Activation of growth hormone releasing hormone (GHRH) receptor stimulates cardiac reverse remodeling after myocardial infarction (MI).

Both cardiac myocytes and cardiac stem cells (CSCs) express the receptor of growth hormone releasing hormone (GHRH), activation of which improves injury responses after myocardial infarction (MI). Here we show that a GHRH-agonist (GHRH-A; JI-38) reverses ventricular remodeling and enhances functional recovery in the setting of chronic MI. This response is mediated entirely by activation of GHRH receptor (GHRHR), as demonstrated by the use of a highly selective GHRH antagonist (MIA-602). One month after MI, animals were randomly assigned to receive: placebo, GHRH-A (JI-38), rat recombinant GH, MIA-602, or a combination of GHRH-A and MIA-602, for a 4-wk period. We assessed cardiac performance and hemodynamics by using echocardiography and micromanometry derived pressure-volume loops. Morphometric measurements were carried out to determine MI size and capillary density, and the expression of GHRHR was assessed by immunofluorescence and quantitative RT-PCR. GHRH-A markedly improved cardiac function as shown by echocardiographic and hemodynamic parameters. MI size was substantially reduced, whereas myocyte and nonmyocyte mitosis was markedly increased by GHRH-A. These effects occurred without increases in circulating levels of growth hormone and insulin-like growth factor I and were, at least partially, nullified by GHRH antagonism, confirming a receptor-mediated mechanism. GHRH-A stimulated CSCs proliferation ex vivo, in a manner offset by MIA-602. Collectively, our findings reveal the importance of the GHRH signaling pathway within the heart. Therapy with GHRH-A although initiated 1 mo after MI substantially improved cardiac performance and reduced infarct size, suggesting a regenerative process. Therefore, activation of GHRHR provides a unique therapeutic approach to reverse remodeling after MI.

Antagonists of growth hormone-releasing hormone (GHRH) reduce prostate size in experimental benign prostatic hyperplasia.

Growth hormone-releasing hormone (GHRH), a hypothalamic polypeptide, acts as a potent autocrine/paracrine growth factor in many cancers. Benign prostatic hyperplasia (BPH) is a pathologic proliferation of prostatic glandular and stromal tissues; a variety of growth factors and inflammatory processes are inculpated in its pathogenesis. Previously we showed that potent synthetic antagonists of GHRH strongly inhibit the growth of diverse experimental human tumors including prostate cancer by suppressing various tumoral growth factors. The influence of GHRH antagonists on animal models of BPH has not been investigated. We evaluated the effects of the GHRH antagonists JMR-132 given at doses of 40 µg/d, MIA-313 at 20 µg/d, and MIA-459 at 20 µg/d in testosterone-induced BPH in Wistar rats. Reduction of prostate weights was observed after 6 wk of treatment with GHRH antagonists: a 17.8% decrease with JMR-132 treatment; a 17.0% decline with MIA-313 treatment; and a 21.4% reduction with MIA-459 treatment (P < 0.05 for all). We quantified transcript levels of genes related to growth factors, inflammatory cytokines, and signal transduction and identified significant changes in the expression of more than 80 genes (P < 0.05). Significant reductions in protein levels of IL-1ß, NF-κß/p65, and cyclooxygenase-2 (COX-2) also were observed after treatment with a GHRH antagonist. We conclude that GHRH antagonists can lower prostate weight in experimental BPH. This reduction is caused by the direct inhibitory effects of GHRH antagonists exerted through prostatic GHRH receptors. This study sheds light on the mechanism of action of GHRH antagonists in BPH and suggests that GHRH antagonists should be considered for further development as therapy for BPH.

Polyethylene glycol-conjugated growth hormone-releasing hormone is long acting and stimulates GH in healthy young and elderly subjects.

