Effects on growth hormone secretion following intravenous and subcutaneous injections of growth hormone-releasing factor (hGRF-44 NH2): comparison of immunoreactive plasma GRF levels

The early story of growth hormone-releasing factor in rats, swine, and cattle

Following the discovery of the growth hormone-releasing factor from a human pancreatic tumor by the group of Guillemin at the Salk Institute in California, research on this factor has exploded. This review article is focused on the results obtained early after this discovery and summarizes the biological effects of this releasing factor on the rat digestive system development and above all on pig, steer, and gilt growth as well as on milk production in lactating sows and cows.

Treatment with growth hormone-releasing hormone (GHRH) 1-44 in children with idiopathic growth hormone deficiency: a randomized double-blind dose-effect study. The GHRH European Multicenter Study (GEMS) Group

One hundred and eleven pre-pubertal children (70 boys, 41 girls, aged 2.5 to 14.3 years) with growth failure (height 2 SD below the mean for chronological age (CA) and height velocity (HV) below the 10th percentile for bone age) due to idiopathic growth hormone deficiency (peak plasma GH < 20 mUI/1 to two standard provocative tests) were treated with GHRH 1-44 NH2. Patient stratification in two classes was performed according to body weight; in each class, patients were randomly allocated to one of seven GHRH doses, from 30 to 300 micrograms/day. GHRH was injected subcutaneously, every evening, for six months in a double-blind fashion. No relationship was found between the absolute or incremental HV during treatment and the dose (range from 1.3-23.1 micrograms/kg/day) of GHRH. However, HV (cm/year) increased from 3.8 +/- 0.1 (mean +/- SEM) before treatment to 6 +/- 0.2 during six months treatment and 47 patients (42%) increased their HV up to at least the mean normal HV for bone age (catch-up growth). Low titer antibodies to GHRH were found in 19 patients (17.1%) at six months; no adverse effect was observed. Our results suggest that patients showing catch-up growth were older, had a height closer to the mean for chronological age and a slower pre-treatment height velocity. Failure to demonstrate a relationship between GHRH dose and changes in growth velocity might be explained by the combination of a placebo effect, insufficient frequency of GHRH administration and heterogeneity of the population.

Interest of growth hormone-releasing hormone administration for improvement of ovarian responsiveness to gonadotropins in poor responder women

OBJECTIVE

We have investigated the beneficial effect of a somatotroph axis stimulation on ovarian response to gonadotropin.

DESIGN

Growth hormone-releasing hormone (GH-RH) was administered in a prospective study in women undergoing an in vitro fertilization protocol.

PATIENTS

Twelve patients were selected for their poor ovarian response to previous stimulations using gonadotropin-releasing hormone analog (GnRH-a) and human menopausal gonadotropins (hMG).

INTERVENTIONS

Five hundred micrograms of GH-RH1-29 were administered two times daily concomitantly with GnRH-a and hMG from day 2 of the cycle to the time of ovulation.

MAIN OUTCOME MEASURES

Stimulation of somatotroph axis was appreciated by measuring over-night urinary growth hormone (GH) output, plasma GH, and insulin-like growth factor I (IGF-I) and follicular fluid (FF) IGF-I. The effects of GH-RH administration on ovarian function were determined by plasma estradiol levels and follicular data.

RESULTS

Administration of GH-RH was associated with a significant improvement of urinary (P less than 0.025) and plasma (P less than 0.001) GH concentrations and of the hormonal response to hMG (P less than 0.01). Levels of IGF-I followed a biphasic plasma variation, and a slight increase in recruited follicles, retrieved oocytes, and FF IGF-I content was also observed.

CONCLUSIONS

Activation of the somatotroph axis by GH-RH enhances the hormonal ovarian response to hMG and may be an adjunctive therapy to improve follicular maturation.

