 3.89(1.82)cm/year (P < 0.04), although the HV after 6 months (4.9(1.0))cm/year) and 12 months (4.4(1.0)cm/year) was not different from pretreatment values.

CONCLUSIONS

Short-term therapy with twice-daily s.c. injection of GHRHa (20 micrograms/kg) promoted linear growth in short children who were not GH-insufficient. The improved height velocity was sustained throughout the 12 months of treatment, followed by catch-down growth, and returned to pretreatment velocity after cessation of therapy.

New Gaba-containing analogues of human growth hormone releasing hormone (1-30)-amide: II. Detailed in vivo biological examinations

Analogues of human growth hormone-releasing hormone-(1-30)-amide [GH-RH(1-30)-amide] were tested for their ability to stimulate GH release in vivo by injecting the peptides intravenously (iv), subcutaneously (sc), and intramuscularly (im). The analogues involved derivatization with Nle27 and Gaba substituents at the C-terminus with or without D-amino acid(s) in the peptide chain. The potency of the analogues was compared to that of GH-RH(1-29)-amid testing their ability to release GH at 5, 15 and 30 min after the administration. In iv test the potency of the analogues was 1.2-2 times higher than that of the GH-RH(1-29)-amide, and no significant differences were detected between the potencies of the analogues with or without D-amino acid. In the sc test the analogue with D-Ala2, Nle27, and Gaba30 substitutions expressed 8.0-51.7 times higher potency than the GH-RH(1-29)-amide, however, the analogue with similar modifications but with L-Ala2 showed the same low potency (1.2-2.1) as in the iv test. Results from the im experiments were similar to those of SC test. The most potent analogues were those which had D-Ala2, Nle27, and Gaba30 substitutions with Gly15 or Leu15. Circular dichroism (CD) spectra of the analogues showed that Leu in position 15 increased the stability of the predominant alpha-helix conformation, which improved the absorption of the molecule.(ABSTRACT TRUNCATED AT 250 WORDS)

Comparison of GH-stimulation by GH-RH(1-29)NH2 and an agmatine29 GH-RH analog, after intravenous, subcutaneous and intranasal administration and after pulmonary inhalation in rats

Many studies have shown that human GH-RH(1-29)NH2 possesses full intrinsic activity of GH-RH(1-44)NH2 in vitro and in vivo. This investigation was performed to evaluate the efficacy of GH-RH(1-29)NH2 given by different routes of administration in stimulating GH release in rats. In each case GH-RH(1-29)NH2 was administered intravenously, subcutaneously, intranasally and by pulmonary inhalation at two different doses to groups of seven males rats. At a dose of 150 micrograms/kg GH-RH(1-29)NH2, the magnitude of GH response was significantly higher for the pulmonary inhalation group (355 +/- 33.2 ng GH/mL) than for the subcutaneous group (246 +/- 36 ng GH/mL) or for the intranasal group (175 +/- 30 ng GH/mL). The group injected intravenously with GH-RH(1-29)NH2 at a dose of 2.5 micrograms/kg showed the highest response, GH levels reaching 877.2 +/- 115 ng/mL. A similar pattern of responses was obtained for the superactive GH-RH(1-29) agmatine29 analog, MZ-3-149, at doses that were 50 times lower. Our results indicate a high bioavailability of GH-RH(1-29)NH2 or analog MZ-3-149 administered by a convenient pulmonary inhalation route. The GH-releasing effect of GH-RH(1-29)NH2 or analog MZ-3-149 delivered by pulmonary inhalation is superior to subcutaneous and intranasal administration.

Pharmacokinetics of growth hormone-releasing hormone(1-29)-NH2 and stimulation of growth hormone secretion in healthy subjects after intravenous or intranasal administration

The growth hormone-releasing hormone analogue GHRH(1-29)-NH2 was administered intravenously or intranasally to 30 healthy men aged 19-43 years. Intravenous injection of the lowest dose tested, 0.25 microgram/kg body weight, elicited significant release of growth hormone (GH). Maximal release (mean GH peaks of about 90 mU/l) was obtained with a dose of 1-2 micrograms/kg. Although GHRH(1-29)-NH2 was rapidly eliminated after intravenous injection, GH levels were elevated for about 3 hours. Absorption of GHRH(1-29)-NH2 through the nasal mucosa was found to be low, and the bioavailability was only 3-5%. There was a dose-dependent release of GH after intranasal administration of GHRH(1-29)-NH2, with the maximal response obtained with about 50 micrograms/kg; this dose was approximately as potent as 1 microgram/kg injected intravenously. The GH response after repeated intranasal administration of GHRH(1-29)-NH2 was sustained; there was no suppression of GH secretion during the night following a day when GHRH(1-29)-NH2 had been given three times intranasally. Based on these findings and the obvious convenience of intranasal administration compared with injections, it would be justified to test intranasal therapy for treatment of short stature in children with GH deficiency caused by hypothalamic damage.