OBJECTIVE: The clinical use of growth hormone-releasing hormone (GHRH) is limited by its short half-life. Polyethylene glycol-conjugated GHRH (PEG-GHRH) was developed to provide increased stability compared with the currently available GHRH(1-29). This study aimed to evaluate the safety, tolerability and pharmacodynamics of PEG-GHRH. DESIGN: PEG-GHRH was administered by subcutaneous injection to young healthy men (n = 12) and elderly men and women (aged > 60 years; n = 20). RESULTS: In both groups, administration of PEG-GHRH generated a clear increase in circulating GH compared with placebo. Following single-dose (0.25, 0.5, 2 or 4 mg) administration to young subjects, the effect persisted for 12 h, but a sustained increase was observed on repeated administration to the elderly. Serum insulin-like growth factor-I also increased in response to PEG-GHRH treatment. Injection-site reactions were more frequent with PEG-GHRH compared with placebo, but these were mild and transient; other adverse events were similar to those observed after placebo. Some impairment of glucose tolerance was observed in the elderly following repeated administration of PEG-GHRH. Antibodies to GHRH were not observed. CONCLUSIONS: PEG-GHRH offers the possibility of less frequent dosing compared with GHRH. This possibility deserves further clinical testing.

Interactions of GRF(1-29)NH2 with plasma proteins and their effects on the release of the peptide from a PLAGA matrix.

The administration of the GRF(1-29)NH2 Growth Hormone Releasing Hormone analog is known as relevant of the concept of drug delivery system using a bioresorbable matrix. However, the release of this peptide from poly(dl-lactic acid-co-glycolic acid) matrices is affected by its insolubility at neutral in salted media and in plasma as well. In order to investigate the origin and the nature of the insolubility in these media in more details, the precipitates collected when the peptide was set in contact with saline, isotonic pH=7.4 phosphate buffer and plasma were analyzed by various techniques, namely weighting, gel chromatography, 1D- and 2D-immunoelectrophoresis, and dialysis to discern the soluble from the insoluble or aggregated fractions. It is shown that precipitation in protein-free salted media is due to a salting out phenomenon complemented by the neutralization of the solubilizing electrostatic charges in the isotonic buffer. In contrast, the precipitation in plasma is due to inter polyelectrolyte-type complexation that involved polyanionic proteins having a rather low isoelectric point like albumin, transferin, haptoglobulin and IgG immunoglobulins. When a rather large quantity of GRF(1-29)NH2 was entrapped in bioresorbable pellets working at a percolating regime after subcutaneous implantation in rats, the peptide was slowly released despite the complexation with plasma proteins. However only a very small part of the peptide was found in blood, this small part being still large enough to cause a detectable increase of the circulating growth hormone concentration. Attempts made to increase the solubility of the peptide in plasma were successful when the peptide was combined with arginine, an amino acid known to promote the poor hormonal activity of injected GRF(1-29)NH2 solutions under clinical conditions.

Intracerebroventricular administration of the growth hormone-releasing peptide KP-102 increases food intake in free-feeding rats.

Recent evidence suggests that growth hormone-releasing peptides (GHRPs) mimic an unidentified native GH-releasing hormone (GHRH)-amplifying hormone. GHRH has been shown to stimulate food intake acting on the central nervous system. The present studies were conducted to test the hypothesis that GHRPs may also potentiate the central effect of GHRH on feeding in free-feeding rats. Intracerebroventricular (ICV) administration of picomole doses of a newly developed GHRP, KP-102, or human GHRH stimulated feeding, but the phenomenon was not reproduced by systemic injection. A prior ICV injection of a GHRH antagonist completely prevented the increase of food intake evoked by GHRH, but this pretreatment did not influence the increase in food intake induced by KP-102. When maximally effective doses of GHRH and KP-102 were co-administered ICV, the amount of food intake increased significantly compared with after ICV injection of a maximum dose of either peptide alone. These findings suggest that GHRPs stimulate food intake via a specific receptor for GHRPs in the central nervous system and amplify the central effect of GHRH on feeding.

Endocrine and metabolic effects of long-term administration of [Nle27]growth hormone-releasing hormone-(1-29)-NH2 in age-advanced men and women.

