Growth-hormone-releasing factor in growth hormone deficiency: demonstration of a hypothalamic defect in growth hormone release

Growth hormone releasing factor: comparison of two analogues and demonstration of hypothalamic defect in growth hormone release after radiotherapy

Human pancreatic growth hormone releasing factor (hpGHRF(1-40] stimulates the release of growth hormone in normal subjects and some patients with growth hormone deficiency. A study comparing the shorter chain amidated analogue hpGHRF(1-29) with an equivalent dose of hpGHRF(1-40) in seven normal subjects showed no significant difference in growth hormone response between the two preparations. Six patients with prolactinomas were also tested; these patients had received megavoltage radiotherapy previously but had developed growth hormone deficiency as shown by insulin induced hypoglycaemia. In all six patients 200 micrograms hpGHRF(1-40) or hpGHRF(1-29)NH2 produced an increase in the serum growth hormone concentration. These data suggest that hpGHRF(1-29)NH2 may be useful for testing the readily releasable pool of growth hormone in the pituitary and that cases of hypothalamo-pituitary irradiation resulting in growth hormone deficiency may be due to failure of synthesis or delivery of endogenous GHRF from the hypothalamus to pituitary cells.

Growth-hormone releasing factor and clonidine in children with constitutional growth delay. Evidence for defective pituitary growth hormone reserve

Six male prepubertal children with constitutional growth delay (CGD), and a subnormal growth hormone (GH) response to insulin hypoglycemia, and four normal prepubertal children were given in different occasions 1 microgram/Kg iv synthetic hpGRF-40 or a single oral dose of 0.15 mg/m2 clonidine (Clon), an effective growth hormone (GH) secretagogue. In the normal children brisk and clear-cut GH rises were detected in plasma after hpGRF-40 (peak GH levels at 15-30 min) or clonidine (peak GH levels 60-90 min). In CGD children hpGRF-40 induced a biphasic response, e.g. a slight increase in plasma GH at 15 min followed by a delayed and erratic GH rise occurring 45-120 min post-injection. Also the GH response to Clon was sluggish and delayed and peak plasma GH levels were attained only 90-180 min post-drug administration. These data indicate that the CGD children of our study have a defect in the pituitary GH reserve.

Super-active analogs of growth hormone-releasing factor (1-29)-amide

Human pancreatic growth hormone releasing factor (1-29)-amide [hpGRF (1-29)-NH2] and the following analogs: [D-Tyr-1]-hpGRF(1-29)-NH2, [D-Ala-2]-hpGRF(1-29)-NH2, [D-Asp-3]-hpGRF(1-29)-NH2, and [N-Ac-Tyr-1]-hpGRF (1-29)-NH2 were synthesized using solid phase methodology and tested for their ability to stimulate growth hormone (GH) secretion in the rat and the pig in vivo. [D-Ala-2]-hpGRF (1-29)-NH2 was approximately 50 times more potent than the parent molecule in eliciting GH secretion in the rat. The other analogs were less active, but all were more potent than the 1-29 amide in the rat. [D-Tyr-1]-hpGRF(1-29)-NH2 was 10 times more potent, [D-Asp-3]-hpGRF(1-29)-NH2 7 times more potent, and the acetylated molecule approximately 12 times more potent than hpGRF(1-29)-NH2.

Synthetic hpGRF 1-40 stimulates growth hormone and inhibits prolactin secretion in normal children and children with isolated growth hormone deficiency

Intravenously administered synthetic hpGRF 1-40 at doses of 0.1, 0.33 and 1.0 microgram/kg increased plasma GH in a dose-dependent fashion in 4 normal prepubertal children. hpGRF 1-40 at the dose of 1.0 microgram/kg stimulated GH release, though to a lesser extent than in normals, in 7 children with isolated GH-deficiency (IGHD) but failed to do so in a patient with craniopharyngioma. In all normal children and 6/7 patients with IGHD, hpGRF 1-40 at all doses used induced a clear and sustained lowering of plasma prolactin levels; this effect was lacking in the patient with craniopharyngioma. hpGRF 1-40 had no effect on plasma FSH, LH, TSH or glucose levels nor did it influence pulse rate, blood pressure, or body temperature. These results indicate that hpGRF 1-40 is a potent stimulus to GH release in normal prepubertal children and holds promise for treatment of GH-deficient children. In addition, in both normal children and children with IGHD, hpGRF 1-40 is a potent suppressor of prolactin levels.

Growth hormone neuroregulation and the clinical relevance of somatostatin

The hypothalamus controls GH secretion from the anterior pituitary using two peptides; somatostatin inhibits GH, but physiologically the most important appears to GHRF, the structure of which has recently been discovered by two groups. This exciting development has not only given us further insight into the control of GH secretion, but also posed interesting questions as to the cause of the abnormal GH responses to various stimuli seen in patients with acromegaly. The other hypothalamic peptide controlling GH secretion, somatostatin has been the subject of intensive research in the last ten years. It is widely distributed and has important physiological actions including those involved in GH secretion and its action as a hypothalamic hormone. The secretion and synthesis of these two hypothalamic hormones is in turn modulated by a number of neurotransmitters, the most important of which appears to be dopamine. Knowledge gained in these studies has enabled the development of useful tools in the diagnosis of growth hormone deficiency as well as the only effective medical treatment for acromegaly. Much remains to be learnt of the physiology of growth hormone releasing factor and as a result further patients will benefit in the future.