Growth response to growth hormone-releasing hormone(1-29)-NH2 compared with growth hormone

To assess the growth-promoting effect of different doses of growth hormone-releasing hormone(1-29)-NH2 (GHRH(1-29)-NH2) in GH deficiency (GHD) of hypothalamic origin, 43 prepubertal children aged between 4.3 and 18.9 years (mean 10.4 +/- 2.9 years) were randomly assigned to three treatment regimens: low-dose GHRH(1-29)-NH2 (LD group; n = 15), high-dose GHRH(1-29)-NH2 (HD group; n = 12) and GH (GH group; n = 16). The LD group received GHRH(1-29)-NH2 at 30 micrograms/kg/day s.c. in three daily doses, the HD group received 60 micrograms/kg/day s.c. in three daily doses and the GH group received GH, 0.1 IU/kg/day s.c. once daily. All children were treated for a period of 6 months. Evaluation included anthropometry, bone age, intravenous and subcutaneous GHRH(1-29)-NH2 tests and determination of insulin-like growth factor I (IGF-I) levels. An increase in height velocity of 2 cm/year or more was observed in all except two children. Height velocity during treatment was lowest in the LD group, but comparable in the HD and GH groups. An increase in height SDS for bone age occurred only in the GH-treated group. GH responses to intravenous GHRH(1-29)-NH2 showed a priming effect of the LD GHRH(1-29)-NH2 treatment, while a decrease in response occurred in the GH-treated group. Following a subcutaneous test dose of one-third of the daily dose of GHRH(1-29)-NH2, GH levels remained unchanged in both the LD and HD groups. There was accumulation of GHRH immunoreactivity over time in the HD group, but there was no correlation between measured GHRH and GH levels.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of nightly clonidine administration on growth velocity in short children without growth hormone deficiency: a double-blind, placebo-controlled study

Children with short stature, slowed linear growth velocity, and delayed skeletal maturation may secrete growth hormone (GH) normally in response to provocative stimuli but may also have spontaneous undersecretion of GH. Orally administered clonidine, an alpha 2-adrenergic agonist, is a potent acute stimulator of growth hormone releasing hormone-mediated pituitary GH release. We performed a double-blind, placebo-controlled crossover study of nightly oral clonidine therapy (0.1 mg/m2) in 10 short, slowly growing, non-GH-deficient (stimulated GH level > 15 micrograms/L) prepubertal boys (range, 6.1 to 12.2 years; mean height standard deviation score, -2.3 +/- 0.4). Results of 6 months of clonidine therapy were compared with the results of 6 months of placebo therapy; GH responsiveness was subsequently assessed in 7 of 10 patients. Growth velocity (4.9 +/- 0.6 cm/yr baseline) was not improved by clonidine (4.6 +/- 1.2 cm/yr) or placebo (5.2 +/- 1.2 cm/yr), but it increased (p < 0.001) with GH therapy (8.2 +/- 1.3 cm/yr). Clonidine therapy similarly did not significantly affect plasma levels of insulin-like growth factor I or bone age maturation. Diminution in clonidine-stimulated peak GH levels was not observed after long-term oral clonidine therapy. Thus, in contrast to previous non-placebo-controlled studies, nightly clonidine therapy did not increase growth velocity or plasma insulin-like growth factor I levels. Subsequent acceleration in growth velocity during GH therapy suggests that a proposed increase in clonidine-induced endogenous GH secretion does not result in an effective growth-promoting stimulus.

Potent agonists of growth hormone-releasing hormone. Part I

Analogs of the 29 amino acid sequence of growth hormone-releasing hormone (GH-RH) with agmatine (Agm) in position 29 have been synthesized by the solid phase method, purified, and tested in vitro and in vivo. The majority of the analogs contained desaminotyrosine (Dat) in position 1, but a few of them had Tyr1, or N-MeTyr1. Some peptides contained one or more additional L- or D-amino acid substitutions in positions 2, 12, 15, 21, 27, and/or 28. Compared to the natural sequence of GH-RH(1-29)NH2, [Dat1,Ala15]GH-RH(1-28)Agm (MZ-3-191) and [D-Ala2,Ala15]GH-RH(1-28)Agm (MZ-3-201) were 8.2 and 7.1 times more potent in vitro, respectively. These two peptides contained Met27. Their Nle27 analogs, [Dat1,Ala15,Nle27]GH-RH(1-28)Agm(MZ-2-51), prepared previously (9), and [D-Ala2,Ala15,Nle28]GH-RH(1-28)Agm(MZ-3-195) showed relative in vitro potencies of 10.5 and 2.4, respectively. These data indicate that replacement of Met27 by Nle27 enhanced the GH-releasing activity of the analog when the molecule contained Dat1-Ala2 residues at the N-terminus, but peptides containing Tyr1-D-Ala2 in addition to Nle27 showed decreased potencies. Replacement of Ser28 with Asp in multi-substituted analogs of GH-RH(1-28)Agm resulted in a decrease in in vitro potencies compared to the parent compound. Thus, the Ser28-containing MZ-2-51, and [Dat1,Ala15,D-Lys21,Nle27]GH-RH(1-28)Agm, its Asp28 homolog (MZ-3-149), possessed relative activities of 10.5 and 5.6, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Pyridostigmine fails to increase either spontaneous or GHRH-stimulated GH secretion during day or night in growth hormone-insufficient children