Attenuation of the GH and insulin-like growth factor I (IGF-I) axis in aging may be responsible for changes in body composition and metabolism. This relationship has been confirmed by studies of recombinant human GH replacement in aging men and women, but the adverse effects encountered limit its clinical utility. The use of GHRH or its analogs may be an alternative mode for restoring the GH-IGF-I axis in aging individuals. Here we report the endocrine-metabolic changes in response to a GHRH analog in age-advanced men and women. A single blind, randomized, placebo-controlled trial of 5 months duration was conducted. Ten women and 9 men between the ages of 55-71 yr self-injected placebo (saline) s.c. nightly for 4 weeks followed by 16 weeks of [Nle27]GHRH-(1-29)-NH2 at a dose of 10 microg/kg. Subjects underwent 12-h nocturnal (2000-0800 h) frequent blood sampling (10-min intervals) and 24-h urine collection at baseline, after 4 weeks of placebo injections, and after 16 weeks of GHRH analog administration. GH responses to GHRH analog and spontaneous GH pulsatility were assessed. Subjects were also monitored 2, 4, 8, and 12 weeks after commencement of GHRH analog treatment. Blood pressure, body weight, and fasting insulin and glucose levels were recorded at each visit. Serum concentrations of IGF-I, IGF binding protein-1 (IGFBP-1), IGFBP-3, GH-binding protein (GHBP), lipids, and safety laboratory tests (complete blood count and chemistry profile) were measured in fasting samples (0800-0900 h). Body composition was determined by dual energy x-ray absorptiometry scan, and skin thickness was measured at four sites, including the right and left hand and volar forearm, by Harpenden skin calipers. Insulin sensitivity was assessed by a frequently sampled i.v. glucose tolerance test. Quality of life parameters, including sleep, were evaluated through self-administered questionnaires. Nightly GHRH analog administration at 2100 h induced, within 10 min, an acute release of GH, which lasted for 2 h. The GH-releasing effect of GHRH analog was sustained during the course of the study. Compared with placebo, GHRH analog induced a significant increase in 12-h integrated nocturnal GH levels in women (P < 0.01) and men (P < 0.05). This was accompanied, within 2 weeks, by increased serum levels of IGF-I (P < 0.05) and IGFBP-3 (P < 0.001), but not IGFBP-1, which remained elevated for 12 weeks, returning toward baseline by 16 weeks in both genders. Within 4 weeks, GHBP concentrations were significantly increased (P < 0.01) in women, but not in men. Although blood pressure and body weight were unaffected, GHRH analog treatment resulted in a significant increase in skin thickness (P < 0.05) in both genders and increased lean body mass in men only (P < 0.05), with no other changes in body composition or bone mineral density in either gender. There was a trend for a positive nitrogen balance in both genders, which became significant (P = 0.03) when the data were combined. Fasting insulin and glucose levels were unaltered, but a significant increase in insulin sensitivity occurred in men (P < 0.05), but not in women. Assessment of quality of life parameters revealed a significant improvement in general well-being (P < 0.05) and libido (P < 0.01) in men, but not in women, and sleep quality was unaffected in both genders. The only adverse side-effect was transient hyperlipidemia, which resolved by the end of the study. We conclude that nightly administration of GHRH analog for 4 months in age-advanced men and women activated the somatotropic axis. Although an increase in skin thickness was found in both genders, increases in lean body mass, insulin sensitivity, general well-being, and libido occurred in men but not in women. These observations suggest that GHRH analog administration induced anabolic effects favoring men more than women. Further studies are needed to define the gender differences observed in response to GHRH analog administration.

Low-dose growth hormone-releasing hormone tests: a dose-response study.

We have evaluated parameters of the serum growth hormone (GH) concentration response to saline and 1-, 10- and 100-micrograms intravenous bolus doses of amide analogue of GH-releasing hormone (GHRH (1-29)NH2) given in random order to 10 adult male volunteers of median body weight 68 (60-90)kg. Compared with saline, both 10- and 100-micrograms GHRH(1-29)NH2 doses (but not 1 microgram) resulted in significant peak GH responses (means and 95% confidence intervals: 24.03 (11.22-51.29) vs 26.09 (16.40-41.50) mU/l, respectively). Although the average rate of serum GH rise was similar after both 10 micrograms (2.05 (1.13-2.97) mU.l-1.min-1) and 100 micrograms of GHRH(1-29)NH2 (1.52 (0.69-2.35) mU.l-1.min-1; ANOVA F = 0.93, p = 0.35), the average rate of serum GH decline after peak GH was slower after the higher dose (10 micrograms vs 100 micrograms: 0.65 (0.40-0.90) vs 0.37 (0.23-0.50) mU.l-1.min-1; ANOVA F = 5.14, p = 0.04), suggesting continued GH secretion. Increasing GHRH(1-29)NH2 doses delayed the time to peak GH (1 microgram: 7.00 (3.50-10.52) min; 10 micrograms: 15.80 (13.62-17.98) min; 100 micrograms: 24.80 (18.40-31.12) min) and serum GH levels were still elevated significantly 2 h after injection of 100 micrograms GHRH(1-29)NH2 compared with other doses (saline: 0.98 (0.48-2.04) mU/l; 1 microgram: 0.68 (0.48-0.93) mU/l; 10 micrograms: 1.07 (0.56-2.04) mU/l; 100 micrograms: 5.01 (2.34-10.86) mU/l; ANOVA F = 11.10, p < 0.001). In a second study we tested five adult male volunteers with lower doses (0.5-10 micrograms) of GHRH(1-29)NH2.(ABSTRACT TRUNCATED AT 250 WORDS)