Subcutaneous growth hormone-releasing hormone augments pulsatile nocturnal GH release in GH-insufficient children, but may also raise basal GH secretion

Growth hormone-releasing hormone (GHRH) when given s.c. to GH-insufficient children either as pulses, or once or twice daily, promotes linear growth. These treatment regimens, however, are not ideal as they require frequent drug administration and a significant proportion of patients do not show improved growth. We have now investigated the GH response to a nocturnal s.c. infusion of GHRH (1-29)NH2, at two dosages, 5 and 10 micrograms/kg/h, in a group of five GH-insufficient children. The s.c. infusion of GHRH between 2100 h and 0600 h augmented nocturnal pulsatile GH release in all five children. There was a dose-dependent response for the GH area under the curve (AUC), and mean total GH concentration. The AUC for GH was significantly greater after the 10 than 5 micrograms/kg/h GHRH which in turn was greater than that after placebo; mean (SD) AUC: 14816 (3978), 8125 (1931), 3032 (1582) mU min/l respectively (P less than 0.01 and P less than 0.05). There was no significant change in the number of GH pulses during the 9-h infusions when the subjects were infused with GHRH 10 or 5 micrograms/kg/h compared to placebo, and they occurred at similar times although the number of pulses tended to be greater after GHRH; the mean (SD) numbers of GH pulses were 5.0 (0.7), 3.8 (0.8), 3.2 (0.8), respectively. There was however a significant rise in the mean baseline GH concentration in all patients during the infusion of GHRH 10 micrograms/kg/h compared to placebo, but not with 5 micrograms/kg/h. Thus, GHRH(1-29)NH2 given s.c. augmented nocturnal pulsatile GH release in GH-insufficient children but it also increased baseline GH secretion. These results suggest that a sustained release preparation of GHRH could be a potential treatment for GH-insufficient children, and that a dose of 5 micrograms/kg/h would promote pulsatile GH release, but that at higher dosage it may also raise basal GH secretion.

Growth hormone and somatomedin-C response to synthetic human pancreatic tumor GH-releasing factor in hypopituitary and constitutionally short children

GH and somatomedin-C response to acute hpGRF-44 iv administration (1 microgram/Kg bw) was studied in 16 patients with hypopituitarism (GHD) and in 7 constitutionally short subjects. GH-deficient patients evidenced a significant GH increase peaking between 15 and 60 min. (4.95 +/- 0.88 ng/ml, mean +/- SE) (p less than 0.01 vs placebo). In non GH-deficient subjects GH increase was more pronounced (peak 18.00 +/- 3.01 ng/ml; p less than 0.01 vs both placebo and GHD group). Acid-extractable somatomedin-C was slightly, but significantly higher than baseline at 12th h (p less than 0.01) in both patients with hypopituitarism (basal value: 0.067 +/- 0.021 U/ml; 12 h: 0.096 +/- 0.024 U/ml) and constitutionally short subjects (basal value 0.62 +/- 0.13; 12h 0.72 +/- 0.16 U/ml). In 3 subjects with hypopituitarism multiple iv administrations (1 microgram/kg bw at 09:30 and 21:30 h for 4 days) produced on the average a modest increase of the GH responsiveness, were more effective to enhance somatomedin-C concentration, but not sufficient to reach normal levels. Sc administration of the same dose at 4-h intervals by a programmable portable pump - performed on 6 GHD subjects - produced an increase of GH peak response on the 4th day of treatment (1.38 +/- 0.31 ng/ml) with respect to the one observed on the first day (0.42 +/- 0.09 ng/ml). Somatomedin-C increase was low and inconstant. These data support the use of a 4-5-day pulsatile treatment in the differentiation between hypothalamic and pituitary deficiency, and the possibility of therapeutical use of GRF with the same protocol when a response is evidenced.

Synthetic growth hormone-releasing hormone (GHRH 1-44) in the differential diagnosis between hypothalamic and pituitary GH deficiency

GH response to an iv bolus of growth-hormone-releasing hormone (GHRH 1-44, 2 micrograms/kg iv) was evaluated in 17 prepubertal children with total GH deficiency (GHD), 6 with partial GHD and in 7 prepubertal normal but short children tested as control. GH response to conventional pharmacological (insulin and arginine or L-Dopa) and physiological stimuli (sleep test) and to GHRH test was also compared. GHRH-induced GH peak occurred at variable times and marked heterogeneity in magnitude of the individual responses to this peptide was observed in GHD patients and in controls. GH increases after GHRH with a peak greater than 10 ng/ml suggested an hypothalamic origin of the GHD in 12 patients (8 with total GHD and 4 with partial GHD). A significant difference (p less than 0.025) of GH peak mean following GHRH administration between total GHD children and normal short children was found. GH response to GHRH injection was usually higher than to conventional stimuli. Nevertheless GH peak following GHRH administration was lower than GH peak following conventional stimuli in 6 children (2 partial GHD children and 4 normal ones). A normal short child failed to respond to GHRH test performed twice. GHRH test is an important diagnostic tool in order to point out hypothalamic GHD.