OBJECTIVE The aim of the study was to investigate whether pyridostigmine, a cholinesterase inhibitor which is thought to act at the hypothalamus to inhibit somatostatin secretion, would augment spontaneous or GHRH-stimulated serum GH levels in patients with GH-insufficiency. DESIGN Oral pyridostigmine 60 mg or placebo was administered at the start of a 9-h subcutaneous infusion of either GHRH (1-29)NH2 10 micrograms/kg/h or saline control. Studies were performed during the daytime (0900-1800 h) in five patients, and the night-time (2100-0600 h) in a further five. PATIENTS Ten short, pre-pubertal children (aged 6-11 years; eight boys) with growth hormone insufficiency were studied. MEASURES Blood for serum GH was sampled every 20 min, and analysed using the PULSAR program. RESULTS The subcutaneous infusion of GHRH 10 micrograms/kg/h increased mean serum GH levels (+/- SEM): by day 17.7(+/- 6.8) vs placebo 2.2(+/- 0.4) mU/l (P less than 0.01), and by night 26.9(+/- 3.3) vs 5.5(+/- 1.3) mU/l (P less than 0.05). There was a significant rise in mean 'baseline' GH concentration: by day 5.5(+/- 1.7) vs 1.0(+/- 0.0) mU/l (P less than 0.05); and night 8.2(+/- 2.7) vs 1.3(+/- 0.3) mU/l (P less than 0.05). Pyridostigmine failed to produce a significant overall increase in either spontaneous or GHRH-stimulated GH secretion by day or night, although there was a significant rise in mean GH levels during the 3 h following pyridostigmine administration in the morning: 4.4(+/- 1.1) vs 2.4(+/- 0.5) mU/l (P less than 0.001). GHRH or pyridostigmine given singly or in combination had no significant effect on the number of pulses. Side-effects attributable to pyridostigmine occurred in seven children. CONCLUSIONS Pyridostigmine, either on its own or as an adjuvant therapy in combination with GHRH, acts for only a brief time and does not offer any potential benefit in the management of children with short stature.

The role of cholinergic tone in modulating the growth hormone response to growth hormone-releasing hormone in normal man

Growth hormone-releasing hormone (GHRH) increases serum GH levels in a dose-dependent manner. Pyridostigmine (PD), an acetylcholinesterase inhibitor, is able to elicit GH secretion when administered alone and to enhance the GH response to GHRH in normal subjects, probably via a decrease in the hypothalamic release of somatostatin. The aim of the present study was to investigate if an enhancement of the cholinergic tone was able to influence the dose-response relationship between GHRH and GH in normal adult subjects. Six healthy adult volunteers underwent 10 experimental protocols. They were: human GHRH (1-29)NH2, 1 micrograms/kg injected as an intravenous (IV) bolus 60 minutes after (a) PD, 120 mg administered orally, or (b) placebo, two tablets administered orally; GHRH, 0.3 micrograms/kg injected as an IV bolus 60 minutes after (c) PD or (d) placebo; GHRH, 0.1 micrograms/kg injected as an IV bolus 60 minutes after (e) PD or (f) placebo; GHRH, 0.01 micrograms/kg injected as an IV bolus 60 minutes after (g) PD or (h) placebo; saline, 1 mL injected as an IV bolus 60 minutes after (i) PD or (l) placebo. The GH response in placebo-treated subjects was similar after 1 microgram/kg and 0.3 microgram/kg GHRH, while the 0.1 microgram/kg dose elicited a lower response. The 0.01 microgram/kg dose of GHRH did not significantly increase GH levels as compared with saline. After PD, the GH responses to GHRH were greatly enhanced at all doses tested: 1.0, 0.3, and 0.1 microgram/kg GHRH all elicited similar GH responses; the GH response to 0.01 microgram/kg GHRH was lower, but was still higher than that observed after saline.(ABSTRACT TRUNCATED AT 250 WORDS)

Evaluation of in vivo [corrected] biological activity of new agmatine analogs of growth hormone-releasing hormone (GH-RH)

The effects of agmatine analogs of growth hormone releasing hormone (GH-RH) were compared to GH-RH(1-29)-NH2 after intravenous (iv) and subcutaneous (sc) administration to pentobarbital-anesthetized male rats. After the iv injection, the analogs [desNH2-Tyr1,Ala15,Nle27] GH-RH(1-28)Agm (MZ-2-51); [desNH2-Tyr1,D-Lys12,Ala15,Nle27] GH-RH(1-28)Agm (MZ-2-57); [desNH2-Tyr1,Ala15,D-Lys21,Nle27] GH-RH(1-28)Agm (MZ-2-75) and [desNH2-Tyr1, D-Lys12,21, Ala15, Nle27] GH-RH(1-28)Agm (MZ-2-87) showed a potency equivalent to 4.4, 1.9, 1.07 and 1.03 times that of GH-RH (1-29)-NH2, respectively, at 5 min and 5.6, 1.8, 1.9 and 1.8 times higher, respectively, at 15 min. After sc administration, analogs MZ-2-51, MZ-2-57 and MZ-2-75 showed to be 34.3, 14.3 and 10.5 times more potent than the parent hormone at 15 min and 179.1, 88.9 and 45.0 times more active, respectively, at 30 min. In addition, MZ-2-51 had prolonged GH-releasing activity as compared to the standard. We also compared the activity of MZ-2-51 and MZ-2-57 with their homologous L-Arg and D-Arg analogs [desNH2-Tyr1,Ala15,Nle27] GH-RH(1-29)-NH2 (MZ-2-117), [des-NH2Tyr1,D-Lys12, Ala15, Nle27] GH-RH(1-29)NH2 (MZ-2-123) and [desNH2-Tyr1,D-Lys12,Ala15, Nle27,D-Arg29] GH-RH(1-29)NH2 (MZ-2-135) after intramuscular (im) injection. MZ-2-51 induced a somewhat greater GH release than MZ-2-117 at 15 min, both responses being larger than the controls (p less than 0.01) at 15 and 30 min. MZ-2-57, MZ-2-123 and MZ-2-135 given i.m. were able to stimulate GH release only at 15 minutes (p less than 0.05). Animals injected i.m. with MZ-2-51, but not with MZ-2-117, showed GH levels significantly higher than the control group (p less than 0.05) at 60 min. GH-RH(1-29)NH2 had low activity intramuscularly when tested at a dose of 2.5 micrograms. No toxic effects were observed after the iv administration of 1 mg/kg of Agm GH-RH analogs. These results indicate that our Agm analogs are active iv, sc and im and that the substitutions made in these compounds produce increased and prolonged GH releasing activity. These analogs, especially MZ-2-51, should be useful for clinical and veterinary purposes.