Evaluation of growth hormone (GH) responses to pulsed GH-releasing hormone administration using the MTT-ESTA bioassay.

We compared the immunoactivity of human growth hormone (hGH) with its bioactivity after stimulation of hGH release into the circulation by the administration of growth hormone-releasing hormone [GHRH(1-29)-NH2] according to a pre-determined protocol to four normal adult volunteers. We used the Hybritech immunoradiometric assay to measure the immunoactive GH concentrations. Bioactive GH concentrations were measured using the highly quantitative and precise eluted stain bioassay system (ESTA). The high sample capacity of the ESTA bioassay permitted us to monitor the bioactivities in closely timed sequential samples, and in far greater detail than has previously been possible. Two pulses of GHRH(1-29)-NH2 were administered intravenously to the four adult male volunteers (aged 24-37 years) on a weekly basis over a 4-week period. Two different doses of GHRH(1-29)-NH2 (0.1 and 1.0 micrograms/kg) were tested. These were separated by specified time intervals (60 or 120 min). Responses in the four individuals were variable. However, although the immuno- and bioactivities generally agreed well, there was a systematic and progressive increase in the bioactivity/immunoactivity (B/I) ratios as half of the response peaks were approached. After these peak concentrations, the B/I ratios subsequently returned to values that were close to unity. The enhanced bioactivity of the peak samples from the two volunteers in whom the largest magnitudes of response were observed was found to be labile after long-term storage at -20 degrees C. We suggest that the preferential rise in GH bioactivity, as opposed to immunoactivity, in response to GHRH(1-29)-NH2 was due to progressive changes in the concentrations of isoforms of GH that are not detectable in the Hybritech immunoassay.

Somatotrope responsiveness to Hexarelin, a synthetic hexapeptide, is refractory to the inhibitory effect of glucose in obesity.

Both spontaneous and stimulated growth hormone (GH) secretion is reduced in obesity, in which state insensitivity to the inhibitory effect of hyperglycemia also has been reported. To further investigate this point, in eight male obese (OB) patients (27-49 years old; body mass index = 39.5 +/- 1.7 kg/m2) we studied the effect of oral glucose load (100 g) on the GH response to Hexarelin (HEX, 2 micrograms/kg iv), a synthetic hexapeptide belonging to the GH-releasing peptide family, which has been reported to be able to induce a marked GH rise even in obese patients. As a control group, six male age-matched normal subjects (NS) were studied (26-35 years old; body mass index = 22.3 +/- 1.5 kg/m2). In all subjects the GH response to growth hormone-releasing hormone (GHRH, 1 microgram/kg iv) was also studied. Basal GH and insulin-like growth factor I (IGF-I) levels in OB and NS were similar (0.3 +/- 0.1 vs 0.5 +/- 1.0 microgram/l and 166.7 +/- 12.3 vs 145.4 +/- 6.9 micrograms/l, respectively). Hexarelin induced a clear GH rise in OB (peak: 20.0 +/- 2.9 micrograms/l; AUC: 1193.0 +/- 213.7 micrograms.l-1.120 min-1) but this response was clearly lower (p < 0.0002) than that observed in NS (62.6 +/- 7.3 micrograms/l, 4587.5 +/- 614.9 micrograms.l-1.120 min-1). The GHRH-induced GH rise was lower (p < 0.002) in OB (4.4 +/- 1.2 micrograms/l, 331.0 +/- 95.9 micrograms.l-1.120 min-1) than that in NS (20.2 +/- 1.9 micrograms/l, 1281.0 +/- 157.5 micrograms.l-1 .120 min-1) and both were lower (p < 0.05) than those induced by HEX. In NS, glucose significantly blunted the GH response to HEX (38.4 +/- 7.2 micrograms/l, 2236.5 +/- 514.8 micrograms.l-1.120 min-1, p < 0.05) but failed to modify it in OB (19.4 +/- 2.7 micrograms/l, 934.5 +/- 151.3 micrograms.l-1. 120 min-1). Plasma glucose peaks after oral glucose load in OB and NS were similar (164.5 +/- 9.7 vs 145.8 +/- 4.6 mg/dl). In conclusion, the present data demonstrate that, in contrast to normal subjects, in obese patients HEX has a reduced GH-releasing effect that is not inhibited by glucose. In OB patients as well as in normal subjects HEX releases more GH than GHRH. These findings strengthen the evidence that GH secretion in obesity is refractory either to stimulatory inputs or to the inhibitory effect of hyperglycemia.