Rapid enzymatic degradation of growth hormone-releasing hormone by plasma in vitro and in vivo to a biologically inactive product cleaved at the NH2 terminus

The effect of plasma on degradation of human growth hormone-releasing hormone (GRH) was examined in vitro and in vivo using high performance liquid chromatography (HPLC), radioimmunoassay (RIA), and bioassay. When GRH(1-44)-NH2 was incubated with human plasma, the t1/2 of total GRH immunoreactivity was 63 min (RIA). However, HPLC revealed a more rapid disappearance (t1/2, 17 min) of GRH(1-44)-NH2 that was associated with the appearance of a less hydrophobic but relatively stable peptide that was fully immunoreactive. Sequence analysis indicated its structure to be GRH(3-44)-NH2. Identity was also confirmed by co-elution of purified and synthetic peptides on HPLC. Biologic activity of GRH(3-44)-NH2 was less than 10(-3) that of GRH(1-44)-NH2. After intravenous injection of GRH(1-44)-NH2 in normal subjects, a plasma immunoreactive peak with HPLC retention comparable to GRH(3-44)-NH2 was detected within 1 min and the t1/2 of GRH(1-44)-NH2 (HPLC) was 6.8 min. The results provide evidence for GRH inactivation by a plasma dipeptidylaminopeptidase that could limit its effect on the pituitary.

Growth hormone releasing hormone

Human growth hormone releasing hormone (GHRH) was originally extracted from two pancreatic tumours in patients with acromegaly, and is now known to consist of a 44 residue amidated peptide or its C-terminal-shortened derivatives. The sequence of rat GHRH has also been determined; this 43 residue peptide shows approximately 70% homology with human GHRH, and is located mainly in the arcuate nucleus of the hypothalamus. Pulsatile GH release in the rat is principally a consequence of the pulsatile release of hypothalamic GHRH, although this appears to be associated with a transient suppression of somatostatin release. Exogenous GHRH specifically increases circulating GH in many species, and in the long term may increase growth. In normal man, several analogues of GHRH have been shown to be safe, sensitive and specific stimuli to GH release; although there may be a variable prolactin response, this is usually of small magnitude. Continuous infusion of GHRH leads to a decrement in responsiveness, due at least in part to changes in hypothalamic somatostatin. The GH response to GHRH is also modulated by obesity, blood sugar, free fatty acids, and GH itself. Many children with 'GH deficiency' (idiopathic, radiation-induced, or secondary to hypothalamopituitary tumours) respond to intravenous GHRH with an acute rise in serum GH. Early studies also indicate that long-term therapy with subcutaneous GHRH may increase growth velocity in some of these children. It is concluded that analogues of GHRH are useful in the investigation of the hypothalamopituitary axis, and may be important in the therapy of short stature.

Clinical studies with human growth hormone releasing factor in normal adults and patients

The recent availability of human growth hormone releasing factor (hGRF) encouraged thorough investigations of human growth hormone secretion. Moreover it is now possible to put forward a therapeutic application for this hormone. Herein, we report the dose-effect relationship obtained between hGRF and GH response in normal young men submitted to IV administration of doses ranging from 2.5 to 600 micrograms per subject, in three protocols. In some subjects the 2.5 micrograms dose elicited GH secretion as compared with placebo. A highly significant dose-effect was observed (based on GH-AUC and GH-peak) for doses ranging from 5 to 80 micrograms. Responses were identical above 80 micrograms. We conclude that the optimal dose required to elicit maximum GH release with minimal unwanted effects is 80 micrograms in adults. These are related to the dose and observed for doses up to 80-150 micrograms. Subcutaneous administration also induced GH-release, with relationship to the doses used (100, 300 and 600 micrograms per subject). The mean response to the highest dose (600 micrograms) was comparable in timing and magnitude to that obtained with a 100 microgram intravenous dose. Bioactivity of GH released under hGRF was proven in the Nb2 lymphoma cell multiplication assay and a high correlation was obtained between bioassay and radioimmunoassay. GH was present in blood after hGRF under 3 molecular forms corresponding to little, big and big-big GH with percentages of 50, 30 and 20, respectively. An early and slight increase in prolactin was found to be related to the hGRF doses above 80 micrograms. No change was observed for doses less than 80 micrograms.(ABSTRACT TRUNCATED AT 250 WORDS)