Effects of intranasal calcitonin administration on pituitary GH response to hGHRH (1-29)NH2 in normal adult subjects

Studies in man demonstrated that intramuscular salmon (s) calcitonin (CT) administration blunted pituitary GH response to hypothalamic stimuli such as arginine infusion and insulin-induced hypoglycaemia. However, the mechanisms underlying this inhibiting action of CT are still unclear. The aim of our study was to investigate the effects of intranasal (i.n.) and i.m. sCT administration on GH secretion elicited by direct pituitary stimulation in man with human GH-releasing hormone (GHRH) (1-29)NH2. Seven healthy non-obese volunteers (five men, two women; mean age +/- SDM 25 +/- 2) underwent a bolus intravenous injection of GHRH, 100 micrograms, alone or associated with sCT, administered either i.n., 300 IU, or i.m., 100 IU. Our data demonstrate a significant decrease in GH secretion after GHRH when either i.n. or i.m. sCT is administered. GH peak (mean +/- SDM); GHRH alone 22.9 +/- 2.5 vs GHRH plus i.n. sCT, 8.9 +/- 1.5 micrograms/l, P less than 0.001; or vs GHRH plus i.m. sCT 12.3 +/- 2.5 micrograms/l, P less than 0.001. Area under the curve of GH secretion: GHRH alone 1211 +/- 196 vs GHRH plus i.n. sCT 551 +/- 116 micrograms 120 min/l. P less than 0.001; or vs GHRH plus i.m. sCT 700 +/- 167 micrograms 120 min/l, P less than 0.001. We conclude that sCT is able to inhibit GHRH-stimulated GH secretion in man.

Reasons for the variability in growth hormone (GH) responses to GHRH challenge: the endogenous hypothalamic-somatotroph rhythm (HSR)

The aims of this study were: (1) to test the possibility that pre-GHRH plasma GH values could reflect the functional status of the hypothalamic-somatotroph rhythm (HSR) at testing, and thus explain if it is responsible for the marked variability in GH responsiveness to GHRH challenge and (2) to see if exogenous somatostatin (SS) could disrupt this endogenous HSR and thus make the GH responses homogeneous. (1) Two to 14 GHRH acute tests (GRF-29, 1 micrograms/kg, i.v. bolus) were performed in 12 normal men and 10 normal women at the same time (0830 h) at random intervals (2 to 60 days). Blood samples to measure plasma GH were drawn at 15 min intervals before and after GHRH challenge. Given that the increments in pre-GHRH plasma GH values (I = value at 0 min minus value at -15 min) were highly correlated with either GHRH-elicited peaks of GH (men, r = 0.81; women; r = 0.69; P less than 0.0001) or the rise in GH after the challenge (r = 0.685; P less than 0.0001, in the total of tests performed), three theoretical HSR phases were proposed: (A) I greater than or equal to 0.4 microgram/l Secretory Phase; (B) I less than or equal to 0, (from GH at -15 min greater than or equal to 1.5 microgram/l), Secretion Plateau; (C) I less than or equal to 0, (from GH at -15 min less than or equal to 1.5 microgram/l), Refractory Phase. Individually, 91% of the men and 86% of the women showed a constant HSR phase when tested at the same time of day independently of the intervals between tests. GH responses (peaks, mean +/- SEM, g/l) in Phase A (women, 51.5 +/- 4.1; men, 31.4 +/- 3.2) were significantly higher (P less than 0.01) than those in Phase B (women, 22.6 +/- 1.8; men, 19.7 +/- 1.5), and these than those in Phase C (women, 9.2 +/- 1.5; men, 6.2 +/- 0.5). The great dispersion observed when GH peaks were analysed as a whole disappeared (except in Phase A in women) when they were evaluated according to the HSR Phase at testing. (2) In seven men and eight women 7 min after stopping an infusion of SS (250 micrograms/h for 3 h) a new GHRH test was performed. Plasma GH variations prior to SS infusion expressed the previous HSR Phase, while the GHRH-elicited peak of GH established the Phase at the moment of testing.(ABSTRACT TRUNCATED AT 400 WORDS)

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 micrograms/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.

Bioactivity of growth hormone releasing hormone (1-29) analogues after SC injection in man

The bioactivity of growth hormone releasing hormone 1-29 [GHRH(1-29)NH2] has been compared with that of an agonist analogue [Ac-D-Tyr1,D-Ala2]-GHRH(1-29)NH2, in normal male volunteers. Using a submaximal dose of 3 micrograms/kg administered subcutaneously, peak growth hormone (GH) response and area under the GH curve were similar for the native and agonist analogue. In addition, no significant differences were found in peak GHRH(1-29) immunoreactivity, area under the GHRH(1-29) curves or plasma disappearance rates of the two peptides. The results suggest that, in keeping with the relative activities of other "superactive" analogues tested so far, the greatly enhanced activity of [Ac-D-Tyr1,D-Ala2]-GHRH(1-29)NH2 observed in the rat is not found in humans. It is possible that this species difference is due to differences in the interaction of GHRH peptides with the rat and the human somatotroph GHRH receptor.