Growth hormone (GH)-releasing effects of synthetic peptide GH-releasing peptide-2 and GH-releasing hormone (1-29NH2) in children with GH insufficiency and idiopathic short stature.

To investigate how growth hormone (GH)-releasing peptide (GHRP) and GH-releasing hormone (GHRH) interact in patients with short stature, we examined the acute effects of GHRH1-29NH2, GHRP-2, and the combination of GHRH1-29NH2 and GHRP-2 on GH release in children with GH insufficiency ([GHI] group A) and idiopathic short stature ([ISS] group B). Ten children with GHI (aged 11.8 +/- 1.1 years; height, -4.2 +/- 0.5 SDS) and five children with ISS (aged 11.1 +/- 1.2 years; height, -3.2 +/- 0.1 SDS) were studied. Intravenous bolus infusions of GHRH1-29NH2 (1 micrograms/kg), GHRP-2(1 microgram/kg), and GHRH plus GHRP-2 (each 1 micrograms/kg), were administered in a randomized order. Because of the variability of GH responses, results were analyzed by a nonparametric statistical method. Patients in group A showed low GH responses to both GHRH1-29NH2 and GHRP-2 stimulation: in only three of 10 and one of nine cases, respectively, were the peak GH levels above 5.0 micrograms/L. GH area under the curve (AUC) 90 minutes after GHRP-2 administration was slightly less than for GHRH1-29NH2 (179 +/- 150 v 214 +/- 68 micrograms/L.min, P = .06). In group B, GH responses to GHRH1-29NH2 and GHRP-2 were approximately of the same magnitude (1,943 +/- 819 v 1,981 +/- 887 micrograms/L.min, P = .9).(ABSTRACT TRUNCATED AT 250 WORDS)

Inhibition of GH release of rats by new potent antagonists of growth hormone-releasing hormone (GH-RH).

Biological activity of a new series of potent GH-RH antagonists containing formyl or phenylacetyl group at the N-terminus of the sequence [D-Arg2,Phe(4-Cl)6,Nle27]hGH-RH(1-29)NH2, as well as various substitutions in positions 8, 15, or 28, and in some cases Agm in position 29, was evaluated in vivo. All five antagonists, administered at a 27-fold molar excess to rats, suppressed the GH-releasing effect of exogenous GH-RH(1-29)-NH2 by 64-75%. The inhibitory effects lasted for more than 15 min. The most potent analogue, PhAc-[D-Arg2,Phe(4-Cl)6,Abu15,Nle27]hGH-RH(1-28)Agm (MZ-5-156), showed an in vivo potency 7-16 times higher than the early antagonist [Ac-Tyr1,D-Arg2]hGH-RH(1-29)-NH2, which was used as standard. MZ-5-156 was capable of decreasing serum GH levels after intravenous, intraperitoneal, or intramuscular administration. In vitro, in the superfused rat pituitary cell system, MZ-5-156 induced a prolonged inhibition of GH release after continuous long-term administration and showed a potency more than 100 times greater than the standard antagonist. These results show that N-terminal acylation with phenylacetic acid of the sequence [D-Arg2,Phe(4-Cl)6,Nle27]hGH-RH(1-29)-NH2, containing modifications in positions 8, 15, 28, or 29, results in antagonists with high and protracted potency both in vivo and in vitro. In view of high antagonistic activity and prolonged duration of action, some of these antagonists of GH-RH may find clinical application for the treatment of IGF-dependent cancers.

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.

Growth hormone release by the novel GH releasing peptide hexarelin in patients with homozygous beta-thalassemia.

Patients with beta-thalassemia often present with abnormalities in growth and other endocrine functions. Growth hormone (GH) secretion is controlled via somatostatin and growth hormone releasing hormone (GHRH). Recently, Hexarelin, a new potent GH secretagogue (His-D-2-Methyl-Trp-Ala-Trp-D-Phe-Lys-NH2), was synthesized. Our study was designed to assess and compare its efficacy as a GH secretagogue to GHRH 1-29 in beta-thalassemia. Eighteen patients, regularly transfused and chelated, were studied; 11 were short statured. None had diabetes mellitus, hypothyroidism, hypopara-thyroidism or major organ failure. We measured GH at 0, 30, 60, 90, 120 min after GHRH 1-29 or Hexarelin administration. Hexarelin p.o. or i.v. evoked a brisk rise of serum GH which was significantly higher (p < 0.01) than that induced by GHRH 1-29 i.v. In conclusion, Hexarelin has greater GH releasing capacity than GHRH 1-29 at 1 microgram/kg i.v. and can thus be viewed as a potential therapeutic agent in GH deficient states.

Effect of long-term GHRH and somatostatin administration on GH release and body weight in prepubertal female rats.

In order to find a chronic GHRH administration capable of stimulating growth rate without depleting pituitary GH content, prepubertal female rats were subcutaneously (sc) treated with GHRH (1-29)-NH2 and somatostatin (SS). In experiment 1, the rats received sc injections of GHRH and cyclic natural SS for 19 days. In the second study, female rats were continuously treated during 21 days with GHRH, using a slow release pellet, alone or combined with one daily injection of long acting SS (octreotide). In experiment 1, body weight was significantly increased when GHRH was administered at the highest daily dosage (1200 microg/day), accompanied by an slight increment in pituitary GH content. Hypothalamic SS concentrations decreased when GHRH or SS were administered alone whereas the combined treatment with both peptides did not modify this parameter, which suggests the existence of a balance between the chronic actions of both peptides on hypothalamus. In experiment 2, the continuous infusion of GHRH increased plasma GH levels and tended to enhance pituitary GH content. Nevertheless, GHRH effect was not effective enough to increase body weight. By adding one daily injection of SS both GHRH effects on the pituitary gland were abolished. Our study indicates that female rats retain responsiveness to chronic GHRH and SS treatments at both pituitary and hypothalamic levels.

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 hormone (GH) profiles in response to continuous subcutaneous infusion of GH-releasing hormone(1-29)-NH2 in children with GH deficiency.

Six children presenting with partial growth hormone (GH) deficiency (mean GH peak in two different tests, 8.0 +/- 1.3 micrograms/l) aged 8-10.3 years (mean, 2.7 +/- 0.9 years) were treated for 6 months by continuous subcutaneous infusion of GH-releasing hormone(1-29)-NH2 (GHRH(1-29)-NH2); 24-hour GH profiles and height velocity were measured. A biphasic effect of GHRH(1-29)-NH2 infusion was observed. After an early substantial increase in the 24-hour integrated concentration of GH, from 1.6 +/- 0.1 to 3.5 +/- 0.7 micrograms/l/minute, a subsequent consistent decrease occurred by 3 months, which was more pronounced after 6 months (mean 24-hour integrated concentration of GH, 1.9 +/- 0.9 micrograms/l/minute). This effect reflects modification of both pulse amplitude and frequency of GH secretion. At the end of the study, one child had complete suppression of GH secretion and two others showed only one peak above 5 micrograms/l during a 24-hour period. No correlation was found between these changes and height velocity. Three children did not grow significantly; the other three children who had a growth response to GHRH(1-29)-NH2 were those with the lowest 24-hour integrated GH concentration at the end of the study. The possible mechanisms involved in this biphasic effect, including GHRH antibodies, changes in somatostatin levels and/or desensitization of pituitary GHRH receptors, have been investigated.

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)

A comparative study of growth hormone (GH) and GH-releasing hormone(1-29)-NH2 for stimulation of growth in children with GH deficiency.