Synthesis, biological activity and conformational analysis of cyclic GRF analogs

A novel cyclic GRF analog, cyclo(Asp8-Lys12)-[Asp8,Ala15]-GRF(1-29)-NH2, i.e. cyclo8,12[Asp8,Ala15]-GRF(1-29)-NH2, was synthesized by the solid phase procedure and found to retain significant biological activity. Solid phase cyclization of Asp8 to Lys12 proceeded rapidly (approximately 2 h) using the BOP reagent. Substitution of Ala2 with D-Ala2 and/or NH2-terminal replacement (desNH2-Tyr1 or N-MeTyr1) in the cyclo8,12[Asp8,Ala15]-GRF(1-29)-NH2 system resulted in highly potent analogs that were also active in vivo. Conformational analysis (circular dichroism and molecular dynamics calculations based on NOE-derived distance constraints) demonstrated that cyclo8,12[Asp8,Ala15]-GRF(1-29)-NH2 contains a long alpha-helical segment even in aqueous solution. A series of cyclo8,12 stereoisomers containing D-Asp8 and/or D-Lys12 were prepared and also found to be highly potent and to retain significant alpha-helical conformation. The high biological activity of cyclo8,12[N-MeTyr1,D-Ala2,Asp8,Ala15]-GRF(1-29)- NH2 may be explained on the basis of retention of a preferred bioactive conformation.

Growth hormone releasing hormone or growth hormone treatment in growth hormone insufficiency?

Sixteen prepubertal children who were insufficient for growth hormone were treated with growth hormone releasing hormone (GHRH) 1-40 and GHRH 1-29 for a mean time of nine months (range 6-12 months) with each peptide. Eleven children received GHRH 1-40 in four subcutaneous nocturnal pulses (dose 4-8 micrograms/kg/day) and eight (three of whom were also treated with GHRH 1-40) received GHRH 1-29 twice daily (dose 8-16 micrograms/kg/day). Altogether 73% of the children receiving GHRH 1-40 and 63% receiving GHRH 1-29 showed a growth response. Double the daily dose of GHRH 1-29 was required to obtain equivalent growth response to pulsatile GHRH 1-40. A significant linear correlation was shown between growth hormone secretion and height velocity on GHRH 1-40 but not on GHRH 1-29 and there was a significant correlation between plasma GHRH and serum growth hormone concentrations during GHRH 1-40 administration. Response to conventional growth hormone treatment in a matched group of children was significantly better than the response after GHRH. A significant improvement in height velocity was observed in the children transferred to growth hormone replacement. Growth hormone remains the treatment of choice in growth hormone insufficiency. GHRH treatment may be of benefit in children with less severe growth hormone insufficiency in the presence of pulsatile endogenous growth hormone secretion.

Expression in Escherichia coli and characterization of human growth-hormone-releasing factor

A chemically synthesized DNA sequence, coding for the 44 amino acid residues of human growth-hormone-releasing factor (GRF) preceded by a tryptophan codon, was cloned in frame with Escherichia coli trpE gene within a pBR322-derived plasmid. GRF was expressed in E. coli as a fused polypeptide chain (TrpE-GRF) and then the GRF amino acid sequence was released from the fused protein by specific chemical cleavage at the tryptophan residue using o-iodosobenzoic acid. The thioether group of the methionine residue of GRF was converted in the sulfonium salt derivative, in order to prevent irreversible oxidation of methionine to the sulfone derivative by the o-iodosobenzoic acid reagent. GRF was purified by HPLC and characterized in terms of amino acid composition after acid hydrolysis, protein sequencing and gel electrophoretic behaviour. These data clearly established that the biosynthetic GRF was identical to the natural one, except for the lack of amidation at the carboxyl-terminal amino acid. Far-ultraviolet circular dichroism measurements established that both biosynthetic and natural GRF are devoid of secondary structure in aqueous solution at neutral pH, whereas both peptide samples achieve a high percentage of helical structure in the presence of trifluoroethanol.

An evaluation of intravenous, subcutaneous, and in vitro activity of new agmatine analogs of growth hormone-releasing hormone hGH-RH (1-29)NH2

The effects of new Agmatine (Agm) analogs of human growth hormone-releasing hormone (GH-RH) were compared to GH-RH (1-29)NH2 and to (D-Ala2)GH-RH(1-29)NH2 after intravenous (IV) and subcutaneous (SC) administration to pentobarbital-anesthetised male rats and in vitro using superfused rat pituitary cell system. After IV administration, the analogs: (D-MeAla2,Nle27)GH-RH(1-28)Agm(JG-75), (desamino-Tyr1,D-Ala2,Nle27)GH-RH(1-28)Agm(JG-77), (D-Ala2,Nle27)GH-RH(1-28)Agm(JG-73) and (D-Ala2)GH-RH(1-29)NH2 showed a potency 2.6-3.9 times greater than GH-RH(1-29)NH2 at 5 min and 1.6-2.7 times higher at 15 min. After SC administration these analogs were 30-74 times more potent than GH-RH(1-29)NH2. The ratio between the IV and SC GH-releasing activity of the analogs ranged from 2 to 5, while GH-RH(1-29)NH2 was about 50 times more active IV than SC. This indicates that 20-50% of the analogs can be absorbed from SC tissues, but only 2% of GH-RH(1-29)NH2. The in vitro activity of the agmatine analogs on GH release closely paralleled their IV potency and was 2.8-3.9 times greater than that of GH-RH(1-29)NH2. No significant difference in potency was found between (D-Ala2)GH-RH(1-29)NH2 and JG-75 after IV administration and in vitro, although JG-75 contained only 28 amino acids. We conclude that the reason for the large discrepancies between the previously reported activities of (D-Ala2)GH-RH(1-29)NH2 was simply due to the different ways of administration of this analog, SC vs IV, and not to species specificity. The replacement of Arg29 by Agmatine in (D-Ala2,Nle27)GH-RH(1-29)NH2 causes a 3 fold increase in SC potency, but the replacement of D-Ala2 with D-MeAla2 reduces the SC, but not the IV and in vitro activity in half.

Pharmacokinetic evaluation of superactive analogues of growth hormone-releasing factor (1-29)-amide

D-amino acid-substituted analogues of growth hormone-releasing factor 1-29)-amide with superagonist activities in the rat were examined for increased plasma half-life and resistance to degradation in vivo. After IV injection, half-lives of the analogues were in the range 4.7-7.4 min, none of which was significantly different from that of the parent compound (6.2 min). Following SC injection, 4.6-7.2% of the dose of the analogues reached the circulation compared with 5.1% of the parent compound. Conformational restraints introduced into the N-terminal region of the molecule, which gave enhanced potency, did not alter the susceptibility of the peptide to proteolytic degradation.

Growth hormone response to growth hormone releasing factor in diabetic men

Increased plasma concentrations of growth hormone (GH) are reported in diabetes and it is suggested that this may be important in the development of complications. We have investigated fasting GH levels and the response to 100 micrograms i.v. growth hormone releasing factor, GRF(1-29)NH2, in age-matched men: six normal weight controls, six obese controls, six insulin-dependent diabetics, six normal weight non-insulin dependent diabetics and six obese non-insulin dependent diabetics. None of the diabetic men had clinical evidence of diabetic complications. Fasting GH values did not differ significantly between the five groups. The peak GH response to GRF was similar in the controls, insulin-dependent diabetics (IDD) and non-insulin dependent (NIDD) normal weight diabetics (mean peak +/- SEM: controls 25.5 +/- 5 mU/l, IDD 26.5 +/- 6 mU/l, NIDD 19.7 +/- 5 mU/l) but was significantly reduced in the two obese groups (obese 6.4 +/- 3 mU/l, obese diabetics 4.5 +/- 1 mU/l, P less than 0.01). This impairment of GH secretion was unrelated to either fasting plasma insulin or glucose concentration. We conclude that our results do not confirm the previous reports of abnormal GH secretion in diabetes but do demonstrate a markedly impaired GH response to GRF to be a feature of obesity.

GH feedback occurs through modulation of hypothalamic somatostatin under cholinergic control: studies with pyridostigmine and GHRH

We have studied the effect of increased cholinergic tone on the GH response to growth hormone-releasing hormone (GHRH) and on GH feedback, using pyridostigmine, an acetylcholinesterase inhibitor. In six healthy male adult volunteers 120 mg oral pyridostigmine increased basal GH secretion compared to placebo and augmented the GH response to 100 micrograms i.v. GHRH (1-29) NH2; the effect was more than the additive effect of pyridostigmine and GHRH when each was given alone. Pretreatment with 2 IU methionyl-hGH given i.v. abolished the serum GH response to GHRH given 3 h later, demonstrating a negative feedback loop of GH on the response to GHRH; this inhibited response to GHRH was restored in subjects given pyridostigmine as well as methionyl-hGH. The data demonstrate that enhanced cholinergic tone releases GH, augments the serum GH response to GHRH and unblocks the negative feedback effect of methionyl-hGH pretreatment on the GH response to GHRH. These results suggest that GH negative feedback effects on its own secretion occur predominantly through increased hypothalamic somatostatin secretion; this somatostatin secretion is under inhibitory cholinergic control.

Stilboestrol pretreatment of children with short stature does not affect the growth hormone response to growth hormone-releasing hormone

Oestrogens are known to enhance both basal and stimulated GH secretion. To examine whether this effect is mediated through the hypothalamus or the pituitary we performed insulin tolerance and GH-releasing hormone (GHRH) tests with and without oestrogen priming in a group of 14 short children. Pretreatment with stilboestrol increased basal levels of GH and both peak and incremental levels during insulin hypoglycaemia. In contrast, there was no effect of stilboestrol priming on the GH response to either an i.v. bolus of 100 micrograms or 0.1 microgram/kg (range 2-6 microgram) of GHRH. The children had significantly higher GH responses to an unprimed GHRH than unprimed insulin tolerance test. We conclude stilboestrol priming acts through the hypothalamus presumably by increasing endogenous GHRH release, and that short children with a subnormal GH response to insulin hypoglycaemia show a greater response to GHRH; this suggests the presence of a hypothalamic cause for their decreased GH secretion.

The place of intravenous GHRH 1-40 studies in the therapy of growth hormone-deficient children with GHRH

We studied GH responses to i.v. GH releasing hormone (GHRH) (1 microgram/kg) before and during the treatment of 11 GH deficient children with s.c. nocturnal pulsatile GHRH 1-40; seven for 9 months and four for 6 months. Each subject demonstrated GH stimulation at each i.v. study. There was a wide variation of response between subjects and in each subject on different occasions. Significant growth acceleration following s.c. GHRH was demonstrated in eight of 11 patients (73%). The sensitivity or true positive rate of the index GHRH study to predict a clinical response to s.c. treatment, regardless of the GH response achieved, was also 73%. When an index GH 'cut-off' response of less than 10 mU/l was employed, the probability of an increase in growth rate to s.c. GHRH fell to 0.50 (sensitivity 80%). The GHRH study was unhelpful, and in fact misleading, when assessed as a method of monitoring clinical progress and the outcome of pulsatile s.c. GHRH treatment. The growth response of a child to s.c. GHRH therapy is of far greater importance than the GH response following an i.v. bolus of GHRH. The index study gave no useful indication of either the potential GH pituitary reserve or which subjects would respond to treatment. Pretreatment and repeated GHRH studies are of limited value and should be interpreted with caution.