In this study, 60 patients with proven growth hormone deficiency (GHD) of hypothalamic origin were randomized into three equal groups, and received growth hormone-releasing hormone(1-29)-NH2 (GHRH(1-29)-NH2), 30 or 60 micrograms/kg/day, or growth hormone (GH), 0.1 IU/kg/day, for 6 months. There were no significant differences in growth between the two groups given GHRH(1-29)-NH2, but growth in the GH group was significantly better than in the other two groups (p < 0.01). Mean height velocities at 6 months were 9.2, 9.3 and 14.6 cm/year for the three groups, respectively. Plasma GHRH concentrations increased steadily over the 6-month treatment period, with higher levels in the group on the higher dose. During GHRH(1-29)-NH2 treatment, serum concentrations of insulin-like growth factor I rose initially, but then fell to values similar to those before treatment. No GH antibodies were detected, but all 20 patients on high-dose GHRH(1-29)-NH2 and 19 of 20 patients on low-dose GHRH(1-29)-NH2 developed GHRH antibodies. These had almost disappeared by 9 months after stopping treatment. There was no correlation between antibody titres and increase in height. No serious side-effects were seen, but three patients receiving GHRH(1-29)-NH2 reported mild irritation at the injection site. These results from the continuous infusion of GHRH(1-29)-NH2 over 6 months suggest that this treatment, or the related use of a depot preparation, is unlikely to be as effective as GH for the promotion of growth in GHD.

Intranasal administration of growth hormone-releasing hormone(1-29)-NH2 in children with growth hormone deficiency: effects on growth hormone secretion and growth.

The growth-promoting potential of growth hormone-releasing hormone(1-29)-NH2 (GHRH(1-29)-NH2) in a new formulation for intranasal use was examined in a 6-month pilot study of eight short prepubertal children. The maximal plasma concentration of growth hormone (GH) was below 12 micrograms/l in two stimulation tests (arginine, insulin), but above 12 (24-90) micrograms/l after intravenous GHRH, 1 microgram/kg. GHRH, 50 micrograms/kg, was insufflated intranasally three times per day over 6 months. On day 1, GHRH insufflations were followed by distinct GHRH and GH plasma peaks, ranging from 1.2 to 5.4 micrograms/l and from 10 to 85 mIU/l, respectively. Peak amplitudes were variably reduced after 6 weeks in most patients, and further reduced at 6 months. GHRH antibodies (initially negative) were positive in three patients after 6 weeks. The mean knemometric growth rate rose from 0.24 to 0.48 mm/week after 6 weeks of treatment (p = 0.03) and then rapidly declined; the mean 6-month stadiometric height velocity did not increase. Local tolerance was good in one patient; most others reported sneezing immediately after insufflation, rhinorrhoea and mild mucosal burning. Treatment was discontinued in two patients after 6 and 12 weeks. It is concluded that intranasal GHRH, though non-invasive, is not suitable in its present form for use in children, because of decreasing absorption and effectiveness with concomitant development of antibodies and local reactions.

The combination of antagonists of LHRH with antagonists of GHRH improves inhibition of androgen sensitive MDA-PCa-2b and LuCaP-35 prostate cancers.

BACKGROUND: Antagonists of growth hormone-releasing hormone (GHRH) could extend the duration of response of androgen sensitive prostate cancers to androgen deprivation. METHODS: We investigated the effect of new GHRH antagonists MZ-J-7-118 and MZ-J-7-138 and luteinizing hormone-releasing hormone (LHRH) antagonist Cetrorelix or castration on androgen sensitive MDA-PCa-2b and LuCaP-35 prostate cancer models xenografted into nude mice. Animals bearing androgen-independent LuCaP-35V prostatic cancer model were also treated with MZ-J-7-118. RESULTS: Receptors for LHRH and GHRH were present in MDA-PCA-2b, LuCaP-35, and LuCaP-35V tumors. GHRH antagonists increased the inhibitory effect of surgical castration and LHRH antagonists on androgen sensitive MDA-PCa-2b and LuCaP-35 tumors. The time to relapse of androgen-dependent LuCaP-35 tumors was extended by GHRH antagonists. Growth of androgen-independent LuCaP-35V xenografts was also significantly inhibited by MZ-J-7-118. In MDA-PCa-2b tumors treatment with MZ-J-7-118 caused a significant decrease of VEGF and Cetrorelix or its combination with MZ-J-7-118 reduced EGF. The B(max) of EGF receptors was significantly reduced by Cetrorelix, MZ-J-7-118 and their combination. CONCLUSIONS: Our findings suggest that the use of a combination of antagonists of GHRH and LHRH could improve the therapy for androgen sensitive prostate cancer. Antagonists of GHRH could be also considered for treatment of androgen-independent prostate cancers.