Effect of long-term administration of an analog of growth hormone-releasing factor on the GH response in rats

The effect of the repeated or continuous administration of an analog of GH releasing factor (GH-RF), D-Tyr-1, D-Ala-2, Nle-27, GH-RF(1-29)-NH2 (DBO-29), on the subsequent response to this peptide was investigated in pentobarbital-anesthetized male rats. A sc administration of this analog induced a greater and more prolonged GH release than doses 10 times larger of GH-RF(1-29). The GH increase after sc injection of 10 micrograms/kg bw of the analog was greater than that induced by iv administration of 2 micrograms/kg bw of GH-RF(1-44). Pretreatment with 10 micrograms/kg bw of the analog did not affect the pituitary response to a strong stimulus (20 micrograms/kg bw) of GH-RF(1-44), 24 h later. Pretreatment with the analog in doses of 10 micrograms/kg bw, sc twice a day, 5 days per week for 4 weeks, significantly diminished the GH release in response to a sc injection of the analog (10 micrograms/kg bw), as compared to vehicle-pretreated controls (P less than 0.01). On the other hand, a continuous sc administration of 0.4 micrograms/h of the analog to intact rats for 7 days did not result in a decrease in GH response to a sc injection of the analog (10 micrograms/kg bw). Since the rats injected repeatedly with the analog for 4 weeks still showed a marked, although somewhat reduced response, analogs of this type may be useful clinically.

Clonidine treatment for short stature

34 pubertal children with constitutional growth delay (CGD) were treated with clonidine orally twice a day. In 25 of the children the height velocity rose on clonidine treatment, and in 21 of them by more than 2 cm/yr during the first 6 months of treatment (mean [SD] growth increment 4.4 [0.5] cm/yr). Of the 22 who were treated for 12 months the increment in height velocity was maintained in 13 (3.4[0.4] cm/yr). Withdrawal of clonidine for 6 months did not stop the stimulatory effect of the drug on linear growth in 6 children, but in the other 8 children height velocities fell to pretreatment levels or below. In a few children reinstitution of clonidine for 2-4 months resulted in a new increment in height velocity. A high height standard deviation score and low growth velocity before treatment were predictive of a good growth response to clonidine. Clonidine did not induce noticeable side-effects. It may be a useful form of therapy for children with CGD.

The GH-releasing hormone (GHRH) test in acromegaly before and after adenomectomy

The GHRH test may represent a new tool in the study of GH dynamics in acromegaly. GH responsiveness to GHRH 1-40 (50 micrograms iv) has been studied in 21 acromegalic patients. Nineteen out of 21 had active disease. Five patients were also studied 1-12 months after neurosurgery. Two apparently cured acromegalics were studied 1-2 yr after surgery. GH secretion has been evaluated in all patients by means of TRH, bromocriptine and insulin hypoglycemia tests, too. GH response to GHRH has also been performed in 14 normal subjects. In acromegaly, GH responses after GHRH (p less than 0.01 vs placebo) were variable. The GH peak ranged from 8 to 445 ng/ml in patients with active disease. Maximum GH increase after GHRH (calculated as peak/basal value ratio) was significantly reduced in acromegaly (2.9 +/- 0.5 ng/ml; mean +/- SE) in comparison to controls (34.1 +/- 10.9 ng/ml; p less than 0.01). No significant differences in GH pattern after GHRH were found between untreated and previously treated patients with active disease. A significant correlation was found between GH basal levels and GH incremental area (p less than 0.05) and between GH basal and peak levels (p less than 0.01) after GHRH. A significant increase in PRL secretion was observed in acromegalic patients after GHRH (p less than 0.01 vs placebo). No discernable variation was found in the other pituitary hormones pattern after the peptide administration. A positive correlation was observed between GH increase after GHRH and insulin hypoglycemia (p less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Treatment of growth-hormone deficiency with growth-hormone-releasing hormone

18 prepubertal growth-hormone (GH)-deficient children were treated with twice-daily subcutaneous injections of a growth-hormone-releasing hormone analogue, GHRH (1-29) NH2. In 12 of the children the height velocity rose on GHRH treatment, and 8 were judged to have shown a worthwhile response to therapy in that their height velocities during the first 6 months of treatment increased by greater than 2 cm/yr (range 2.7-11.2 cm/yr). These 8 children have now been treated for 6 to 18 months and their increase in height velocity has been maintained. In the 14 patients who had previously received human GH (hGH) height velocity on hGH correlated with that on GHRH. 4 of these patients showed growth deceleration with GHRH, for unknown reasons. A pretreatment peak serum GH response of above 30 mU/l during an intravenous GHRH test was predictive of a good growth response to GHRH but a lower peak did not preclude a growth response. There was no consistent evidence of a priming or desensitisation effect of therapy on the GH responses to GHRH. Although anti-GHRH antibodies developed in 14 patients, these did not seem to have adverse effects on either growth or the GH responses to GHRH. GHRH (1-29) NH2 therapy is an alternative to conventional hGH in the treatment of some GH-deficient children. Ideal dose regimens need to be established.

Nine months' subcutaneous therapy with synthetic growth hormone releasing factor in children with short stature

The growth promoting potential of GRF(1-29)NH2 was studied in nine boys with short stature over three periods of 3 months. Their short stature was due to partial hGH deficiency/hGH neurosecretory dysfunction and was diagnosed by arginine and insulin stimulation tests and hGH nocturnal profiles. Four patients (Group I) were given GRF, 3-4 micrograms/kg s.c. b.d. during the first period of 3 months, and after an interval of 1 month, the same dose once daily during the second treatment period of 3 months. Five patients (Group II) were given GRF, 3-4 micrograms/kg s.c., once daily during the first and b.d. during the second 3 months of therapy. After a second interval of 1 month without any GRF treatment, the third 3-month period for both groups consisted of one daily injection of GRF, 8-10 micrograms/kg s.c. at 19.00 hours. Total body height and lower leg length were measured by stadiometry and knemometry, respectively. GRF intravenous bolus tests were performed in each patient following fasting, before and at the end of the first and second 3-month periods. Serum IGF-1 and urinary hydroxyproline excretion were determined monthly. Stadiometric growth rate, determined over the whole study period of 11 months including the treatment-free intervals, increased from 4.92 cm/year to 5.97 cm/year (p greater than 0.05). Mean knemometric growth rates increased from 0.28 mm/week before therapy, to 0.35 mm/week during the one injection/day period at low dose, to 0.39 mm/week (p less than 0.05) during the b.d. period, and to 0.40 mm/week during the last 3 months of high-dose GRF given once daily.(ABSTRACT TRUNCATED AT 250 WORDS)

Plasma growth hormone (GH) responses to growth hormone releasing factor (hp GRF 1-44) in familial GH deficiency

In four children with familial GH deficiency peak and integrated GH responses to an acute intravenous bolus of hp GRF 1-44 were lower than in 18 children with non-familial idiopathic GH deficiency and in 5 children with structural hypothalamic abnormalities. It is possible that the familial forms of GH deficiency described may be due to absence or biological inactivity of endogenous GRF or possibly GRF receptor or post receptor abnormalities.

Lesch-Nyhan syndrome: growth delay, testicular atrophy and a partial failure of the 11 beta-hydroxylation of steroids

There is a failure of growth in hypoxanthine guanine phosphoribosyltransferase deficiency; slow weight gain is marked after the second year of age but is apparent in the birth weights of all eight of our patients for whom we have data. However, head growth and bone development are less affected than weight. A partial defect in the adrenocortical 11 beta-hydroxylation of steroids was demonstrated after ACTH stimulation in all four patients studied. This hydroxylation takes place in mitochondria the function of which is modulated by purine nucleotide concentrations; this may be the link with the enzyme defect. Testicular atrophy at autopsy was found in two pubertal age boys and seven patients aged 12-17 years had no signs of puberty. All five boys aged 3-11 years showed less than the normal mean response of plasma testosterone concentration to human chorionic gonadotrophin despite the normal histological appearance of the testes of one 6-year-old-boy. Follicle stimulating hormone responses to gonadotrophin releasing hormone are probably less than in normal in at least three of the seven prepubertal boys. The absence of the normally high activities of hypoxanthine guanine phosphoribosyltransferase in testes appears to inhibit their ability to respond to gonadotrophin.

Growth hormone pretreatment in man blocks the response to growth hormone-releasing hormone; evidence for a direct effect of growth hormone

The effect of pretreatment with biosynthetic methionyl human GH (hGH) on the GH response to GHRH has been studied in normal subjects. Eight volunteers were given either 4 IU hGH or placebo s.c. 12-hourly for 72 h before a GHRH test, or a single s.c. dose of 4 IU hGH 12 h before a GHRH test. Somatomedin-C (Sm-C) levels at the time of the GHRH tests were significantly elevated after treatment with hGH compared to placebo, and the GH response to GHRH was significantly attenuated. A further six subjects were given 2 IU hGH or placebo i.v., and i.v. GHRH 3 h later; there was no rise in Sm-C for the 5 h of the study after either treatment; nevertheless, the response to GHRH was completely abolished by pretreatment with hGH. These results demonstrate that GH can regulate its own secretion independently of changes in Sm-C levels, through a mechanism other than the inhibition of GHRH release. The attenuated response to GHRH in the presence of elevated Sm-C levels may be related to Sm-C, or be a more direct effect of the recently elevated GH levels.

Testing with growth hormone-releasing factor (GRF(1-29)NH2) and somatomedin C measurements for the evaluation of growth hormone deficiency

Growth hormone (GH) responses to GRF (1 microgram/kg BW i.v.) were investigated. Comparison between GRF(1-40) and GRF(1-29)NH2 in 11 young adult volunteers gave identical results. One hundred and thirty-one children and adolescents (45 with idiopathic GHD) were tested with GRF (1-29)NH2. The maximal GH levels (max GH) in response to GRF during the 120 min test period were found suitable to characterize the response. In cases without GHD no correlation to age, sex and pubertal development was observed. A maximal GH level of above 10 ng/ml was found to be normal. In 3 out of 86 children without GHD (one with Turner syndrome; two with simple obesity) max GH fell short of 10 ng/ml, while 11 of 45 cases with GHD exceeded this margin. In GHD, max GH was inversely correlated with age. There was no difference in max GH between groups with or without perinatal pathology as a presumed cause of GHD. GH levels to GRF were positively correlated with maximal GH level during sleep in GHD, but not correlated with responses seen to insulin or arginine. The value of GRF testing for the confirmation of GHD is discussed in the light of other GH stimulatory tests and basal somatomedin C measurements. It is suggested that the combination of testing with GRF and the determination of a basal SmC level offers a safe and convenient way to diagnose GHD in clinically suspected cases, though in some cases further diagnostic tests may be needed.